U.S. patent application number 09/930167 was filed with the patent office on 2002-02-14 for small-sized variable magnification optical system.
Invention is credited to Araki, Keisuke, Nanba, Norihiro.
Application Number | 20020018289 09/930167 |
Document ID | / |
Family ID | 26437145 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018289 |
Kind Code |
A1 |
Nanba, Norihiro ; et
al. |
February 14, 2002 |
Small-sized variable magnification optical system
Abstract
A variable magnification optical system comprises at least three
optical units which are a first moving optical unit, a fixed
optical unit and a second moving optical unit. The three optical
units are arranged in that order in a propagation direction of
light, and a variation of magnification is effected by a relative
movement between the first moving optical unit and the second
moving optical unit. If a ray which exits from an object and enters
the variable magnification optical system, and passes through a
center of a stop of the variable magnification optical system and
reaches a center of a final image plane is represented as a
reference axis ray; a reference axis ray which is incident on any
surface of the variable magnification optical system or enters any
of the optical units is represented as an entering reference axis
of the aforesaid any surface or optical unit; a reference axis ray
which exits from the aforesaid any surface or optical unit is
represented as an exiting reference axis of the aforesaid any
surface or optical unit; a point at which the entering reference
axis intersects with the aforesaid any surface is represented as a
reference point; a direction in which the reference axis ray
travels from an object side toward an image plane along the
entering reference axis is represented as a direction of the
entering reference axis; and a direction in which the reference
axis ray travels from the object side toward the image plane along
the exiting reference axis is represented as a direction of the
exiting reference axis, the second moving optical unit has a cross-
sectional shape which is asymmetrical in a plane which contains the
reference axis, and a curved reflecting surface which is inclined
with respect to the reference axis, and the direction of the
entering reference axis and the direction of the exiting reference
axis of the second moving optical unit are parallel to each other
and differ from each other by 180.degree., the variable
magnification optical system being arranged in such a manner that a
final image is formed after an intermediate image is formed at
least twice.
Inventors: |
Nanba, Norihiro;
(Kawasaki-shi, JP) ; Araki, Keisuke;
(Yokohama-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
26437145 |
Appl. No.: |
09/930167 |
Filed: |
August 16, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09930167 |
Aug 16, 2001 |
|
|
|
09343089 |
Jun 30, 1999 |
|
|
|
6313942 |
|
|
|
|
09343089 |
Jun 30, 1999 |
|
|
|
08828835 |
Mar 24, 1997 |
|
|
|
5999311 |
|
|
|
|
Current U.S.
Class: |
359/365 ;
359/432; 359/676; 359/831 |
Current CPC
Class: |
G02B 15/143107 20190801;
G02B 15/1421 20190801 |
Class at
Publication: |
359/365 ;
359/432; 359/676; 359/831 |
International
Class: |
G02B 017/00; G02B
021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 1996 |
JP |
HEI 08-095988 |
Mar 26, 1996 |
JP |
HEI 08-095991 |
Claims
1. A variable magnification optical system comprising at least
three optical units, said at least three optical units being a
first moving optical unit, a fixed optical unit and a second moving
optical unit which are arranged in that order in a propagation
direction of light, a variation of magnification being effected by
a relative movement between said first moving optical unit and said
second moving optical unit, wherein if a ray which exits from an
object and enters said variable magnification optical system, and
passes through a center of a stop of said variable magnification
optical system and reaches a center of a final image plane is
represented as a reference axis ray; a reference axis ray which is
incident on any surface of said variable magnification optical
system or enters any of said optical units is represented as an
entering reference axis of said any surface or said any optical
unit; a reference axis ray which exits from said any surface or
said any optical unit is represented as an exiting reference axis
of said any surface or said any optical unit; a point at which the
entering reference axis intersects with said any surface is
represented as a reference point; a direction in which the
reference axis ray travels from an object side toward an image
plane along the entering reference axis is represented as a
direction of the entering reference axis; and a direction in which
the reference axis ray travels from the object side toward the
image plane along the exiting reference axis is represented as a
direction of the exiting reference axis, said second moving optical
unit has a cross-sectional shape which is asymmetrical in a plane
which contains the reference axis, and a curved reflecting surface
which is inclined with respect to the reference axis, and the
direction of the entering reference axis and the direction of the
exiting reference axis of said second moving optical unit are
parallel to each other and differ from each other by 180.degree.,
said variable magnification optical system being arranged in such a
manner that a final image is formed after an intermediate image is
formed at least twice.
2. A variable magnification optical system according to claim 1,
wherein said fixed optical unit is an optical unit having the
largest ratio of (a lateral magnification at a wide-angle end) to
(a lateral magnification at a telephoto end) of all the optical
units.
3. A variable magnification optical system according to claim 1,
wherein said first moving optical unit moves toward said fixed
optical unit during a variation of magnification from a wide-angle
end toward a telephoto end.
4. A variable magnification optical system according to claim 1,
wherein said second moving optical unit includes an optical element
which is formed as one transparent body on which two refracting
surfaces and a plurality of internal curved reflecting surfaces are
formed.
5. A variable magnification optical system according to claim 1,
wherein said first moving optical unit includes an optical element
which is formed as one transparent body on which two refracting
surfaces and a plurality of internal curved reflecting surfaces
inclined with respect to the reference axis are formed, the
direction of the entering reference axis and the direction of the
exiting reference axis of said optical element being parallel to
and the same as each other.
6. A variable magnification optical system according to claim 1,
wherein said first moving optical unit includes an optical element
which is formed as one transparent body on which two refracting
surfaces and a plurality of internal curved reflecting surfaces
inclined with respect to the reference axis are formed, the
direction of the entering reference axis and the direction of the
exiting reference axis of said optical element being parallel to
each other and different from each other by 180.degree..
7. A variable magnification optical system according to claim 5,
wherein said first moving optical unit forms an intermediate image
in its inside.
8. A variable magnification optical system according to claim 1,
wherein said fixed optical unit includes an optical element which
is formed as one transparent body on which two refracting surfaces
and a plurality of internal curved reflecting surfaces inclined
with respect to the reference axis are formed, the direction of the
entering reference axis and the direction of the exiting reference
axis of said optical element being parallel to and the same as each
other.
9. A variable magnification optical system according to claim 1,
wherein said fixed optical unit includes an optical element which
is formed as one transparent body on which two refracting surfaces
and a plurality of internal curved reflecting surfaces inclined
with respect to the reference axis are formed, the direction of the
entering reference axis and the direction of the exiting reference
axis of said optical element being parallel to each other and
different from each other by 180.degree..
10. A variable magnification optical system according to claim 1,
wherein said fixed optical unit includes an optical element which
is formed as one transparent body on which two refracting surfaces
and a plurality of internal curved reflecting surfaces inclined
with respect to the reference axis are formed, the exiting
reference axis of said optical element being inclined with respect
to the entering reference axis thereof.
11. A variable magnification optical system according to claim 1,
wherein said stop is located on the object side of said first
moving optical unit, said stop being fixed during the variation of
magnification.
12. A variable magnification optical system comprising at least
three optical units, said at least three optical units being a
first moving optical unit, a fixed optical unit and a second moving
optical unit which are arranged in that order in a propagation
direction of light, a variation of magnification being effected by
a relative movement between said first moving optical unit and said
second moving optical unit, wherein if a ray which exits from an
object and enters said variable magnification optical system, and
passes through a center of a stop of said variable magnification
optical system and reaches a center of a final image plane is
represented as a reference axis ray; a reference axis ray which is
incident on any surface of said variable magnification optical
system or enters any of said optical units is represented as an
entering reference axis of said any surface or said any optical
unit; a reference axis ray which exits from said any surface or
said any optical unit is represented as an exiting reference axis
of said any surface or said any optical unit; a point at which the
entering reference axis intersects with said any surface is
represented as a reference point; a direction in which the
reference axis ray travels from an object side toward an image
plane along the entering reference axis is represented as a
direction of the entering reference axis; and a direction in which
the reference axis ray travels from the object side toward the
image plane along the exiting reference axis is represented as a
direction of the exiting reference axis, each of said first moving
optical unit, said fixed optical unit and said second moving
optical unit includes an optical element which is formed as one
transparent body on which two refracting surfaces and at least one
internal curved reflecting surface inclined with respect to the
reference axis, said second moving optical unit having a
cross-sectional shape which is asymmetrical in a plane which
contains the reference axis, and a curved reflecting surface which
is inclined with respect to the reference axis, and the direction
of the entering reference axis and the direction of the exiting
reference axis of said second moving optical unit are parallel to
each other and differ from each other by .sub.180.degree., said
variable magnification optical system being arranged in such a
manner that a final image is formed after an intermediate image is
formed at least twice.
13. A variable magnification optical system according to claim 12,
wherein, during a variation of magnification from a wide-angle end
toward a telephoto end, an optical path length between said first
moving optical unit and said fixed optical unit becomes shorter,
whereas an optical path length between said fixed optical unit and
said second moving optical unit becomes longer.
14. A variable magnification optical system according to claim 12,
wherein, during the variation of magnification, an optical path
length which extends from the object to the final image forming
plane is varied with the final image forming plane spatially
fixed.
15. A variable magnification optical system according to claim 12,
wherein said stop is located on the object side of said first
moving optical unit, said stop being fixed during the variation of
magnification.
16. An image pickup apparatus comprising said variable
magnification optical system according to claim 1, said image
pickup apparatus being arranged to form an image of an object to be
photographed, on an image pickup surface of an image pickup
medium.
17. A variable magnification optical system comprising a fixed
optical unit and a plurality of magnification varying optical units
which are arranged in that order in a propagation direction of
light, a variation of magnification being effected by a relative
movement between said plurality of magnification varying optical
units, wherein letting f.sub.i be a focal length of any
magnification varying optical unit i and letting k be a number of
times by which an on-axial light beam forms an intermediate image
in said any magnification varying optical unit i, said any
magnification varying optical unit i
satisfies:f.sub.i.multidot.(-1).- sup.k>0 (k is an integer not
less than 0), and wherein if a ray which exits from an object and
enters said variable magnification optical system, and passes
through a center of a stop of said variable magnification optical
system and reaches a center of a final image plane is represented
as a reference axis ray; a reference axis ray which is incident on
any surface of said variable magnification optical system or enters
any of said optical units is represented as an entering reference
axis of said any surface or said any optical unit; a reference axis
ray which exits from said any surface or said any optical unit is
represented as an exiting reference axis of said any surface or
said any optical unit; a point at which the entering reference axis
intersects with said any surface is represented as a reference
point; a direction in which the reference axis ray travels from an
object side toward an image plane along the entering reference axis
is represented as a direction of the entering reference axis; and a
direction in which the reference axis ray travels from the object
side toward the image plane along the exiting reference axis is
represented as a direction of the exiting reference axis, any of
said magnification varying optical units includes at least one
concave reflecting surface the entering and exiting reference axes
of which are inclined with respect to a normal to said concave
reflecting surface at the reference point thereof, said concave
reflecting surface having a cross-sectional shape which is
asymmetrical in a plane which contains the entering reference axis
and the exiting reference axis.
18. A variable magnification optical system according to claim 17,
wherein the entering reference axis of a surface which is closest
to an object side in said any magnification varying optical units
and the exiting reference axis of a surface which is closest to an
image side in said any magnification varying optical units are
parallel to each other, said magnification varying optical units
effecting a variation of magnification by moving in parallel with
the entering reference axis.
19. A variable magnification optical system according to claim 18,
wherein said concave reflecting surface has a shape which is
symmetrical with respect to the plane (Y, Z plane) which contains
the entering reference axis and the exiting reference axis.
20. A variable magnification optical system according to claim 19,
wherein an optical path length, which extends from a first surface
numbered from the object side of said fixed optical unit to the
final image forming plane of said variable magnification optical
system, varies during the variation of magnification.
21. A variable magnification optical system according to claim 20,
wherein the direction of the entering reference axis of said
surface which is closest to the object side in said any
magnification varying optical unit and the direction of the exiting
reference axis of said surface which is closest to the image side
in said any magnification varying optical unit differ from each
other by 180.degree..
22. A variable magnification optical system according to claim 21,
wherein focusing is effected by a movement of at least one of said
plurality of magnification varying optical units.
23. A variable magnification optical system according to claim 21,
wherein said magnification varying optical units are two in number
and each of said magnification varying optical units includes at
least three concave reflecting surfaces each of which is identical
to said concave reflecting surface.
24. A variable magnification optical system according to claim 23,
wherein any of said magnification varying optical units has a
negative focal length and forms an on-axial light beam as an
intermediate image once.
25. A variable magnification optical system according to claim 24,
wherein any of said magnification varying optical units includes
five reflecting surfaces which continuously reflect a ray, said
first, third and fifth surfaces numbered from the object side being
concave reflecting surfaces each of which is identical to said
concave reflecting surface.
26. A variable magnification optical system according to claim 25,
wherein, letting D(i-1) be a distance along the reference axis from
an (i-1)st reflecting surface to an i-th reflecting surface on the
reference axis and letting Di be a distance along the reference
axis from the i-th reflecting surface to an (i+1)st reflecting
surface, a distance between each of said reference surfaces of any
of said magnification varying optical units satisfies the following
condition: 15 0.8 < ( Di D ( i - 1 ) ) < 1.2 .
27. A variable magnification optical system according to claim 25,
wherein said reflecting surfaces of each of said magnification
varying optical units are surface mirrors, respectively.
28. A variable magnification optical system according to claim 25,
wherein each of said magnification varying optical units includes
an optical element which is formed as a transparent body on which a
plurality of internal reflecting surfaces as well as an entrance
refracting surface and an exit refracting surface for a light beam
are formed.
29. A variable magnification optical system according to claim 23,
wherein, letting d1 be an amount of movement, during the variation
of magnification, of a magnification varying optical unit which is
closer to the object side between said two optical units, letting
d2 be an amount of movement of a magnification varying optical unit
which is closer to the image side between said two optical units,
and letting L.sub.W be a value of the optical path length from the
first surface to the final image forming plane of said variable
magnification optical system for a wide-angle end, and letting
L.sub.T be a value of the optical path length for a telephoto end,
the following condition is satisfied:L.sub.T=L.sub.W-
+2(d2-d1).
30. A variable magnification optical system according to claim 23,
wherein, regarding any of said concave reflecting surfaces of each
of said magnification varying optical units, letting R.sub.y be a
radius of curvature of a paraxial region of said any concave
reflecting surface in a plane (a Y, Z plane) which contains the
entering and exiting reference axes at the reference point of said
any concave reflecting surface, letting R.sub.x be a radius of
curvature of a paraxial region of said any concave reflecting
surface in a plane (an X, Z plane) which contains the reference
point and a center of curvature of the radius of curvature R.sub.y
and is perpendicular to the Y, Z plane, and letting 2.theta. be an
angle made by the entering reference axis and the exiting reference
axis, the following condition is satisfied: 16 0.4 < ( R x R y 1
cos 2 ) < 2.5 .
31. A variable magnification optical system according to claim 20,
wherein, in a partial system which is formed by an i-th concave
reflecting surface, an (i+1)st reflecting surface, and an (i+2)nd
concave reflecting surface which are numbered from the object side
among concave reflecting surfaces which continuously reflect a ray
in each of said magnification varying optical units, letting
R.sub.y, i and R.sub.y, i+2 be radii of curvature of paraxial
regions in a plane (a Y, Z plane) which contains the entering and
exiting reference axes at the respective reference points of the
i-th concave reflecting surface and the (i+2)nd concave reflecting
surface, the following condition is satisfied: 17 0.5 < ( R y ,
i + 2 R y , i ) < 2.0 .
32. A variable magnification optical system according to claim 23,
wherein letting .beta..sub.W be a lateral magnification for a
wide-angle end from a surface which is closest to the object side
in a magnification varying optical unit which is closer to the
object side between said two magnification varying optical units,
to a surface which is closest to the image side in a magnification
varying optical unit which is closer to the image side between said
two magnification varying optical units, the following conditions
is satisfied:0.5<.vertline..beta..sub.W.vertline.- <1.5.
33. A variable magnification optical system according to claim 23,
wherein a lens which does not move during the variation of
magnification and has a negative refractive power is arranged
between said two magnification varying optical units.
34. A variable magnification optical system according to claim 20,
wherein said fixed optical unit includes an optical element which
is formed as a transparent body on which a plurality of internal
reflecting surfaces as well as an entrance refracting surface and
an exit refracting surface for a light beam are formed.
35. A variable magnification optical system according to claim 34,
wherein the direction of the entering reference axis of a surface
which is closest to the object side in said optical element of said
fixed optical unit and the direction of the exiting reference axis
of a surface which is closest to the image-plane side in said
optical element make an angle of 90.degree..
36. A variable magnification optical system according to claim 34,
wherein the direction of the entering reference axis of a surface
which is closest to the object side in said optical element of said
fixed optical unit and the direction of the exiting reference axis
of a surface which is closest to the image-plane side in said
optical element are the same as each other.
37. A variable magnification optical system according to claim 34,
wherein said stop is located on the object side of said optical
element of said fixed optical unit.
38. A variable magnification optical system according to claim 37,
wherein a lens having a negative refractive power is arranged on
the object side of said stop.
39. A variable magnification optical system according to claim 34,
wherein a lens having a refractive index different from the
refractive index of said optical element is secured to either of
the entrance refracting surface and the exit refracting surface of
said optical element of said fixed optical unit.
40. A variable magnification optical system according to claim 20,
wherein said fixed optical unit includes a plurality of reflecting
surfaces each of which the entering and exiting reference axes are
inclined with respect to a normal to a corresponding one of said
reflecting surfaces at the reference point thereof, each of said
reflecting surfaces being a surface mirror.
41. A variable magnification optical system according to claim 40,
wherein said stop is located on the object side of said plurality
of reflecting surfaces of said fixed optical unit.
42. A variable magnification optical system according to claim 40,
wherein said a prism is arranged on the object side of said
plurality of reflecting surfaces of said fixed optical unit which
has an entrance surface and an exit surface in such a manner that
the direction of the entering reference axis of the entrance
surface and the direction of the exiting reference axis of the exit
surface differ from each other by 90.degree..
43. A variable magnification optical system according to claim 40,
wherein a lens having a positive refractive power is arranged on
the image-plane side of said plurality of reflecting surfaces of
said fixed optical unit.
44. An image pickup apparatus comprising said variable
magnification optical system according to claim 17, said image
pickup apparatus being arranged to form an image of an object to be
photographed, on an image pickup surface of an image pickup medium.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a variable magnification
optical system and an image pickup apparatus using the same and,
more specifically, to an optical arrangement suitable for use in a
video camera, a still video camera, a copying machine and the like
which are arranged to realize variation of magnification by using
an optical unit having decentered reflecting surfaces, as a
magnification varying optical unit.
[0003] 2. Description of Related Art
[0004] It is known that an optical system of the type which is
composed of only refracting lenses has been provided as a variable
magnification optical system. In such a conventional optical
system, refracting lenses each having a spheric surface or aspheric
surface of rotational symmetry are rotationally symmetrically
arranged with respect to the optical axis.
[0005] In addition, various photographing optical systems using
reflecting surfaces such as concave mirrors or convex mirrors have
heretofore been proposed, and an optical system using both a
reflecting system and a refracting system is also well known as a
catadioptric system.
[0006] FIG. 37 is a schematic view of a so-called mirror optical
system which is composed of one concave mirror and one convex
mirror. In the mirror optical system shown in FIG. 37, an object
light beam 104 from an object is reflected by a concave mirror 101
and travels toward an object side while being converged, and after
having been reflected by a convex mirror 102 and having been
refracted by a lens 110, the object light beam 104 forms an image
of the object on an image plane 103.
[0007] This mirror optical system is based on the construction of a
so-called Cassegrainian reflecting telescope, and is intended to
reduce the entire length of the optical system by bending, by using
the two opposed reflecting mirrors, the optical path of a telephoto
lens system which is composed of refracting lenses and has an
entire large length.
[0008] For similar reasons, in the field of an objective lens
system which constitutes part of a telescope as well, in addition
to the Cassegrainian type, various other types which are arranged
to reduce the entire length of an optical system by using a
plurality of reflecting mirrors have been known.
[0009] As is apparent from the above description, it has heretofore
been proposed to provide a compact mirror optical system by
efficiently bending an optical path by using reflecting mirrors in
place of lenses which are commonly used in a photographing lens
whose entire length is large.
[0010] However, in general, the mirror optical system, such as the
Cassegrainian reflecting telescope, has the problem that part of an
object ray is blocked by the convex mirror 102. This problem is due
to the fact that the convex mirror 102 is placed in the area
through which the object light beam 104 passes.
[0011] To solve the problem, it has been proposed to provide a
mirror optical system which employs decentered reflecting mirrors
to prevent a portion of the optical system from blocking the area
through which the object light beam 104 passes, i.e., to separate a
principal ray of the object light beam 104 from an optical axis
105.
[0012] FIG. 38 is a schematic view of the mirror optical system
disclosed in U.S. Pat. No. 3,674,334. This mirror optical system
solves the above-described blocking problem by using part of
reflecting mirrors which are rotationally symmetrical about the
optical axis.
[0013] In the mirror optical system shown in FIG. 38, a concave
mirror 111, a convex mirror 113 and a concave mirror 112 are
arranged in the order of passage of the light beam, and these
mirrors 111, 113 and 112 are reflecting mirrors which are
rotationally symmetrical about an optical axis 114, as shown by
two-dot chain lines in FIG. 38. In the shown mirror optical system,
a principal ray 116 of an object light beam 115 is separated from
the optical axis 114 to prevent shading of the object light beam
115, by using only the upper portion of the concave mirror 111
which is above the optical axis 114 as viewed in FIG. 38, only the
lower portion of the convex mirror 113 which is below the optical
axis 114 as viewed in FIG. 38, and only the lower portion of the
concave mirror 112 which is below the optical axis 114 as viewed in
FIG. 38.
[0014] FIG. 39 is a schematic view of the mirror optical system
disclosed in U.S. Pat. No. 5,063,586. The shown mirror optical
system solves the above-described problem by decentering the
central axis of each reflecting mirror from an optical axis and
separating the principal ray of an object light beam from the
optical axis. As shown in FIG. 39 in which an axis perpendicular to
an object plane 121 is defined as an optical axis 127, a convex
mirror 122, a concave mirror 123, a convex mirror 124 and a concave
mirror 125 are arranged in the order of passage of the light beam,
and the central coordinates and central axes 122a, 123a, 124a and
125a (axes which respectively connect the centers of reflecting
surfaces and the centers of curvature thereof) of the reflecting
surfaces of the respective mirrors 122 to 125 are decentered from
the optical axis 127. In the shown mirror optical system, by
appropriately setting the amount of decentering and the radius of
curvature of each of the surfaces, each of the reflecting mirrors
is prevented from shading an object light beam 128, so that an
object image is efficiently formed on an image plane 126.
[0015] In addition, U.S. Pat. Nos. 4,737,021 and 4,265,510 also
disclose an arrangement for preventing the shading problem by using
part of a reflecting mirror which is rotationally symmetrical about
an optical axis, or an arrangement for preventing the shading
problem by decentering the central axis of the reflecting mirror
from the optical axis.
[0016] One example of a catadioptric optical system which uses both
a reflecting mirror and a refracting lens and has a magnification
varying function is a deep-sky telescope such as that disclosed in
each of U.S. Pat. Nos. 4,477,156 and 4,571,036. The deep-sky
telescope uses a parabolic reflecting mirror as a primary mirror
and has a magnification varying function using an Erfle
eyepiece.
[0017] Another variable magnification optical system is known which
varies the image forming magnification (focal length) of a
photographing optical system by relatively moving a plurality of
reflecting mirrors which constitute part of the aforesaid type of
mirror optical system.
[0018] For example, U.S. Pat. No. 4,812,030 discloses an art for
performing variation of the magnification of the photographing
optical system by relatively varying the distance between the
concave mirror 101 and the convex mirror 102 and the distance
between the convex mirror 102 and the image plane 103 in the
construction of the Cassegrainian reflecting telescope shown in
FIG. 37.
[0019] FIG. 40 is a schematic view of another embodiment disclosed
in U.S. Pat. No. 4,812,030. In the shown embodiment, an object
light beam 138 from an object is made incident on and reflected by
a first concave mirror 131, and travels toward an object side as a
converging light beam and is made incident on a first convex mirror
132. The light beam is reflected toward an image forming plane by
the first convex mirror 132 and is made incident on a second convex
mirror 134 as an approximately parallel light beam. The light beam
is reflected by the second convex mirror 134 and is made incident
on a second concave mirror 135 as a diverging light beam. The light
beam is reflected by the second concave mirror 135 as a converging
light beam and forms an image of the object on an image plane 137.
In this arrangement, by varying the distance between the first
concave mirror 131 and the first convex mirror 132 and the distance
between the second convex mirror 134 and the second concave mirror
135, zooming is performed and the focal length of the entire mirror
optical system is varied.
[0020] In the arrangement disclosed in U.S. Pat. No. 4,993,818, an
image formed by the Cassegrainian reflecting telescope shown in
FIG. 37 is secondarily formed by another mirror optical system
provided in a rear stage, and the magnification of the entire
photographing optical system is varied by varying the image forming
magnification of that secondary image forming mirror optical
system.
[0021] In any of the above-described reflecting types of
photographing optical systems, a large number of constituent
components are needed and individual optical components need to be
assembled with high accuracy to obtain the required optical
performance. Particularly since the relative position accuracy of
each of the reflecting mirrors is strict, it is indispensable to
adjust the position and the angle of each of the reflecting
mirrors.
[0022] One proposed approach to solving this problem is to
eliminate the incorporation error of optical components which
occurs during assembly, as by forming a mirror system as one
block.
[0023] A conventional example in which a multiplicity of reflecting
surfaces are formed as one block is an optical prism, such as a
pentagonal roof prism or a Porro prism, which is used in, for
example, a viewfinder optical system. In the case of such a prism,
since a plurality of reflecting surfaces are integrally formed, the
relative positional relationships between the respective reflecting
surfaces are set with high accuracy, so that adjustment of the
relative positions between the respective reflecting surfaces is
not needed. Incidentally, the primary function of the prism is to
reverse an image by varying the direction in which a ray travels,
and each of the reflecting surfaces consists of a plane
surface.
[0024] Another type of optical system, such as a prism having
reflecting surfaces with curvatures, is also known.
[0025] FIG. 41 is a schematic view of the essential portion of the
observing optical system which is disclosed in U.S. Pat. No.
4,775,217. This observing optical system is an optical system which
not only allows an observer to observe a scene of the outside but
also allows the observer to observe a display image displayed on an
information display part, in the form of an image which overlaps
the scene.
[0026] In this observing optical system, a display light beam 145
which exits from the display image displayed on an information
display part 141 is reflected by a surface 142 and travels toward
an object side and is made incident on a half-mirror surface 143
consisting of a concave surface. After having been reflected by the
half-mirror surface 143, the display light beam 145 is formed into
an approximately parallel light beam by the refractive power of the
half-mirror surface 143. This approximately parallel light beam is
refracted by and passes through a surface 142, and forms a
magnified virtual image of the display image and enters a pupil 144
of an observer so that the observer recognizes the display
image.
[0027] In the meantime, an object light beam 146 from an object is
incidence on a surface 147 which is approximately parallel to the
reflecting surface 142, and is then refracted by the surface 147
and reaches the half-mirror surface 143 which is a concave surface.
Since the concave surface 143 is coated with an evaporated
semi-transparent film, part of the object light beam 146 passes
through the concave surface 143, is refracted by and passes through
the surface 142, and enters the pupil 144 of the observer. Thus,
the observer can visually recognize the display image as an image
which overlaps the scene of the outside.
[0028] FIG. 42 is a schematic view of the essential portion of the
observing optical system disclosed in Japanese Laid-Open Patent
Application No. Hei 2-297516. This observing optical system is also
an optical system which not only allows an observer to observe a
scene of the outside but also allows the observer to observe a
display image displayed on an information display part, as an image
which overlaps the scene.
[0029] In this observing optical system, a display light beam 154
which exits from an information display part 150 passes through a
plane surface 157 which constitutes part of a prism Pa, and is made
incident on a parabolic reflecting surface 151. The display light
beam 154 is reflected by the reflecting surface 151 as a converging
light beam, and forms an image on a focal plane 156. At this time,
the display light beam 154 reflected by the reflecting surface 151
reaches the focal plane 156 while being totally reflected between
two parallel plane surfaces 157 and 158 which constitute part of
the prism Pa. Thus, the thinning of the entire optical system is
achieved.
[0030] Then, the display light beam 154 which exits from the focal
plane 156 as a diverging light beam is totally reflected between
the plane surface 157 and the plane surface 158, and is made
incident on a half-mirror surface 152 which consists of a parabolic
surface. The display light beam 154 is reflected by the half-mirror
surface 152 and, at the same time, not only is a magnified virtual
image of a display image formed but also the display light beam 154
is formed into an approximately parallel light beam by the
refractive power of the half-mirror surface 152. The obtained light
beam passes through the surface 157 and enters a pupil 153 of the
observer, so that the observer can recognize the display image.
[0031] In the meantime, an object light beam 155 from the outside
passes through a surface 158b which constitutes part of a prism Pb,
then through the half-mirror surface 152 which consists of a
parabolic surface, then through the surface 157, and is then made
incident on the pupil 153 of the observer. Thus, the observer
visually recognizes the display image as an image which overlaps
the scene of the outside.
[0032] As another example which uses an optical element on a
reflecting surface of a prism, optical heads for optical pickups
are disclosed in, for example, Japanese Laid-Open Patent
Application Nos. Hei 5-12704 and Hei 6-139612. In these optical
heads, after the light outputted from a semiconductor laser has
been reflected by a Fresnel surface or a hologram surface, the
reflected light is focused on a surface of a disk and the light
reflected from the disk is conducted to a detector.
[0033] However, in any of the aforesaid optical systems composed of
conventional refracting optical elements only, a stop is disposed
in the inside of the optical system, and an entrance pupil is in
many cases formed at a position deep in the optical system. This
leads to the problem that the larger the distance to a pupil plane
lying at a position which is the closest to the object side as
viewed from the stop, the effective ray diameter of the entrance
pupil becomes the larger with the enlargement of the angle of
view.
[0034] In any of the above-described mirror optical systems having
the decentered mirrors, which are disclosed in U.S. Pat. Nos.
3,674,334, 5,063,586 and 4,265,510, since the individual reflecting
mirrors are disposed with different amounts of decentering, the
mounting structure of each of the reflecting mirrors is very
complicated and the mounting accuracy of the reflecting mirrors is
very difficult to ensure.
[0035] In either of the above-described photographing optical
systems having the magnification varying functions, which are
disclosed in U.S. Pat. Nos. 4,812,030 and 4,993,818, since a large
number of constituent components, such as a reflecting mirror or an
image forming lens, are needed, it is necessary to assemble each
optical part with high accuracy to realize the required optical
performance.
[0036] In particular, since the relative position accuracy of the
reflecting mirrors is strict, it is necessary to adjust the
position and the angle of each of the reflecting mirrors.
[0037] As is known, conventional reflecting types of photographing
optical systems have constructions which are suited to a so-called
telephoto lens using an optical system having an entire large
length and a small angle of view. However, if a photographing
optical system which needs fields of view from a standard angle of
view to a wide angle of view is to be obtained, the number of
reflecting surfaces which are required for aberration correction
must be increased, so that a far higher component accuracy and
assembly accuracy are needed and the cost and the entire size of
the optical system tend to increase.
[0038] The above-described observing optical system disclosed in
U.S. Pat. No. 4,775,217 is realized as a small-sized observing
optical system which is composed of a plane refracting surface and
a concave half-mirror surface. However, the exit surface 142 for
the respective light beams 145 and 146 from the information display
part 141 and the outside needs to be used as a total reflecting
surface for the light beam 145 exiting from the information display
part 141, so that it is difficult to give a curvature to the
surface 142 and no aberration correction is effected at the exit
surface 142.
[0039] The above-described observing optical system disclosed in
Japanese Laid-Open Patent Application No. Hei 2-297516 is realized
as a small-sized observing optical system which is composed of a
plane refracting surface, a parabolic reflecting surface and a
half-mirror consisting of a parabolic surface. In this observing
optical system, the entrance surface 158 and the exit surface 157
for the object light beam 155 from the outside are formed to extend
so that their respective extending surfaces can be used as total
reflecting surfaces for guiding the light beam 154 which exits from
the information display part 150. For this reason, it is difficult
to give curvatures to the respective surfaces 158 and 157 and no
aberration correction is effected at either of the entrance surface
158 and the exit surface 157.
[0040] The range of applications of either of the optical systems
for optical pickups which are disclosed in, for example, Japanese
Laid-Open Patent Application Nos. Hei 5-12704 and Hei 6-139612 is
limited to the field of a detecting optical system, and neither of
them satisfies the image forming performance required for,
particularly, an image pickup apparatus which uses an area type of
image pickup device, such as a CCD.
BRIEF SUMMARY OF THE INVENTION
[0041] An object of the present invention is to provide a
high-performance variable magnification optical system which
includes a plurality of optical units two of which move relative to
each other to realize variation of the magnification of the
variable magnification optical system, the variable magnification
optical system being capable of varying the magnification while
varying the optical path length from an object to a final image
plane with the final image forming plane spatially fixed, so that
the thickness of the variable magnification optical system is small
in spite of its wide angle of view and its entire length is short
in a predetermined direction as well as its decentering aberration
is fully corrected over the entire range of variation of
magnification.
[0042] Another object of the present invention is to provide an
image pickup apparatus using the aforesaid high-performance
variable magnification optical system.
[0043] Another object of the present invention is to provide a
variable magnification optical system having at least one of the
following effects and advantages, and an image pickup apparatus
employing such a variable magnification optical system.
[0044] Since a stop is arranged on the object side of the variable
magnification optical system or in the vicinity of the first
surface and an object image is formed by a plurality of times in
the variable magnification optical system, the effective diameter
and the thickness of the variable magnification optical system can
be made small in spite of its wide angle of view.
[0045] Since each optical unit employs an optical element having a
plurality of reflecting surfaces having appropriate refractive
powers and the reflecting surfaces are arranged in a decentered
manner, the optical path in the variable magnification optical
system can be bent into a desired shape to reduce the entire length
of the variable magnification optical system in a predetermined
direction.
[0046] A plurality of optical elements which constitute the
variable magnification optical system are each formed as a
transparent body on which two refracting surfaces and a plurality
of reflecting surfaces are integrally formed in such a manner that
each of the reflecting surfaces is arranged in a decentered manner
and is given an appropriate refractive power. Accordingly, the
decentering aberration of the variable magnification optical system
can be fully corrected over the entire range of variation of
magnification.
[0047] Since each magnification varying optical unit employs an
optical element which is formed as a transparent body on which two
refracting surfaces and a plurality of curved or plane reflecting
surfaces are integrally formed, not only is it possible to reduce
the entire size of the variable magnification optical system, but
it is also possible to solve the problem of excessively strict
arrangement accuracy (assembly accuracy) which would have often
been experienced with reflecting surfaces.
[0048] A variator optical unit which shows a largest amount of
variation of magnification during a magnification varying operation
is fixed, and an optical unit lying on the object side of the
variator optical unit is moved to vary the magnification of the
variable magnification optical system, so that an exit pupil on its
telephoto side can be formed at a position more distant from an
image plane than that on its wide-angle side. Accordingly, by
appropriately setting the position of the exit pupil at the
wide-angle end, it is possible to restrain occurrence of shading
over the entire range of variation of magnification in an image
pickup apparatus employing a solid-state image pickup device.
[0049] A variator optical unit which shows a largest amount of
variation of magnification during a magnification varying operation
is composed of an optical element having an entering reference axis
and an exiting reference axis which differ from each other by
180.degree. in direction. The variator optical unit is fixed, and
an optical unit lying on the object side of the variator optical
unit is moved to vary the magnification of the variable
magnification optical system, so that the distance of movement of a
moving optical unit positioned on the image-plane side of the
variator optical unit can be reduced.
[0050] To achieve the above objects, in accordance with one aspect
of the present invention, there is provided a variable
magnification optical system which comprises at least three optical
units, the three optical units being a first moving optical unit, a
fixed optical unit and a second moving optical unit which are
arranged in that order in a propagation direction of light, a
variation of magnification being effected by a relative movement
between the first moving optical unit and the second moving optical
unit, wherein if a ray which exits from an object and enters the
variable magnification optical system, and passes through a center
of a stop of the variable magnification optical system and reaches
a center of a final image plane is represented as a reference axis
ray; a reference axis ray which is incident on any surface of the
variable magnification optical system or enters any of the optical
units is represented as an entering reference axis of the aforesaid
any surface or the aforesaid any optical unit; a reference axis ray
which exits from the aforesaid any surface or the aforesaid any
optical unit is represented as an exiting reference axis of the
aforesaid any surface or the aforesaid any optical unit; a point at
which the entering reference axis intersects with the aforesaid any
surface is represented as a reference point; a direction in which
the reference axis ray travels from an object side toward an image
plane along the entering reference axis is represented as a
direction of the entering reference axis; and a direction in which
the reference axis ray travels from the object side toward the
image plane along the exiting reference axis is represented as a
direction of the exiting reference axis, the second moving optical
unit has a cross-sectional shape which is asymmetrical in a plane
which contains the reference axis, and a curved reflecting surface
which is inclined with respect to the reference axis, and the
direction of the entering reference axis and the direction of the
exiting reference axis of the second moving optical unit are
parallel to each other and differ from each other by 180 .degree.,
the variable magnification optical system being arranged in such a
manner that a final image is formed after an intermediate image is
formed at least twice.
[0051] In the variable magnification optical system, the fixed
optical unit is an optical unit having the largest ratio of (a
lateral magnification at a wide-angle end) to (a lateral
magnification at a telephoto end) of all the optical units.
[0052] In the variable magnification optical system, the first
moving optical unit moves toward the fixed optical unit during a
variation of magnification from a wide-angle end toward a telephoto
end.
[0053] In the variable magnification optical system, the second
moving optical unit includes an optical element which is formed as
one transparent body on which two refracting surfaces and a
plurality of internal curved reflecting surfaces are formed.
[0054] In the variable magnification optical system, the first
moving optical unit includes an optical element which is formed as
one transparent body on which two refracting surfaces and a
plurality of internal curved reflecting surfaces inclined with
respect to the reference axis are formed, the direction of the
entering reference axis and the direction of the exiting reference
axis of the optical element being parallel to and the same as each
other.
[0055] In the variable magnification optical system, the first
moving optical unit includes an optical element which is formed as
one transparent body on which two refracting surfaces and a
plurality of internal curved reflecting surfaces inclined with
respect to the reference axis are formed, the direction of the
entering reference axis and the direction of the exiting reference
axis of the optical element being parallel to each other and
different from each other by 180.degree..
[0056] In the variable magnification optical system, the first
moving optical unit forms an intermediate image in its inside.
[0057] In the variable magnification optical system, the fixed
optical unit includes an optical element which is formed as one
transparent body on which two refracting surfaces and a plurality
of internal curved reflecting surfaces inclined with respect to the
reference axis are formed, the direction of the entering reference
axis and the direction of the exiting reference axis of the optical
element being parallel to and the same as each other.
[0058] In the variable magnification optical system, the fixed
optical unit includes an optical element which is formed as one
transparent body on which two refracting surfaces and a plurality
of internal curved reflecting surfaces inclined with respect to the
reference axis are formed, the direction of the entering reference
axis and the direction of the exiting reference axis of the optical
element being parallel to each other and different from each other
by 180.degree..
[0059] In the variable magnification optical system, the fixed
optical unit includes an optical element which is formed as one
transparent body on which two refracting surfaces and a plurality
of internal curved reflecting surfaces inclined with respect to the
reference axis are formed, the exiting reference axis of the
optical element being inclined with respect to the entering
reference axis thereof.
[0060] In the variable magnification optical system, the stop is
located on the object side of the first moving optical unit, the
stop being fixed during the variation of magnification.
[0061] In accordance with another aspect of the present invention,
there is provided a variable magnification optical system which
comprises a fixed optical unit and a plurality of magnification
varying optical units which are arranged in that order in a
propagation direction of light, a variation of magnification being
effected by a relative movement between the plurality of
magnification varying optical units, wherein letting f.sub.i be a
focal length of any magnification varying optical unit i and
letting k be a number of times by which an on-axial light beam
forms an intermediate image in the aforesaid any magnification
varying optical unit i, the aforesaid any magnification varying
optical unit i satisfies:
[0062] f.sub.i.multidot.(-1).sup.k>0 (k is an integer not less
than 0), and wherein if a ray which exits from an object and enters
the variable magnification optical system, and passes through a
center of a stop of the variable magnification optical system and
reaches a center of a final image plane is represented as a
reference axis ray; a reference axis ray which is incident on any
surface of the variable magnification optical system or enters any
of the optical units is represented as an entering reference axis
of the aforesaid any surface or the aforesaid any optical unit; a
reference axis ray which exits from the aforesaid any surface or
the aforesaid any optical unit is represented as an exiting
reference axis of the aforesaid any surface or the aforesaid any
optical unit; a point at which the entering reference axis
intersects with the aforesaid any surface is represented as a
reference point; a direction in which the reference axis ray
travels from an object side toward an image plane along the
entering reference axis is represented as a direction of the
entering reference axis; and a direction in which the reference
axis ray travels from the object side toward the image plane along
the exiting reference axis is represented as a direction of the
entering reference axis, any of the magnification varying optical
units includes at least one concave reflecting surface the entering
and exiting reference axes of which are inclined with respect to a
normal to the concave reflecting surface at the reference point
thereof, the concave reflecting surface having a cross-sectional
shape which is asymmetrical in a plane which contains the entering
reference axis and the exiting reference axis.
[0063] The above and other objects, features and advantages of the
present invention will become apparent from the following detailed
description of preferred embodiments as well as numerical examples,
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0064] FIG. 1 is a view of the optical arrangement of a first
embodiment of the variable magnification optical system according
to the present invention;
[0065] FIG. 2 is an explanatory view showing the first embodiment
in the form of a coaxial system;
[0066] FIGS. 3(A) and 3(B) are explanatory views of an exit pupil
distance of the first embodiment;
[0067] FIG. 4 is a view of the optical arrangement of a second
embodiment of the variable magnification optical system according
to the present invention;
[0068] FIG. 5 is a view of the optical arrangement of a third
embodiment of the variable magnification optical system according
to the present invention;
[0069] FIG. 6 is a view of the optical arrangement of a fourth
embodiment of the variable magnification optical system according
to the present invention;
[0070] FIG. 7 is an explanatory view showing the fourth embodiment
in the form of a coaxial system;
[0071] FIG. 8 is a view of the optical arrangement of the variable
magnification optical system according to the present
invention;
[0072] FIG. 9 is a view of an example of the arrangement of an
optical unit which constitutes part of the variable magnification
optical system according to the present invention;
[0073] FIG. 10 is a perspective view showing one example of the
variable magnification optical system according to the present
invention;
[0074] FIG. 11 is a view of one example of the arrangement of
another optical unit which constitutes part of the variable
magnification optical system according to the present
invention;
[0075] FIG. 12 is an explanatory view of a coordinate system for
Numerical Examples 1 to 3 of the present invention;
[0076] FIG. 13 is an optical cross-sectional view of Numerical
Example 1 relative to its wide-angle end;
[0077] FIG. 14 is an optical cross-sectional view of Numerical
Example 1 relative to its middle position;
[0078] FIG. 15 is an optical cross-sectional view of Numerical
Example 1 relative to its telephoto end;
[0079] FIG. 16 is a lateral aberration chart of Numerical Example 1
relative to the wide-angle end;
[0080] FIG. 17 is a lateral aberration chart of Numerical Example 1
relative to the middle position;
[0081] FIG. 18 is a lateral aberration chart of Numerical Example 1
relative to the telephoto end;
[0082] FIG. 19 is an optical cross-sectional view of Numerical
Example 2 relative to its wide-angle end;
[0083] FIG. 20 is an optical cross-sectional view of Numerical
Example 2 relative to its middle position;
[0084] FIG. 21 is an optical cross-sectional view of Numerical
Example 2 relative to its telephoto end;
[0085] FIG. 22 is a lateral aberration chart of Numerical Example 2
relative to the wide-angle end;
[0086] FIG. 23 is a lateral aberration chart of Numerical Example 2
relative to the middle position;
[0087] FIG. 24 is a lateral aberration chart of Numerical Example 2
relative to the telephoto end;
[0088] FIG. 25 is an optical cross-sectional view of Numerical
Example 3 relative to its wide-angle end;
[0089] FIG. 26 is an optical cross-sectional view of Numerical
Example 3 relative to its middle position;
[0090] FIG. 27 is an optical cross-sectional view of Numerical
Example 3 relative to its telephoto end;
[0091] FIG. 28 is a lateral aberration chart of Numerical Example 3
relative to the wide-angle end;
[0092] FIG. 29 is a lateral aberration chart of Numerical Example 3
relative to the middle position;
[0093] FIG. 30 is a lateral aberration chart of Numerical Example 3
relative to the telephoto end;
[0094] FIG. 31 is a view showing one example of an off-axial
optical system;
[0095] FIG. 32 is a view showing a representation method used in
the present invention, with its origin at the intersection of a
surface and a reference axis of the off-axial optical system;
[0096] FIG. 33 is a view showing a coordinate system for a paraxial
expansion to be performed along a bent reference axis, and various
quantities for use in the paraxial expansion;
[0097] FIG. 34 is a view showing the decomposition of an image
point vector into components;
[0098] FIG. 35 is a view showing the principal point, the focus and
the focal length of the off-axial optical system;
[0099] FIG. 36 is a view showing an off-axial reflecting quadratic
curved surface having two focal points through which the reference
axis passes;
[0100] FIG. 37 is a view of the basic arrangement of a
Cassegrainian reflecting telescope;
[0101] FIG. 38 is an explanatory view showing a first method of
preventing shading by shifting a principal ray from the optical
axis of a mirror optical system;
[0102] FIG. 39 is an explanatory view showing a second method of
preventing shading by shifting a principal ray from the optical
axis of a mirror optical system;
[0103] FIG. 40 is an conceptual diagram of a zoom optical system
employing conventional reflecting mirrors;
[0104] FIG. 41 is an conceptual diagram of an observing optical
system whose prism has a reflecting surface having a curvature;
[0105] FIG. 42 is an conceptual diagram of another observing
optical system whose prism has a reflecting surface having a
curvature;
[0106] FIG. 43 is an explanatory view showing the variable
magnification optical system according to the present invention in
the form of a coaxial refracting system;
[0107] FIG. 44 is a view showing the optical arrangement of a fifth
embodiment according to the present invention;
[0108] FIG. 45 is a view showing one basic arrangement of a
magnification varying optical unit of the variable magnification
optical system according to the present invention in the form of a
coaxial refracting system;
[0109] FIG. 46 is an explanatory view showing another basic
arrangement of the magnification varying optical unit of the
variable magnification optical system according to the present
invention in the form of a coaxial refracting system;
[0110] FIGS. 47(A) and 47(B) are explanatory views of the basic
arrangement of the magnification varying optical unit of the
variable magnification optical system according to the present
invention;
[0111] FIGS. 48(A) and 48(B) are views of the basic arrangement of
the magnification varying optical unit of the variable
magnification optical system according to the present
invention;
[0112] FIG. 49 is a view showing an arrangement of the fifth
embodiment of the variable magnification optical system according
to the present invention;
[0113] FIG. 50 is a view showing another arrangement of the fifth
embodiment of the variable magnification optical system according
to the present invention;
[0114] FIG. 51 is a perspective view showing the essential portion
of one example of the variable magnification optical system
according to the present invention;
[0115] FIG. 52 is an explanatory view of a coordinate system for
Numerical Examples 4 to 6 of the present invention;
[0116] FIG. 53 is an optical cross-sectional view of Numerical
Example 4 of the variable magnification optical system of the
present invention with respect to its wide-angle end;
[0117] FIG. 54 is an optical cross-sectional view of Numerical
Example 4 relative to its middle position;
[0118] FIG. 55 is an optical cross-sectional view of Numerical
Example 4 relative to its telephoto end;
[0119] FIG. 56 is a lateral aberration chart of Numerical Example 4
relative to the wide-angle end;
[0120] FIG. 57 is a lateral aberration chart of Numerical Example 4
relative to the middle position;
[0121] FIG. 58 is a lateral aberration chart of Numerical Example 4
relative to the telephoto end;
[0122] FIG. 59 is an optical cross-sectional view of Numerical
Example 5 of the variable magnification optical system of the
present invention with respect to its wide-angle end;
[0123] FIG. 60 is an optical cross-sectional view of Numerical
Example 5 relative to its middle position;
[0124] FIG. 61 is an optical cross-sectional view of Numerical
Example 5 relative to its telephoto end;
[0125] FIG. 62 is a lateral aberration chart of Numerical Example 5
relative to the wide-angle end;
[0126] FIG. 63 is a lateral aberration chart of Numerical Example 5
relative to the middle position;
[0127] FIG. 64 is a lateral aberration chart of Numerical Example 5
relative to the telephoto end;
[0128] FIG. 65 is an explanatory view showing a method of changing
the direction of the reference axis by using a prism as the second
optical element of Numerical Example 5;
[0129] FIG. 66 is an optical cross-sectional view of Numerical
Example 6 of the variable magnification optical system of the
present invention with respect to its wide-angle end;
[0130] FIG. 67 is an optical cross-sectional view of Numerical
Example 6 relative to its middle position;
[0131] FIG. 68 is an optical cross-sectional view of Numerical
Example 6 relative to its telephoto end;
[0132] FIG. 69 is a perspective view of the magnification varying
optical unit of Numerical Example 6;
[0133] FIG. 70 is a lateral aberration chart of Numerical Example 6
relative to its wide-angle end;
[0134] FIG. 71 is a lateral aberration chart of Numerical Example 6
relative to the middle position;
[0135] FIG. 72 is a lateral aberration chart of Numerical Example 6
relative to the telephoto end; and
[0136] FIG. 73 is an explanatory view showing a method of changing
the direction of the reference axis by using a prism as the first
optical element of Numerical Example 6.
DETAILED DESCRIPTION OF THE INVENTION
[0137] The variable magnification optical system according to the
present invention is a so-called decentered optical system
(off-axial optical system) which employs decentered reflecting
surfaces. Such a decentered optical system does not have an optical
axis common to each of the reflecting surfaces, and this leads to
the problem that no general paraxial calculations can be used. For
this reason, the present invention introduces the concept of a
reference axis which is equivalent to the optical axis of a coaxial
optical system, and is intended to design the decentered optical
system by developing a paraxial theory with respect to such
reference axis. The paraxial theory of the decentered optical
system (herein referred to also as the off-axial optical system)
will be described below.
[0138] <Paraxial theory of the off-axial optical system>
[0139] 1. Method of representing the off-axial optical system and
its constituent surfaces.
[0140] 1-1. Off-axial optical system
[0141] The off-axial optical system and the reference axis which
constitutes the skeleton of the off-axial optical system will be
defined hereinbelow in contrast with a conventional coaxial optical
system which has been widely used.
[0142] a) Definition of the reference axis
[0143] In general, the "reference axis" in an optical system is
defined as an optical path along which a particular reference ray
having a reference wavelength travels from an object plane to an
image plane. Since the reference ray is not yet determined in this
definition, a reference axis ray is determined normally in
accordance with either of the following two principles.
[0144] (1) If an axis having symmetry which is even partial is
present in an optical system and correction of aberration can be
effected with sufficient symmetry, a ray which passes along the
axis having symmetry is determined as the reference axis ray.
[0145] (2) If an axis is generally absent in an optical system or
if a symmetrical axis is partly present but correction of
aberration can not be effected with sufficient symmetry, a ray
which comes from the center of an object plane (the center of the
area of a scene being observed photographed) and passes through the
center of the stop provided in the optical system after having
sequentially passed through specified surfaces in the optical
system, or a ray which passes through the center of the stop
provided in the optical system and reaches the center of a final
image plane is determined as the reference axis ray, and the
optical path of the reference axis ray is determined as the
reference axis.
[0146] The reference axis defined in the above-described manner
generally has a bent shape.
[0147] (Refer to FIG. 31.)
[0148] In FIG. 31, it is assumed that each surface has a reference
point which is the intersection of the surface and a reference axis
ray, and that the reference axis rays located on the object and
image sides of each surface are called an entering reference axis
and an exiting reference axis, respectively. In addition, the
reference axis has a direction, and the direction is a direction in
which the reference axis ray travels to form an image. Therefore,
the direction of the entering reference axis and the direction of
the exiting reference axis are present on the entrance and exit
sides of each surface, respectively. The reference axis is
refracted by individual surfaces in a predetermined order thereof,
or changes its direction in accordance with the law of reflection,
and finally reaches an image plane.
[0149] If an optical element (optical system) includes a plurality
of surfaces, a reference axis ray which is made incident on a
surface closest to the object side is defined as the entering
reference axis of the optical element (optical system), and a
reference axis ray which exits from a surface closest to the image
side is defined as the exiting reference axis of the optical
element (optical system).
[0150] b) Definition of off-axial optical system
[0151] The off-axial optical system is defined as an optical system
which includes a curved surface (off-axial curved surface) whose
surface normal do not coincide with the above-defined reference
axis at a point where the reference axis intersects with the curved
surface. FIG. 31 shows one example of the off-axial optical system.
(If the reference axis is simply bent by a plane reflecting
surface, the reference axis does not coincide with its surface
normal, but since the plane reflecting surface does not impair the
symmetry of aberration, this case is excluded from the definition
of the off-axial optical system.)
[0152] This definition also includes an optical system having a
coaxial optical system which is partly decentered to a great
extent. However, a dot or a line which has symmetry representative
of the "center" of "decentering" is in general absent in an optical
system composed of asymmetrical aspheric surfaces. For this reason,
the present paraxial theory avoids using the term "decentering",
and uses the term "off-axial".
[0153] 1-2. Shape-of-surface representing method suited to the
constituent surfaces of the off-axial optical system
[0154] In general, surfaces which constitute the off-axial optical
system do not have symmetry. The most general method of
representing a surface having no symmetry is an expansion into
power series in two variables relative to the center of the
expansion. The center of the expansion is herein defined as the
intersection of a surface and a reference axis, and the z axis of a
local coordinate system which expresses the shape of the surface
corresponds to the surface normal thereof. An equation which
represents the shape is expressed in the form of z=f(x, y).
Expansion of the equation is started at degree 2 in the following
manner so that the surface normal at that intersection point does
not vary with a variation in the shape of the surface: 1 z ( x , y
) = C 20 x 2 + 2 C 11 xy + C 02 y 2 + D 30 x 3 + 3 D 21 x 2 y + 3 D
12 xy 2 + D 03 y 3 + E 40 x 4 + 4 E 31 x 3 y + 6 E 22 x 2 y 2 + 4 E
13 xy 3 + E 04 y 4 + (Equation1)
[0155] By defining each constituent surface by using the method of
performing an expansion with a surface normal fixed at a reference
point in the above-described manner, it is possible to vary the
shape of each surface without changing the skeleton of the entire
optical arrangement (the layout of the reference axis), as shown in
FIG. 32, unlike a conventional method of designing an off-axial
optical system. Furthermore, if the first- and second-degree
coefficients are fixed and the third-degree coefficient as well as
coefficients of degrees higher than the third degree are varied, it
is possible to effect only correction of aberration without
changing a paraxial quantity for each azimuth (refer to the results
of Equations (8) to (11) which will be described later).
[0156] 2. Method of performing a paraxial expansion along a bent
reference axis.
[0157] FIG. 33 shows a coordinate system for a paraxial expansion
to be performed along a bent reference axis, and various quantities
for use in an analysis which uses the coordinate system. Since
reflection can be generalized as refraction of negative refractive
index, the expansion is assumed to be performed on the basis of a
refracting optical system. In FIG. 33, local coordinate systems are
defined along the reference axis at the portions of an object and
an image, and an object plane, an image plane, an entrance pupil
plane and an exit pupil plane are defined perpendicularly to the
reference axis as shown in FIG. 33. The shape of a surface is
represented by a local coordinate system whose z axis corresponds
to its surface normal, as described previously. It is assumed here
that a ray passes through an object-line vector b and a height
vector r in an entrance pupil, and the law of refraction is
expanded into power series on the condition that the object-line
vector b and the height vector r have infinitesimal quantities. The
procedure is as follows.
[0158] i) A direction vector s of the ray is expressed by using the
distance s shown in FIG. 33, an absolute value b of the object-line
vector b, an azimuth .xi. of the object-line vector b (.xi.=0 at a
refracting surface which refracts the reference axis), a distance
t, an absolute value r of the height vector r, and
.xi..sub.r=.xi.+.phi. (the azimuth of the height vector r; .phi. is
a relative azimuth).
[0159] ii) An intersection at the refracting surface is obtained by
using the starting-point vector and the direction vector obtained
in i) as well as the equation which expresses the shape of the
surface.
[0160] iii) A surface-normal vector n at the intersection obtained
in ii) is obtained by a vector analysis method.
[0161] iv) A direction vector s' of the ray refracted at the
intersection is obtained by using the result of iii) and the law of
refraction.
[0162] v) Since the position of the intersection at the refracting
surface and the direction vector s' of the refracted ray are
obtained, if distances s' and t' are given, an image-line vector b'
and a height vector r' in an exit pupil are obtained.
[0163] The results of the first-degree expansion of the distance b'
of the image-line vector b' and the absolute value r of the height
vector r are expressed as Equations 2 and 3. Incidentally, .xi.' is
an ideal azimuth of the image line in the image plane and is taken
as .xi.'=.xi.. 2 r; = r ( s ( cos ' cos ' cos ( + ) + cos sin ' sin
( + ) ) / ( cos ( s - t ) ) - s ' N ( cos ' sin ' sin ( + ) + cos
cos ' cos ( + ) ) / ( N ' cos ' ( s - t ) ) - 2 ss ' ( N ' cos ' -
N cos ) { cos ' cos ( + ) C 02 + ( cos ' sin ' cos ( + ) + cos cos
' sin ( + ) ) C 11 + cos cos ' sin ' sin ( + ) C 20 } / ( N ' cos
cos ' ( s - t ) ) ) - b ( + t ( cos ' cos ' cos + cos sin ' sin ) /
( cos ( s - t ) ) - s ' N ( cos ' sin ' sin + cos cos ' cos ) / ( N
' cos ' ( s - t ) ) - 2 ts ' ( N ' cos ' - N cos ) { cos ' cos C 02
+ ( cos ' sin ' cos + cos cos ' sin ) C 11 + cos cos ' sin ' sin C
20 } / ( N ' cos cos ' ( s - t ) ) ) (Equation2) = r; / ' = r ( s (
- cos ' sin ' cos ( + ) + cos cos ' sin ( + ) ) / ( cos ( s - t ) )
- s ' N ( cos ' cos ' sin ( + ) - cos sin ' cos ( + ) ) / ( N ' cos
' ( s - t ) ) - 2 ss ' ( N ' cos ' - N cos ) { - sin ' cos ( + ) C
02 + ( cos ' cos ' cos ( + ) - cos sin ' sin ( + ) ) C 11 + cos cos
' cos sin ( + ) C 20 } / ( N ' cos cos ' ( s - t ) ) ) - b ( t ( -
cos ' sin ' cos + cos cos ' sin ) / ( cos ( s - t ) ) - s ' N ( cos
' cos ' sin - cos sin ' cos ) / ( N ' cos ' ( s - t ) ) - 2 ts ' (
N ' cos ' - N cos ) { - sin ' cos C 02 + ( cos ' cos ' cos - cos
sin ' sin ) C 11 + cos cos ' cos ' sin C 20 } / ( N ' cos cos ' ( s
- t ) ) ) (Equation3)
[0164] In this result, the image-line vector b' is decomposed into
components, as shown in FIG. 34, in the form expressed as:
b'=.beta.b+.DELTA..vertline..vertline.+.DELTA..perp., (Equation
4)
[0165] where .beta.b+.DELTA..vertline..vertline. represents a
parallel-component vector relative to the azimuth .xi. (.beta. is a
lateral magnification of a projection determined by Equation 11
which will be described later), and .DELTA..perp. represents a
vertical-component vector.
[0166] 3. Derivation of an image forming equation for the off-axial
optical system and paraxial quantities for refraction
[0167] 3-1 Derivation of an image forming equation for the
off-axial optical system
[0168] If a paraxial relation is to be obtained by using the
results of Equations 2 and 3, the object height b="0" may be put.
Accordingly, the first-degree proportional coefficients of r of
.DELTA..vertline..vertline- . and .DELTA..perp. may be examined.
However, since the paraxial ray lies at a skew position with
respect to the reference axis owing to the rotational asymmetry of
the optical system, those two coefficients depend on the azimuth
.xi. and, in general, the two coefficients cannot be made "0" at
the same time. In general, in the case of an anamorphic optical
system in which a paraxial ray lies at a skew position with respect
to a reference axis, an image forming conjugate relation and
paraxial quantities are defined from the coefficient of
.DELTA..vertline..vertline- .=0 of an optical path projected on an
azimuth cross section, and the image forming conjugate relation is
obtained from the equation of (the coefficient of
.DELTA..vertline..vertline.=0) with respect to .DELTA..perp..
However, the equation of this coefficient indicates that, in
general, a ray of relative azimuth .phi.=0 (which corresponds to a
meridional ray) and a ray of .phi.=.pi./2 (which corresponds to a
sagittal ray) differ from each other in image forming position (the
optical system has a so-called astigmatism).
[0169] Regarding this astigmatism on the reference axis, the
present theory defines an image forming plane for the relative
azimuth .phi.=0 as a paraxial image plane, and is constructed on
the assumption that an on-axial astigmatism remains in the case of
.phi..noteq.0. The following image forming relation projected on
the basis of the definition of such image plane is obtained: 3 N '
( cos ' cos ' cos + cos sin ' sin ) / ( s ' cos ) - N ( cos ' sin '
sin + cos cos ' cos ) / ( s cos ' ) - 2 ( N ' cos ' - N cos ) { cos
' cos C 02 + ( cos ' sin ' cos + cos cos ' sin ) C 11 + cos cos '
sin ' sin C 20 } / ( cos cos ' ) = 0. (Equation5)
[0170] Equation 5 can be changed into an image forming equation for
a pupil plane by replacing s and s' with t and t'. Accordingly, it
is apparent that the above image forming equation is a rational
definition which is the generalization of a conventional coaxial
optical system.
[0171] 3-2 Derivation of paraxial quantities of a refracting
surface and the expression of an equation for refraction using
Gaussian brackets
[0172] The projected image forming relation is compared with the
following image forming equation for a conventional coaxial optical
system:
(N.dbd.A)/s'-(ND)/S-.phi.=0, (Equation 6)
[0173] where A and D represent the diagonal elements of Gaussian
brackets for refraction, which are expressed as: 4 [ h ' ' ] = [ A0
D ] [ h ] , (Equation7)
[0174] and .PHI. represents power (in the case of a component B=0
and AD=1).
[0175] As is readily understood, since the equations 5 and 6 have
completely the same form, it is possible to determine the paraxial
quantities of an off-axial refracting surface which corresponds to
the image forming equation 6 by comparing Equations 5 and 6.
Specifically, with a projection of a paraxial ray, it is possible
to calculate a paraxial quantity for each azimuth similarly to that
in the coaxial optical system. The results of A, D and .PHI. are
shown as Equations 8 to 10. 5 A = cos ' ( cos ' cos ' cos + cos sin
' sin ) cos ( cos ' sin ' sin + cos cos ' cos ) (Equation8) D = 1 /
A = cos ( cos ' sin ' sin + cos cos ' cos ) cos ' ( cos ' cos ' cos
+ cos sin ' sin ) (Equation9) = 2 ( N ' cos ' - N cos ) { cos ' cos
C 02 + ( cos ' sin ' cos + cos cos ' sin ) C 11 + cos cos ' sin '
sin C 20 } cos cos ' ( cos ' cos ' cos + cos sin ' sin ) ( cos '
sin ' sin + cos cos ' cos ) (Equation10)
[0176] The lateral magnification of projection at the refracting
surface may also be given by:
.beta.=.alpha./.alpha.'=Ns'D/(N's). (Equation 11)
[0177] It is to be noted that the paraxial quantities shown by
Equations 8 to 11 are a generalization of the paraxial quantities
of the conventional coaxial optical system. This can readily be
confirmed from the fact that Equations for the coaxial optical
system can be obtained by substituting conditions for coaxial
rotational symmetry, i.e., .theta.=.theta.'=0, C.sub.11=0,
C.sub.20=C.sub.02=1/(2R) (R: radius of curvature), for Equations 8
to 11.
[0178] 4. Paraxial tracing
[0179] 4-1 Guassian brackets for transfer
[0180] Although the paraxial quantities for refraction can be
defined by the method employing the Gaussian brackets with respect
to each surface of the off-axial optical system in the
above-described manner, it is necessary to define a
surface-to-surface transfer term for an optical system composed of
a plurality of surfaces. As is apparent from a simple geometrical
consideration, if a length d' is defined along the reference axis
of the off-axial optical system, the off-axial optical system can
be expressed in the form of the following Gaussian brackets by
using the converted surface-to-surface distance e'=d'/N', similarly
to the conventional coaxial optical system: 6 [ 1 - e ' 0 1 ] .
(Equation12)
[0181] Accordingly, even in the case of an optical system including
a plurality of off-axial surfaces, paraxial tracing for each
azimuth can be performed similarly to that in the conventional
coaxial optical system. In other words, the skeleton of the entire
off-axial optical system can be paraxially analyzed similarly to
that of the coaxial optical system.
[0182] 4-2 Method of paraxial tracing
[0183] Paraxial tracing similar to that for the coaxial optical
system can be performed by using the equations for refraction
obtained in 3-2:
h.sub.i'=A.sub.i.multidot.h.sub.i, (Equation 13)
.alpha..sub.i'=.PHI..sub.i.multidot.h.sub.i+D.sub.i.multidot..alpha..sub.i-
, (Equation 14)
[0184] and the equations for transfer obtained in 4-1:
h.sub.i+1=h.sub.i'e.sub.i'.multidot..alpha..sub.i', (Equation
15)
.alpha..sub.i+1=.alpha..sub.i'. (Equation 16)
[0185] The off-axial optical system differs from the coaxial
optical system in that, in the equations for refraction, A.sub.i
and D.sub.i generally are not "1" and A.sub.i, D.sub.i and
.PHI..sub.I have azimuth dependence. Accordingly, if a paraxial
quantity for each azimuth is calculated, the azimuth dependence of
the paraxial quantity can be examined.
[0186] The flow of performing calculations on paraxial tracing
relative to a given azimuth .xi. is shown below.
[0187] i) Initial values h.sub.1 and .alpha..sub.1
(.alpha..sub.1=N.sub.1h- .sub.1/s.sub.1) for paraxial tracing are
set with respect to given data for an optical system, such as
s.sub.1.
[0188] ii) The paraxial quantities A.sub.i, .PHI..sub.i and D.sub.i
of a refracting surface are obtained.
[0189] iii) The equations for refraction are used to obtain
h.sub.i' and .alpha..sub.i'.
[0190] If necessary, s.sub.i and s.sub.i' and a lateral
magnification .beta..sub.i at the refracting surface are obtained
by using the following equations:
s.sub.i=N.sub.i-h.sub.i/.alpha..sub.i, (Equation 17)
s.sub.i'=N.sub.i'h.multidot.h.sub.i'/.alpha..sub.i', (Equation
18)
.beta..sub.i=.alpha..sub.i/.alpha..sub.i'. (Equation 19)
[0191] iv) If the surface number i is not that of a final surface,
the equations for transfer are used to obtain h.sub.i+1 and
.alpha..sub.i+1.
[0192] v) Steps ii) to iv) are repeated until the number i reaches
a number k of the final surface.
[0193] vi) The components A, B, .PHI. and D of the Guassian
brackets for the entire optical system are obtained so that
h.sub.k' and .alpha..sub.k' obtained from the above equations when
the surface number i is the final surface number k can satisfy the
following equations at all times:
h.sub.k'=Ah.sub.1+B.alpha..sub.1, (Equation 20)
.alpha..sub.k'=.phi.h.sub.1+D.alpha..sub.i. (Equation 21)
[0194] vii) The obtained components A, B, .phi. and D for the
entire optical system are employed to obtain a focal length f, the
positions of principal points H and H' and a back focus s.sub.k' by
using equations similar to those used for the coaxial optical
system:
f=1/.PHI., (Equation 22)
.DELTA..sub.1=(1-D)/.PHI., H=N.sub.1.DELTA..sub.1, (Equation
23)
.DELTA..sub.k'=(A-1)/.PHI., H'=N.sub.k'.DELTA..sub.k', (Equation
24)
s.sub.k'=N.sub.k'(f+.DELTA..sub.k'). (Equation 25)
[0195] (Refer to FIG. 35. In FIG. 35, F represents a focus on an
object side, H represents a principal point on the object side, F'
represents a focus on an image side, and H' represents a principal
point on the image side.)
[0196] viii) The lateral magnification .beta. of the entire optical
system is obtained by:
.beta.=.alpha..sub.1/.DELTA..sub.k'. (Equation 26)
[0197] 5. Analysis and confirmation using simple surfaces
[0198] The method of applying the obtained paraxial theory to
simple surfaces will be described below.
[0199] a) Off-axial reflecting surface
[0200] Since .theta.=-.theta.' in the off-axial reflecting system,
each of A and D of the Gaussian brackets is "1", i.e., the same as
those of the coaxial optical system. In this case, the off-axial
reflecting surface has an anamorphic power which depends on a
curvature, the angle of incidence .theta., and the azimuth .xi..
Furthermore, if the coefficients C.sub.20, C.sub.11 and C.sub.02 of
the shape of the surface, which are proportional to the curvature,
are selected to satisfy:
C.sub.11=0, C.sub.02=C.sub.20cos.sup.2.theta., (Equation 27)
[0201] the power of the reflecting surface does not depend on the
azimuth .xi..
[0202] In other words, if the coefficients of the shape of the
surface relative to the x and y directions are selected so that
C.sub.11=0 and C.sub.02=C.sub.20cos.sup.2.theta. can be satisfied,
the off-axial reflecting surface can be paraxially handled
similarly to the coaxial rotationally symmetrical optical
system.
[0203] An off-axial quadratic reflecting surface, such as that
shown in FIG. 36, at which the reference axis passes through two
focuses, generally satisfies the aforesaid relation. This fact can
readily be confirmed by obtaining the curvature at the surface
vertex of the optical system shown in FIG. 36, or because, if a
general formula of the off-axial quadratic reflecting surface at
which the reference axis passes through two focuses is expanded
into power series in the form of Equation 1 and the coefficients
are compared with each other, the following results can be
obtained:
C.sub.02=(1/a+1/b)cos .theta./4,
C.sub.20=(1/a+1/b) (4cos.theta.),
C.sub.11=0.
[0204] In FIG. 36, letting a and b be the distances between the two
focuses and the surface vertex, it is intuitively understood that
the power of the reflecting surface is 1/a+1/b. This fact can also
be confirmed by a calculation using Equation 10.
[0205] Incidentally, if a general spherical-surface formula is
expanded into power series, the coefficient of the second-degree
term is expressed as 1/(2R) (R: radius of curvature). Accordingly,
in the coordinate system of Equation 1, letting R.sub.x be the
radius of curvature of a paraxial region in the X, Z plane and
letting R.sub.y be the radius of curvature of the paraxial region
in the Y, Z plane, the following expressions are obtained:
C.sub.20=1/(2R.sub.x), C.sub.02=1(2R.sub.y).
[0206] Therefore, from Equation 27, if the following relation is
satisfied:
(R.sub.x/R.sub.y).multidot.(1/cos.sup.2q)=1, (Equation 28)
[0207] the focal lengths at all azimuths at a decentered reflecting
surface becomes coincident with each other.
[0208] b) Off-axial refracting surface
[0209] The off-axial refracting surface is not so simple as the
off-axial reflecting surface. This is because the diagonal elements
A and D of the Gaussian brackets are not "1" (a reciprocal relation
of A=1/D.noteq.1). However, this can be understood if a refracting
surface is regarded as a plane surface. If an optical system
includes a plane refracting surface, the optical system has an
angular magnification having azimuth dependence owing to the prism
effect of the plane refracting surface, and the angular
magnification is in general represented as D of the Gaussian
brackets. If this fact is borne in mind, it can be understood that
each component of the Gaussian brackets of a general off-axial
reflecting surface is represented by a term in which a prism effect
due to off-axial refraction is combined with a variation in power
due to a curved surface.
[0210] 6. Application to design
[0211] The paraxial theory of the off-axial optical system
constructed in the above-described manner and the paraxial tracing
method can be applied to the design of off-axial optical systems.
In the case of isotropic image formation whose magnification
generally does not depend on the azimuth, all paraxial quantities
are considered to be free of azimuth dependence over the entire
optical system. Accordingly, designing may be carried out in the
following procedure.
[0212] i) An optical system is arranged along a bent reference axis
so as to take account of the interference of an optical path and
the like.
[0213] ii) Then, the method of Gaussian brackets is used to perform
paraxial tracing for each azimuth, thereby determining the
curvature of each surface so that the paraxial quantities and the
image-plane positions of the entire optical system do not have
azimuth dependence.
[0214] Such designing method which is based on the azimuth
dependence of a paraxial quantity is an idea which has never been
thought of and which can offer extremely useful suggestions to the
designing of the off-axial optical system.
[0215] The above description has been made in connection with the
paraxial theory for the off-axial optical system and the method of
designing the skeleton of an optical system on the basis of the
paraxial theory.
[0216] Embodiments and numerical examples of the present invention
will be described below by using the definitions of the paraxial
theory of the off-axial optical system.
[0217] FIG. 1 is a view of the optical arrangement of a first
embodiment of the variable magnification optical system according
to the present invention. The optical arrangement shown in FIG. 1
includes a stop 11 and a first optical unit (a first moving optical
unit) 12 which serves as an objective system for forming an object
image, and an intermediate image forming plane 13 is formed by the
first optical unit 12. The shown optical arrangement also includes
a second optical unit (a fixed optical unit) 14 and a third optical
unit (a second moving optical unit) 15, and a combined system 17
consisting of the second optical unit 14 and the third optical unit
15 serves as a relay optical system for again forming the image of
the intermediate image forming plane 13 on a final image forming
plane 16. The entire arrangement is such that the first optical
unit 12 of the front stop type is followed by the relay optical
system 17. Incidentally, in FIG. 1, each of the optical units is
diagrammatically shown.
[0218] In FIG. 1, a dot-dashed line represents a principal ray
passing through the center of the angle of view. The principal ray
passes through the optical units while being repeatedly reflected
by off-axial reflecting surfaces (not shown) in each of the optical
units, and reaches the final image forming plane 16. As is apparent
from the above description, the variable magnification optical
system according to the present invention is an off-axial
reflecting optical system in which an optical axis similar to that
of the coaxial optical system does not definitely exist.
[0219] For this reason, as described previously, a ray which passes
from the center of an object plane through the center of the stop
11 of the variable magnification optical system and reaches the
center of the final image forming plane 16 is determined as a
reference axis ray, and the reference axis ray is defined as a
reference axis. In other words, in FIG. 1, the dot-dashed line
corresponds to the reference axis ray.
[0220] Each of the first optical unit 12, the second optical unit
14 and the third optical unit 15 is composed of two refracting
surfaces and a plurality of curved reflecting surfaces which are
inclined with respect to the reference axis. The third optical unit
15 has an entering reference axis and an exiting reference axis
which differ from each other by 180.degree. in direction.
[0221] In the arrangement of FIG. 1, if the stop 11 and the second
optical unit 14 are fixed and the first optical unit 12 and the
third optical unit 15 are made appropriately movable in the
directions of the corresponding arrows shown in FIG. 1, a variable
magnification optical system with the final image forming plane 16
fixed can be realized. Incidentally, the respective arrows indicate
the directions in which the first optical unit 12 and the third
optical unit 15 move from a wide-angle end toward a telephoto
end.
[0222] In the first embodiment, since an optical element having an
entering reference axis and an exiting reference axis which differ
from each other by 180.degree. in direction is introduced as the
third optical unit 15, the final image forming plane 16 can be
fixed, although the optical path length from a reference point on
the object side of the variable magnification optical system to the
final image forming plane 16 varies during the variation of the
magnification of the variable magnification optical system.
[0223] In the variable magnification optical system according to
the present invention, the second optical unit 14 disposed in front
of the relay optical system 17 is made to function as an optical
unit which exhibits a largest variation in lateral magnification
during the variation of the magnification, i.e., an optical unit
whose ratio of (the lateral magnification at the telephoto end) to
(the lateral magnification at the wide-angle end) is largest, i.e.,
a variator having a so-called magnification varying action.
[0224] If the lateral magnification of the second optical unit 14
is to be varied, the distance between the intermediate image
forming plane 13 which is the object point of the second optical
unit 14 and the second optical unit 14 may be varied. In the
variable magnification optical system of the first embodiment, the
magnification varying action is obtained by relatively moving the
intermediate image forming plane 13 with respect to the second
optical unit 14 by moving the first optical unit 12 with the second
optical unit 14 fixed. During the variation of the magnification,
the first optical unit 12 moves toward the second optical unit 14
from the wide-angle end toward the telephoto end so that the
distance between the intermediate image forming plane 13 and the
second optical unit 14 is reduced. The movement of the final image
forming plane 16 which results from the magnification varying
action is controlled by moving the third optical unit 15 away from
the second optical unit 14.
[0225] The variation of the optical path length during this time
will be described below. FIG. 2 is an explanatory view showing the
first embodiment in the form of a coaxial system. As shown in FIG.
2, the variable magnification optical system of the first
embodiment is arranged in such a manner that the stop 11 and the
first optical unit 12 are fixed, while the first optical unit 12
and the third optical unit 15 are movable.
[0226] If the distance between the second optical unit 14 and the
third optical unit 15 which constitute the relay optical system 17
is varied to vary the focal length of the relay optical system 17
and hence the image forming magnification, then the magnification
variation ratio of the entire variable magnification optical system
of FIG. 2 is determined by the magnification variation ratio of the
relay optical system 17 relative to the object-side angle of view
of the first optical unit 12.
[0227] In the case of a coaxial refracting optical system, if an
image forming plane is to be fixed during the variation of its
magnification, it is general practice to make constant the optical
path length from the object-side reference point of the optical
system (for example, the stop 11 in FIG. 11) to the image forming
plane. In contrast, in the variable magnification optical system
according to the present invention, since the optical element
having the entering reference axis and the exiting reference axis
which differ from each other by 180.degree. in direction is
employed as the third optical unit 15, the optical path length from
the object-side reference point of the optical system to the final
image plane, i.e., the final image forming plane 16 moves, during
the variation of the magnification, as represented by FIG. 2.
However, the optical arrangement of the first embodiment of FIG. 1
is such that the final image forming plane 16 is physically fixed.
This optical arrangement will be described below.
[0228] When the focal length of the first embodiment is set to the
wide-angle end, the entire optical path length varies as shown by
distances e.sub.0W, e.sub.1W, e.sub.2W and e.sub.3W. The distance
e.sub.0W is the distance from the stop 11 to the front principal
point of the first optical unit 12, the distance e.sub.1W is the
distance from the rear principal point of the first optical unit 12
to the front principal point of the second optical unit 14, the
distance e.sub.2W is the distance from the rear principal point of
the second optical unit 14 to the front principal point of the
third optical unit 15, and the distance e.sub.3W is the distance
from the rear principal point of the third optical unit 15 to the
final image forming plane 16. Similarly, when the focal length is
set to the telephoto end, the entire optical path length varies as
shown by distances e.sub.0T, e.sub.1T, e.sub.2T and e.sub.3T.
Symbols d1 and d3 denote the respective amounts of movements of the
first optical unit 12 and the third optical unit 15 during the
variation of the magnification. The variation of the entire optical
path length during the variation of the magnification is calculated
in the following manner.
[0229] According to the optical arrangement shown FIG. 1, the
respective distances e.sub.0T, e.sub.1T, e.sub.2T and e.sub.3T for
the telephoto end are expressed by the following equations: 7 e 0 T
= e 0 W + d1 , e 1 T = e 1 W - d1 , e 2 T = e 2 W + d3 , e 3 T = e
3 W + d3 . ] ( 1 )
[0230] Specifically, as the focal length of the first embodiment is
varied from the wide-angle end toward the telephoto end, the
optical path length between the stop 11 and the first optical unit
12 becomes longer, the optical path length between the first
optical unit 12 and the second optical unit 14 becomes shorter, the
optical path length between the second optical unit 14 and the
third optical unit 15 becomes longer, and the optical path length
between the third optical unit 15 and the image plane 16 becomes
longer.
[0231] When the focal length is at the telephoto end, the entire
optical path length L.sub.T is:
L.sub.T=e.sub.0T+e.sub.1T+e.sub.e.sub.2T+e.sub.3T.
[0232] By substituting this L.sub.T for Equation (1), from
L.sub.W=e.sub.0W+e.sub.1W+e.sub.2W+e.sub.3W,
[0233] the relation expressed by the following equation is
obtained:
L.sub.T=L.sub.W+2d3. (2)
[0234] Accordingly, in the first embodiment, although the final
image forming plane 16 is fixed, as the focal length is varied from
the wide-angle end toward the telephoto end, the entire optical
path length becomes longer by 2d3.
[0235] In the first embodiment, since the second optical unit 14
which serves as the variator is a fixed optical unit and the
magnification is varied by moving the first optical unit 12
disposed in front of the second optical unit 14, it is possible to
obtain the effect of increasing the distance from the image plane
on the telephoto side to an exit pupil. This effect will be
described below with reference to FIGS. 3(A) and 3(B) which are
explanatory views of an exit pupil distance.
[0236] The arrangement shown in FIGS. 3(A) and 3(B) is identical to
that shown in FIG. 2, but the ray shown in FIGS. 3(A) and 3(B) is
an off-axial principal ray which passes through the center of the
stop 11. In FIGS. 3(A) and 3(B), the respective intersections of
the off-axial principal ray and the optical axis shown by a
dot-dashed line are pupils P.sub.W and P.sub.T conjugate to the
stop 11. The respective exit pupils lie at positions where the
virtual images of the pupils P.sub.W and P.sub.T are formed by the
third optical unit 15. In FIGS. 3(A) and 3(B), symbols EP.sub.W and
EP.sub.T denote the exit pupil distances from the image plane to
the respective exit pupils.
[0237] Referring to FIG. 3(B), since the image forming
magnification of the first optical unit 12 is greater than 1 (the
stop 11 is located immediately before the first optical unit 12), a
position at which an image of the stop 11 is formed by the first
optical unit 12 is displaced toward the first optical unit 12 by an
amount not less than the amount of movement of the first optical
unit 12. Accordingly, the position of the pupil P.sub.T moves
closer to the object side than the pupil P.sub.W.
[0238] The pupil P.sub.T at the telephoto end is more distant from
the third optical unit 15 than the pupil P.sub.W at the wide-angle
end, and the distance from the third optical unit 15 to the final
image forming plane 16 is also longer at the telephoto end than at
the wide-angle end, so that an exit pupil distance EP.sub.T at the
telephoto end becomes longer than an exit pupil distance EP.sub.W
at the wide-angle end. Accordingly, by appropriately setting the
position of the exit pupil at the wide-angle end, it is possible to
increase the exit pupil distance over the entire range of variation
of magnification.
[0239] Accordingly, the first embodiment has the advantage that its
optical arrangement can be made closer to a telecentric state by
increasing the distance from the image plane to the exit pupil on
the telephoto side. Accordingly, if an object image is formed on a
solid-state image pickup device such as a CCD by using the first
embodiment, it is possible to prevent occurrence of shading over
the entire range of variation magnification, so that the quality of
an image to be picked up can be improved.
[0240] In the first embodiment, the stop 11 is disposed on the
object side of the first optical unit 12 and reflecting surfaces
are used in the first optical unit 12 so as to collect a light
beam, so that the first optical unit 12 which serves as an
objective optical system can be made a thin optical system in spite
of its wide angle of view. Although FIGS. 1 and 2 show that the
light beam from the object forms one intermediate image before
reaching the final image forming plane 16, the light beam actually
forms at least one more intermediate image between the intermediate
image forming plane 13 and the final image forming plane 16,
thereby relaying an image. This construction prevents not only an
increase in the thickness of the first optical unit 12 but also
increases in the thicknesses of the second optical unit 14 and the
third optical unit 15 which follow the intermediate image forming
plane 13. Incidentally, the "thickness of an optical system"
referred to herein means the thickness taken in a direction
perpendicular to the surface of the sheet of FIG. 1, and the term
"thin" or similar expressions used herein mean that such thickness
is small.
[0241] In the first embodiment, the third optical unit 15 is
arranged so that the entering reference axis and the exiting
reference axis differ from each other by 180.degree. in direction.
This arrangement reduces the overall length in a horizontal
direction parallel to the sheet surface of FIG. 1.
[0242] The variable magnification optical system according to the
present invention has decentered reflecting surfaces and,
therefore, suffer various decentering aberrations. To correct these
decentering aberrations over the entire range of variation of
magnification, it is necessary to correct the decentering
aberrations in the respective optical units or to make the
decentering aberrations cancel one another among the optical units.
Although the object point of the third optical unit 15 of the first
embodiment moves during a magnification varying operation, it is
generally difficult to correct a decentering aberration in the
corresponding optical unit itself irrespective of the movement of
the object point. For this reason, the third optical unit 15 (a
moving optical unit B) of the variable magnification optical system
according to the present invention has curved reflecting surfaces
having cross-sectional shapes which are asymmetrical, for example,
in a plane containing the reference axis and are inclined with
respect to the reference axis, so that the decentering aberration
is corrected as fully as possible in the third optical unit 15 with
respect to a particular object point. In addition, decentering
aberration variations due to the movement of the object point are
made to cancel one another among the optical units. Thus, the
variable magnification optical system is capable of correcting the
decentering aberrations over the entire range of variation of
magnification.
[0243] FIG. 4 is a view of the optical arrangement of a second
embodiment of the variable magnification optical system according
to the present invention. The second embodiment has an arrangement
in which, in addition to the arrangement of the first embodiment, a
first optical unit consisting of a negative lens 61 is disposed in
front of the stop 11 and a block 65 having the shape of a plane
parallel plate is disposed in front of the final image forming
plane 16.
[0244] In FIG. 4, optical units 62, 63 and 64 respectively
correspond to the first optical unit 12, the second optical unit 14
and the third optical unit 15 of the first embodiment. Since the
block 65 does not have a refractive power, the second embodiment is
a variable magnification optical system which is basically composed
of four optical units, and as its focal length is varied from the
wide-angle end to the telephoto end, the second optical unit 62 and
the fourth optical unit 64 move in the directions of the
corresponding arrows. The first optical unit 61 and the third
optical unit 63 are fixed optical units.
[0245] By adding the negative lens 61 to the first embodiment in
this manner, it is possible to effectively correct chromatic
aberrations which occur at the refracting surfaces of the second
optical unit 62, the third optical unit 63 and the fourth optical
unit 64.
[0246] In addition, in the second embodiment, if an optical system
having a lateral magnification whose absolute value is greater than
"1" is disposed between the fourth optical unit 64 and the block
65, it is possible to achieve the effect of reducing the amounts of
movements of the second optical unit 62 and the fourth optical unit
64 both of which are moving optical units.
[0247] FIG. 5 is a view of the optical arrangement of a third
embodiment of the variable magnification optical system according
to the present invention. The third embodiment differs from the
first embodiment in that the second optical unit 14 is replaced
with an optical unit having an entering reference axis and an
exiting reference axis which differ from each other by 180.degree.
in direction. In the optical arrangement shown in FIG. 5, if the
focal length is to be from the wide-angle end toward the telephoto
end, the first optical unit 12 and the third optical unit 15 are
moved in the directions of the corresponding arrows with the stop
11 and the second optical unit 14 fixed. During the variation of
the magnification, the final image forming plane 16 is fixed.
[0248] The coaxial system of the third embodiment is shown in FIG.
2, and the first embodiment and the third embodiment are basically
identical to each other.
[0249] However, with the arrangement of the third embodiment, it is
possible to reduce the size of the optical arrangement to a further
extent in the direction in which the reference axis ray from an
object enters.
[0250] Incidentally, if the second optical unit 14 which serves as
the variator is replaced with the optical element having the
entering reference axis and the exiting reference axis which differ
from each other by 180.degree. in direction, as in the case of the
third embodiment, the amount of movement of the third optical unit
15 can be made smaller by the arrangement of the third embodiment
in which the first optical unit 12 is moved with the second optical
unit 14 fixed, than by an arrangement in which the second optical
unit 14 is moved with the first optical unit 12 fixed. This is
because, in the optical arrangement of FIG. 5, when the focal
length is to be varied the wide-angle end toward the telephoto end,
the third optical unit 15 must be moved away from the second
optical unit 14, but if the second optical unit 14 is moved toward
the first optical unit 12, the second optical unit 14 moves toward
the third optical unit 15 as well, so that the third optical unit
15 must be moved by an amount equivalent to the amount of movement
of the second optical unit 14. With the arrangement of the third
embodiment, it is possible to reduce the amount of movement of the
third optical unit 15 and hence the required volume to be occupied
by the variable magnification optical system, whereby the entire
apparatus can be miniaturized to a further extent.
[0251] In the third embodiment as well, if a fixed negative lens is
provided on the object side of the stop 11, it is possible to
effectively correct chromatic aberration.
[0252] FIG. 6 is a view of the optical arrangement of a fourth
embodiment of the variable magnification optical system according
to the present invention. The fourth embodiment differs from the
third embodiment in that the first optical unit 12 is replaced with
an optical unit having an entering reference axis and an exiting
reference axis which differ from each other by 180.degree. in
direction. Similarly to each of the first and third embodiments,
the fourth embodiment is composed of the first optical unit 12, the
second optical unit 14 and the third optical unit 15, and each of
the optical units 12, 14 and 15 is composed of two refracting
surfaces and a plurality of curved reflecting surfaces which are
inclined with respect to the reference axis.
[0253] In the fourth embodiment, each of the three optical units
has an entering reference axis and an exiting reference axis which
differ from each other by 180.degree. in direction. The optical
units 12, 14 and 15 are diagrammatically shown in FIG. 6 (in which
none of their reflecting surfaces is shown).
[0254] In the fourth embodiment of the variable magnification
optical system, as the focal length is varied from the wide-angle
end toward the telephoto end, the first optical unit 12 and the
third optical unit 15 are moved in the directions of the
corresponding arrows with the stop 11 and the second optical unit
14 fixed, while the entire optical path length is being varied with
the final image forming plane 16 fixed.
[0255] The variation of the entire optical path length during the
variation of the magnification is calculated in the following
manner, by using the distances e.sub.0W, e.sub.1W, e.sub.2W and
e.sub.3W for the wide-angle end, the distances e.sub.0T, e.sub.1T,
e.sub.2T and e.sub.3T for the telephoto end, and the amounts of
movements, d1 and d3, of the respective optical units 12 and 15
relative to the wide-angle end.
[0256] FIG. 7 is an explanatory view showing the fourth embodiment
in the form of a coaxial system. According to the optical
arrangement shown in FIG. 6, the respective distances e.sub.0T,
e.sub.1T, e.sub.2T and e.sub.3T for the telephoto end are expressed
by the following equations: 8 e 0 T = e 0 W - d1 , e 1 T = e 1 W -
d1 , e 2 T = e 2 W + d3 , e 3 T = e 3 W + d3 . ] ( 3 )
[0257] Specifically, as the focal length of the fourth embodiment
is varied from the wide-angle end toward the telephoto end, the
optical path length between the stop 11 and the first optical unit
12 becomes shorter, the optical path length between the first
optical unit 12 and the second optical unit 14 becomes shorter, the
optical path length between the second optical unit 14 and the
third optical unit 15 becomes longer, and the optical path length
between the third optical unit 15 and the image plane 16 becomes
longer.
[0258] When the focal length is at the telephoto end, the entire
optical path length L.sub.T is:
L.sub.T=e.sub.0T+e.sub.1T+e.sub.2T+e.sub.3T.
[0259] By substituting this L.sub.T for Equation (3), from
L.sub.W=e.sub.0W+e.sub.1W+e.sub.2W+e.sub.3W,
[0260] the relation expressed by the following equation is
obtained:
L.sub.T=L.sub.W-2d1+2d3. (4)
[0261] Since the amount of movement, d1, of the first optical unit
12 and the amount of movement, d3, of the third optical unit 15 in
general differ from each other, the entire optical path length in
the fourth embodiment varies by (-2d1+2d3) as the focal length is
varied from the wide-angle end toward the telephoto end.
[0262] In the fourth embodiment, the second optical unit 14 and the
final image forming plane 16 are fixed, whereas two optical units,
i.e., the first optical unit 12 and the third optical unit 15, are
physically movable. However, each of the first optical unit 12 and
the third optical unit 15 has the entering reference axis and the
exiting reference axis which differ from each other by 180.degree.
in direction, so that three optical units are movable as viewed
from the coaxial system shown in FIG. 7 and the entire optical path
length can be varied with the image plane actually fixed.
[0263] FIG. 8 shows a coaxial system in which the second optical
unit 14 of the arrangement of FIG. 7 is fixed. FIG. 8 differs from
FIG. 7 in that the coaxial system for the telephoto end is shown at
a position shifted toward the right by 2d1 as a whole. It can be
seen from this illustration that the basic arrangement of the
fourth embodiment is identical to that of the first embodiment
shown in FIG. 2, except for the position of the stop 11.
[0264] Incidentally, in the fourth embodiment as well, the second
optical unit 14 which serves as the variator is replaced with the
optical element having the entering reference axis and the exiting
reference axis which differ from each other by 180.degree. in
direction, as in the case of the third embodiment, so that it is
possible to reduce the amount of movement of the third optical unit
15 and hence the required volume to be occupied by the variable
magnification optical system, whereby the entire apparatus can be
miniaturized to a further extent.
[0265] In each of the first to fourth embodiments, the stop 11 is
disposed on the object side of the first optical unit 12 and the
reflecting surfaces are used in the first optical unit 12 so as to
collect a light beam, so that the first optical unit 12 which
serves as an objective optical system can be realized as a thin
optical system in spite of its wide angle of view.
[0266] In addition, each of the second optical unit 14 and the
third optical unit 15 is composed of curved reflecting surfaces
which are inclined with respect to the reference axis, so that the
intermediate image formed by the first optical unit 12 is relayed
by a compact arrangement. Specifically, each of the first to fourth
embodiments is arranged to relay an image not only through the
intermediate image forming plane 13 of the first optical unit 12
but also by forming intermediate images in some of the optical
units.
[0267] FIG. 9 is a view showing an example of the construction of
one of the optical units used in each of the above-described
embodiments. An optical element B1 is formed as a transparent body
on which two refracting surfaces and a plurality of internal
reflecting surfaces are formed, the plurality of internal
reflecting surfaces being inclined with respect to a reference
axis. The optical element B1 includes a refracting surface 71 lying
on an entrance side, curved reflecting surfaces 72, 73, 74, 75 and
76, and a refracting surface 77 lying on an exit side. Each of the
reflecting surfaces 72, 73, 74, 75 and 76 is an internal reflecting
surface coated with an evaporated reflecting film.
[0268] If one optical unit is integrally constructed in the
above-described manner, the positional accuracy of each surface
becomes high compared to an arrangement in which individual
surfaces are independently arranged, so that adjustment of the
positions, inclinations or the like of the respective surfaces can
be omitted.
[0269] In addition, since members for supporting the reflecting
surfaces are not needed, the required number of constituent
components is reduced.
[0270] In FIG. 9, the reference axis is represented by a dot-dashed
line, and the entering reference axis enters the optical element B1
through the refracting surface 71, while the exiting reference axis
exits from the optical element B1 through the refracting surface
77. The entering and exiting reference axes are parallel to each
other and their directions are 180.degree. differ from each other.
Accordingly, if the optical element B1 is made to move parallel to
the entering and exiting reference axes, the amount of movement of
the optical element B1 and the optical path length thereof can be
increased or decreased with respect to either of the optical units
anterior and posterior to the optical element B1.
[0271] In addition, holes or the like each of which receives a
guide bar for guiding the magnification varying movement of an
optical unit may be formed in predetermined transparent bodies of
the type shown in FIG. 9 in the manner shown in FIG. 10. With this
arrangement, since the variable magnification optical system can be
composed of such transparent bodies alone, a member such as a
barrel for holding normal lenses is not needed, so that the
required number of constituent components can be reduced to a
further extent.
[0272] FIG. 11 is a view showing another example of the
construction of the optical unit. The optical element B1 is formed
as a transparent body on which two refracting surfaces and a
plurality of internal reflecting surfaces are formed, the plurality
of internal reflecting surfaces being inclined with respect to a
reference axis. The optical element B1 includes a refracting
surface 81 lying on an entrance side, curved reflecting surfaces
82, 83, 84 and 85, and a refracting surface 86 lying on an exit
side. Each of the reflecting surfaces 82, 83, 84 and 85 is an
internal reflecting surface coated with an evaporated reflecting
film.
[0273] The optical element B1 shown in FIG. 11 differs from the
example shown in FIG. 9 in that the entering and exiting reference
axes are parallel to each other and their directions coincide with
each other. Accordingly, as in the case of normal lenses, if the
optical element B1 shown in FIG. 11 is made to move parallel to the
entering and exiting reference axes, the optical path length
between the optical element B1 and either one of the optical units
anterior and posterior to the optical element B1 is increased by
the amount of movement of the optical element B1, whereas the
optical path length between the optical element B1 and the other
optical unit is decreased by the same amount of movement.
[0274] The variable magnification optical system according to the
present invention is formed as a thin variable magnification
optical system by appropriately using the aforesaid type of optical
element for each of the optical units. Specifically, each of the
optical elements B1 shown in FIGS. 9 and 11 is realized as a thin
optical element having a construction in which an intermediate
image is formed in its inside and concave reflecting surfaces are
actively employed to relay an image in a compact body while
preventing divergence of a light beam.
[0275] Accordingly, the variable magnification optical system
according to the present invention includes not only the
intermediate image forming plane 13 formed by the first optical
unit 12 but also another intermediate image forming plane formed in
a particular one of the optical units each of which is composed of
an optical element such as that shown in FIG. 9 or 11.
Incidentally, if such an optical element is employed as the first
optical unit, the first intermediate image forming plane numbered
from the object plane is present in the first optical unit.
[0276] The variable magnification optical system according to the
present invention is not limited to the arrangement of any of the
above-described embodiments. For example, as described previously
in connection with the second embodiment, a single lens, a lens
system or the like may also be added.
[0277] Prior to the detailed description of individual numerical
examples, reference will be made to terms which are herein used to
express various constituent elements of the numerical examples, and
matters common to all the numerical examples.
[0278] FIG. 12 is an explanatory view of a coordinate system which
defines the constituent data of an optical system according to the
present invention. In each of the numerical examples of the present
invention, the i-th surface is a surface which lies at the i-th
position numbered from an object side from which a ray travels
toward an image plane (the ray is shown by dot-dashed lines in FIG.
12 and is hereinafter referred to as the reference axis ray).
[0279] In FIG. 12, a first surface R1 is a stop, a second surface
R2 is a refracting surface coaxial with the first surface R1, a
third surface R3 is a reflecting surface which is tilted with
respect to the second surface R2, a fourth surface R4 is a
reflecting surface which is shifted and tilted with respect to the
third surface R3, a fifth surface R5 is a reflecting surface which
is shifted and tilted with respect to the fourth surface R4, and a
sixth surface R6 is a refracting surface which is shifted and
tilted with respect to the fifth surface R5. All of the second
surface R2 to the sixth surface R6 are arranged on one optical
element composed of a medium such as glass or plastics. In FIG. 12,
such optical element is shown as a first optical element B1.
[0280] Accordingly, in the arrangement shown in FIG. 12, the medium
between an object plane (not shown) and the second surface R2 is
air, the second surface R2 to the sixth surface R6 are arranged on
a certain common medium, and the medium between the sixth surface
R6 and a seventh surface R7 (not shown) is air.
[0281] Since the optical system according to the present invention
is an off-axial optical system, the surfaces which constitute part
of the optical system do not have a common optical axis. For this
reason, in each of the numerical examples of the present invention,
an absolute coordinate system is set, the origin of which is the
central point of an effective ray diameter at the first surface
which is the stop. In the present invention, each axis of the
absolute coordinate system is defined as follows:
[0282] Z axis: reference axis which passes through the origin and
extends to the second surface R2;
[0283] Y axis: straight line which passes through the origin and
makes an angle of 90.degree. with the z axis in the
counterclockwise direction in a tilting plane (on the surface of
the sheet of FIG. 12); and
[0284] X axis: straight line which passes through the origin and is
perpendicular to each of the Z and Y axes (perpendicular to the
surface of the sheet of FIG. 12).
[0285] If the surface shape of the i-th surface which constitutes
part of the optical system is to be expressed, it is possible to
more readily understand and recognize such surface shape by setting
a local coordinate system the origin of which is a point at which
the reference axis intersects with the i-th surface, and expressing
the surface shape of the i-th surface by using the local coordinate
system than by expressing the surface shape of the i-th surface by
using the absolute coordinate system. Accordingly, in some
numerical examples of the present invention the constituent data of
which are shown herein, the surface shape of the i-th surface is
expressed by its local coordinate system.
[0286] The tilting angle of the i-th surface in the Y, Z plane is
expressed by an angle .theta.i (unit: degree) which shows a
positive value in the counterclockwise direction with respect to
the Z axis of the absolute coordinate system. Accordingly, in each
of the numerical examples of the present invention, the origins of
the local coordinate systems of the respective surfaces are located
on the Y, Z plane, as shown in FIG. 12. The tilting or shifting of
the surfaces is absent in the X-Z plane or the X-Y plane. In
addition, the y and z axes of the local coordinates (x, y, z) of
the i-th surface are inclined by the angle .theta.i in the Y, Z
plane with respect to the absolute coordinate system (X, Y, Z).
Specifically, the x, y and z axes of the local coordinates (x, y,
z) are set in the follow manner:
[0287] z axis: straight line which passes through the origin of the
local coordinates and makes the angle .theta.i with the Z direction
of the absolute coordinate system in the counterclockwise direction
in the Y, Z plane;
[0288] y axis: straight line which passes through the origin of the
local coordinates and makes an angle of 90.degree. with the z
direction of the local coordinates in the counterclockwise
direction in the Y, Z plane; and
[0289] x axis: straight line which passes through the origin of the
local coordinates and is perpendicular to the Y, Z plane.
[0290] Symbol Di indicates a scalar which represents the distance
between the origin of the local coordinates of the i-th surface and
that of the (i+1)-st surface. Symbols Ndi and .upsilon.di
respectively indicate the refractive index and the Abbe number of
the medium between the i-th surface and the (i+1)-st surface. In
FIG. 12, each of the stop and the final image forming plane is
shown as one plane surface.
[0291] The optical system of each of the numerical examples of the
present invention varies its entire focal length (magnification) by
the movement of a plurality of optical elements. Regarding each of
the numerical examples which have the numerical data shown herein,
the cross section of its optical system and the numerical data are
shown with respect to three positions, i.e., a wide-angle end (W),
a telephoto end (T) and a middle position (M).
[0292] If the optical element shown in FIG. 12 moves in the Y, Z
plane, the origin (Yi, Zi) of each of the local coordinate systems
which represent the positions of the respective surfaces takes on a
different value for each varied magnification position. However, in
the case of the numerical examples shown herein, since the optical
element is assumed to move in only the Z direction for the purpose
of variation of magnification, the coordinate value Zi is expressed
by Zi(W), Zi(M) and Zi(T) in the order of the wide-angle end, the
middle position and the telephoto end which respectively correspond
to three states to be taken by the optical system.
[0293] Incidentally, the coordinate values of each of the surfaces
represent those obtained at the wide-angle end, and each of the
middle position and the telephoto end is expressed as a difference
between the coordinate values obtained at the wide-angle end and
the coordinate values obtained at the respective one of the middle
position and the telephoto end. Specifically, letting "a" and "b"
be the respective amounts of movements of the optical element at
the middle position (M) and the telephoto end (T) with respect to
the wide-angle end (W), these amounts of movements are expressed by
the following equations:
Zi(M)=i(W)+a,
Zi(T)=Zi(W)+b.
[0294] If all the surfaces move in their z plus directions, the
signs of "a" and "b" are positive, whereas if they move in their Z
minus directions, the signs of "a" and "b" are negative. The
surface-to-surface distance Di which varies with these movements is
a variable, and the values of the variable at the respective varied
magnification positions are collectively shown on tables which will
be referred to later.
[0295] Each of the numerical examples of the present invention has
spheric surfaces and aspheric surfaces of rotational asymmetry.
Each of the spheric surfaces has a spherical shape expressed by a
radius of curvature R.sub.i. The sign of the radius of curvature
R.sub.i is plus if the center of curvature is located in the z-axis
plus direction of the local coordinates, whereas if the center of
curvature is located in the z-axis minus direction of the local
coordinates, the sign of the radius of curvature R.sub.i is
minus.
[0296] Each of the spheric surfaces is a shape expressed by the
following equation: 9 0 z = ( x 2 + y 2 ) / R i 1 + { 1 - ( x 2 + y
2 ) / R i 2 } 1 / 2 .
[0297] In addition, the optical system according to the present
invention has at least one aspheric surface of rotational
asymmetry, and its shape is expressed by the following equation in
which all the terms that contain the variable x having an odd
exponent are omitted from Equation 1 and such binomial coefficient
is put in the coefficient term of each of the remaining terms of
Equation 1:
z=C.sub.02y.sup.2+C.sub.20x.sup.2+C.sub.03y.sup.3+C.sub.21x.sup.2y+C.sub.0-
4y.sup.4+C.sub.22x.sup.2y.sup.2+C.sub.40x.sup.4+C.sub.05y.sup.5+C.sub.23x.-
sup.2y.sup.3+C.sub.41x.sup.4y+C.sub.06y.sup.6+C.sub.24x.sup.2y.sup.4+C.sub-
.42x.sup.4y.sup.2+C.sub.60x.sup.6.
[0298] Since the above curved-surface equation has only
even-exponent terms regarding x, the curved surface expressed by
the above curved-surface equation has a shape symmetrical with
respect to the Y, Z plane. Further, if the following condition is
satisfied, a shape symmetrical with respect to the X-Z plane is
obtained:
C.sub.03=C.sub.21=C.sub.05=C.sub.23=C.sub.41=0.
[0299] Further, if the following equations are satisfied, a shape
of rotational symmetry is obtained:
C.sub.02=C.sub.20, C.sub.04=C.sub.40=C.sub.22/2,
C.sub.06=C.sub.60=C.sub.2- 4/3=C.sub.42/3.
[0300] If the above conditions are not satisfied, a shape of
rotational asymmetry is obtained.
[0301] A horizontal half-angle of view u.sub.X is the maximum angle
of view of a light beam incident on the first surface R1 in the Y,
Z plane of FIG. 12, while a vertical half-angle of view u.sub.X is
the maximum angle of view of a light beam incident on the first
surface R1 in the X, Z plane of FIG. 12.
[0302] The brightness of the optical system is represented by an
entrance pupil diameter which is the diameter of an entrance pupil.
The effective image area in the image plane is represented by an
image size. The image size is represented by a rectangular region
having a horizontal size taken in the y direction of the local
coordinate system and a vertical size taken in the x direction of
the local coordinate system.
[0303] Regarding the numerical examples which are illustrated
together with the constituent data, their respective lateral
aberration charts are shown. Each of the lateral aberration charts
shows the lateral aberrations of a light beam for the wide-angle
end (W), the middle position (M) and the telephoto end (T), and the
lateral aberrations are those of the light beam which is incident
on the stop R1 at an angle of incidence which is defined by a
horizontal angle of incidence and a vertical angle of incidence
which are (u.sub.Y, u.sub.X), (0, u.sub.X), (-u.sub.Y, u.sub.X),
(u.sub.Y, 0), (0, 0) and (-u.sub.Y, 0), respectively. In each of
the lateral aberration charts, the horizontal axis represents the
height of incidence on the pupil, and the vertical axis represents
the amount of aberration. In any of the numerical examples, since
each of the surfaces basically has a shape symmetrical with respect
to the Y, Z plane, the plus and minus directions of a vertical
angle of view are the same in the lateral aberration chart. For
this reason, the lateral aberration chart relative to the minus
direction is omitted for the sake of simplicity.
[0304] The numerical examples are described below.
[0305] [Numerical Example 1]
[0306] Numerical Example 1 is a variable magnification optical
system having a magnification variation ratio of approximately
2.8.times.. FIGS. 13, 14 and 15 are cross-sectional views taken in
the Y, Z plane, showing the respective optical paths of Numerical
Example 1 relative to the wide-angle end (W), the middle position
(M) and the telephoto end (T). Constituent data for Numerical
Example 1 are shown below.
1 WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END HORIZONTAL
HALF-ANGLE 27.3 19.0 9.8 OF VIEW VERTICAL HALF-ANGLE 21.2 14.5 7.4
OF VIEW APERTURE DIAMETER 1.30 1.40 2.00 i Yi Zi(W) .theta.i Di Ndi
.nu.di FIRST OPTICAL ELEMENT B1 (NEGATIVE LENS) 1 0.00 0.00 0.00
0.70 1.51633 64.15 2 0.00 0.70 0.00 1.33 1 3 0.00 2.03 0.00
VARIABLE STOP SECOND OPTICAL ELEMENT B2 4 0.00 3.03 0.00 6.00
1.49171 57.40 REFRACTING SURFACE 5 0.00 9.03 30.00 8.00 1.49171
57.40 REFLECTING SURFACE 6 -6.93 5.03 30.00 7.60 1.49171 57.40
REFLECTING SURFACE 7 -6.93 12.63 30.00 8.00 1.49171 57.40
REFLECTING SURFACE 8 -13.86 8.63 30.00 10.00 1.49171 57.40
REFLECTING SURFACE 9 -13.86 18.63 0.00 VARIABLE 1 REFRACTING
SURFACE THIRD OPTICAL ELEMENT B3 10 -13.86 22.04 0.00 6.00 1.49171
57.40 REFRACTING SURFACE 11 -13.86 28.04 -30.00 8.00 1.49171 57.40
REFLECTING SURFACE 12 -6.93 24.04 -30.00 7.60 1.49171 57.40
REFLECTING SURFACE 13 -6.93 31.64 -30.00 8.00 1.49171 57.40
REFLECTING SURFACE 14 0.00 27.64 -30.00 6.00 1.49171 57.40
REFLECTING SURFACE 15 0.00 33.64 0.00 VARIABLE 1 REFRACTING SURFACE
FOURTH OPTICAL ELEMENT B4 16 0.00 36.97 0.00 6.00 1.49171 57.40
REFRACTING SURFACE 17 0.00 42.97 30.00 8.00 1.49171 57.40
REFLECTING SURFACE 18 -6.93 38.97 15.00 8.00 1.49171 57.40
REFLECTING SURFACE 19 -10.93 45.90 0.00 8.00 1.49171 57.40
REFLECTING SURFACE 20 -14.93 38.97 -15.00 8.00 1.49171 57.40
REFLECTING SURFACE 21 -21.86 42.97 -30.00 6.00 1.49171 57.40
REFLECTING SURFACE 22 -21.86 36.97 0.00 VARIABLE 1 REFRACTING
SURFACE BLOCK B5 23 -21.86 35.86 0.00 2.08 1.51400 70.00 FILTER 24
-21.86 33.78 0.00 1.60 1.52000 74.00 FILTER 25 -21.86 32.18 0.00
1.00 1 26 -21.86 31.18 0.00 0.80 1.51633 64.15 COVER GLASS 27
-21.86 30.38 0.00 0.91 1 28 -21.86 29.47 -0.00 1 IMAGE PLANE
WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END D3 1.00 2.28 3.67 D9
3.41 2.12 0.73 D15 3.33 4.47 8.73 D22 1.11 2.25 6.51 R1-R3 Zi(M) =
Zi(W) Zi(T) = Zi(W) R4-R9 Zi(M) = Zi(W) + 1.28 Zi(T) = Zi(W) + 2.67
R10-R15 Zi(M) = Zi(W) Zi(T) = Zi(W) R16-R22 Zi(M) = Zi(W) + 1.14
Zi(T) = Zi(W) + 5.40 R23 Zi(M) = Zi(W) Zi(T) = Zi(W) SPHERICAL
SHAPE R1 R.sub.1 = .infin. R2 R.sub.2 = 10.000 R4 R.sub.4 = 10.000
R9 R.sub.9 = -11.861 R10 R.sub.10 = .infin. R15 R.sub.15 = 12.685
R16 R.sub.16 = -14.922 R22 R.sub.22 = .infin. R23 R.sub.23 =
.infin. R24 R.sub.24 = .infin. R25 R.sub.25 = .infin. R26 R.sub.26
= .infin. R27 R.sub.27 = .infin. ASPHERICAL SHAPE R5 C.sub.02 =
-1.65555e-02 C.sub.20 = -8.41274e-02 C.sub.03 = 6.41210e-04
C.sub.21 = 1.62616e-03 C.sub.04 = -1.02358e-04 C.sub.22 =
-5.23593e-04 C.sub.40 = -6.43577e-04 R6 C.sub.02 = 2.82163e-02
C.sub.20 = 4.34750e-02 C.sub.03 = -8.94216e-04 C.sub.21 =
4.23580e-03 C.sub.04 = 9.62013e-05 C.sub.22 = 3.79828e-04 C.sub.40
= -9.32251e-05 R7 C.sub.02 = -2.42076e-02 C.sub.20 = -2.27382e-02
C.sub.03 = -8.96687e-06 C.sub.21 = -3.94882e-03 C.sub.04 =
-1.22983e-04 C.sub.22 = 4.29189e-04 C.sub.40 = -2.34035e-06 R8
C.sub.02 = 4.99288e-02 C.sub.20 = 2.18880e-02 C.sub.03 =
-1.42024e-04 C.sub.21 = 1.03926e-04 C.sub.04 = 2.94885e-05 C.sub.22
= 1.05768e-04 C.sub.40 = -2.67713e-06 R11 C.sub.02 = -2.95501e-02
C.sub.20 = -4.64999e-02 C.sub.03 = -2.10262e-04 C.sub.21 =
-1.56787e-03 C.sub.04 = -1.77594e-05 C.sub.22 = -7.95819e-05
C.sub.40 = -1.28737e-04 R12 C.sub.02 = 1.08367e-02 C.sub.20 =
2.83473e-02 C.sub.03 = -2.31601e-05 C.sub.21 = 4.61247e-03 C.sub.04
= -1.00779e-04 C.sub.22 = 3.15656e-05 C.sub.40 = 1.27232e-03 R13
C.sub.02 = -2.00837e-03 C.sub.20 = 1.09453e-03 C.sub.03 =
3.22996e-04 C.sub.21 = 1.80481e-02 C.sub.04 = -3.43826e-04 C.sub.22
= -1.84712e-03 C.sub.40 = -2.12165e-03 R14 C.sub.02 = 3.49622e-02
C.sub.20 = 4.06364e-02 C.sub.03 = -2.73508e-04 C.sub.21 =
-4.35486e-04 C.sub.04 = 6.53193e-05 C.sub.22 = 7.60790e-05 C.sub.40
= 1.00004e-04 R17 C.sub.02 = -2.96485e-02 C.sub.20 = -1.49820e-02
C.sub.03 = -6.10223e-04 C.sub.21 = 1.73005e-03 C.sub.04 =
-1.42283e-05 C.sub.22 = -2.04680e-04 C.sub.40 = 2.11087e-04 R18
C.sub.02 = -1.30697e-02 C.sub.20 = 1.07759e-02 C.sub.03 =
-1.85268e-03 C.sub.21 = -4.38486e-04 C.sub.04 = -2.73769e-04
C.sub.22 = 5.82505e-04 C.sub.40 = 1.49662e-04 R19 C.sub.02 =
-2.46857e-02 C.sub.20 = -2.64590e-02 C.sub.03 = -2.12109e-04
C.sub.21 = 2.28021e-03 C.sub.04 = -3.40220e-05 C.sub.22 =
1.34011e-05 C.sub.40 = 3.64311e-05 R20 C.sub.02 = -1.16345e-02
C.sub.20 = -2.36411e-02 C.sub.03 = -3.60785e-04 C.sub.21 =
-1.68595e-03 C.sub.04 = -4.16485e-05 C.sub.22 = -2.72511e-04
C.sub.40 = -7.28477e-04 R21 C.sub.02 = -1.62057e-02 C.sub.20 =
-2.99524e-02 C.sub.03 = -3.74880e-04 C.sub.21 = 9.01456e-04
C.sub.04 = 2.18196e-06 C.sub.22 = -7.11991e-05 C.sub.40 =
2.44047e-05
[0307] The construction of Numerical Example 1 will be ed below.
The first optical element B1 is a negative which has the first
surface R1 and the second surface the third surface R3 is an
aperture plane. The optical element B2 is formed as one transparent
body on which the fourth surface R4 (entrance refracting surface),
the fifth to eighth surfaces R5 to R8 each of which is a decentered
curved internal reflecting surface, and the ninth surface R9 (exit
refracting surface) are formed. The third optical element B3 is
formed as one transparent body on which the tenth surface R10
(entrance refracting surface), the eleventh to fourteenth surfaces
R11 to R14 each of which is a decentered curved internal reflecting
surface, and the fifteenth surface R15 (exit refracting surface)
are formed. The fourth optical element B4 is formed as one
transparent body on which the sixteenth surface R16 (entrance
refracting surface), the seventeenth to twenty-first surfaces R17
to R21 each of which is a decentered curved internal reflecting
surface, and the twenty-second surface R22 (exit refracting
surface) are formed.
[0308] The twenty-third to twenty-seventh surfaces R23 to R27 are
those of plane parallel plates such as a filter and a cover glass.
The surfaces R23 to R27 constitute the block B5. The twenty-eighth
surface R28 is a final image plane in which the image pickup
surface of an image pickup device such as a CCD is positioned.
[0309] The optical elements of Numerical Example 1 are grouped into
four optical units which constitute a variable magnification
optical system. Specifically, the first optical element B1 and the
stop R3 constitute the first optical unit, the second optical
element B2 constitutes the second optical unit, the third optical
element B3 constitutes the third optical unit, and the fourth
optical element B4 constitutes the fourth optical unit. The second
and fourth optical units are magnification varying optical units
which vary the relative position therebetween to vary the
magnification of the variable magnification optical system.
[0310] An image forming operation for an object lying at infinity
will be described below. First, a light beam which has passed
through the first optical element B1 and the stop R3 in that order
enters the second optical element B2. In the second optical element
B2, the light beam is refracted by the fourth surface R4, then
reflected from surface to surface by the fifth surface R5 to the
eighth surface R8, then refracted by the ninth surface R9, and then
exits from the second optical element B2. During this time, a
primary image is formed in the vicinity of the sixth surface R6,
and a secondary image is formed between the eighth surface R8 and
the ninth surface R9. A pupil is formed in the vicinity of the
seventh surface R7.
[0311] Then, the light beam enters the third optical element B3. In
the third optical element B3, the light beam is refracted by the
tenth surface R10, then reflected from surface to surface by the
eleventh surface R11 to the fourteenth surface R14, then refracted
by the fifteenth surface R15, and then exits from the third optical
element B3. During this time, a tertiary image forming plane is
formed between the twelfth surface R12 and the thirteenth surface
R13 when the focal length is at the wide-angle end, or in the
vicinity of the thirteenth surface R13 when the focal length is at
the telephoto end. Another pupil is formed between the fourteenth
surface R14 and the fifteenth surface R15 at any focal length from
the wide-angle end to the telephoto end.
[0312] Then, the light beam enters the fourth optical element B4.
In the fourth optical element B4, the light beam is refracted by
the sixteenth surface R16, then reflected from surface to surface
by the seventeenth surface R17 to the twenty-first surface R21,
then refracted by the twenty-second surface R22, and then exits
from the fourth optical element B4. During this time, a quaternary
image forming plane is formed in the vicinity of the seventeenth
surface R17 when the focal length is at the wide-angle end, or
between the seventeenth surface R17 and the eighteenth surface R18
when the focal length is at the telephoto end. A pupil is formed in
the vicinity of the twentieth surface R20 when the focal length is
at the wide-angle end, or between the eighteenth surface R18 and
the nineteenth surface R19 when the focal length is at the
telephoto end.
[0313] The light beam which has exited from the fourth optical
element B4 passes through the twenty-third to twenty-seventh
surfaces R23 to R27, and finally forms an object image on the
twenty-eighth surface R28 which is a quinary image forming
plane.
[0314] In Numerical Example 1, the entering reference axis and the
exiting reference axis of each of the second optical element B2 and
the third optical element B3 are parallel to and the same as each
other in direction. The entering reference axis and the exiting
reference axis of the fourth optical element B4 are parallel to
each other, but differ from each other by 180.degree. in
direction.
[0315] The movements of the respective optical elements during a
magnification varying operation will be described below. During the
magnification varying operation, the first optical element B1 and
the stop R3 which constitute the first optical unit, the third
optical element B3 which constitutes the third optical unit, and
the block B5 are fixed and do not move. As the focal length varies
from the wide-angle end toward the telephoto end, the second
optical element B2 which constitutes the second optical unit moves
in the Z plus direction in parallel with the entering reference
axis of the second optical element B2. In the meantime, the fourth
optical element B4 which constitutes the fourth optical unit moves
in the Z plus direction in parallel with the entering reference
axis of the fourth optical element B4.
[0316] During the magnification varying operation, the filter, the
cover glass and the twenty-eighth surface R28 which is the final
image plane do not move.
[0317] Thus, as the focal length varies from the wide-angle end
toward the telephoto end, the distance between the second optical
element B2 and the third optical element B3 is decreased, the
distance between the third optical element B3 and the fourth
optical element B4 is increased, and the distance between the
fourth optical element B4 and the twenty-third surface R23 is
increased.
[0318] In addition, as the focal length varies from the wide-angle
end toward the telephoto end, the entire optical path length which
extends from the first surface R1 to the final image plane R28
becomes longer.
[0319] Each of FIGS. 16, 17 and 18 shows lateral aberration charts
of Numerical Example 1 relative to the wide-angle end (W), the
middle position (M) and the telephoto end (T). The respective
lateral aberration charts show lateral aberrations in the Y and X
directions, relative to six light beams which enter Numerical
Example 1 at different angles of incidence of (u.sub.Y, u.sub.X),
(0, u.sub.X), (-u.sub.Y, u.sub.X), (u.sub.Y, 0), (0, 0) and
(-u.sub.Y, 0), respectively. The horizontal axis of each of the
lateral aberration charts represents the height of incidence in the
Y or X direction of a light beam which is incident on each of the
entrance pupils.
[0320] As can be seen from these figures, Numerical Example 1 is
capable of achieving well-balanced correction of aberration at each
zoom position.
[0321] In addition, the optical system of Numerical Example 1 is
approximately 8.7 mm thick for an image size of 3.76 mm.times.2.82
mm. In Numerical Example 1, particularly because each of the
optical elements and the entire optical system has a small
thickness and each of the optical elements can be constructed by
forming reflecting surfaces on predetermined sides of a
plate-shaped transparent body, it is possible to readily construct
a variable magnification optical system which is thin as a whole,
by adopting a mechanism which causes two optical elements to move
along a surface of one base plate.
[0322] Incidentally, in Numerical Example 1, although a chromatic
aberration is caused by a plurality of refracting surfaces, the
curvature of each of the refracting surfaces is appropriately
determined so that the chromatic aberration is corrected over the
entire range of variation of magnification. In particular, an axial
chromatic aberration which occurs at the fourth surface R4 is fully
corrected by the negative lens disposed immediately in front of the
stop.
[0323] The values and its ratio of the lateral magnification of
each of the second optical element B2 to the fourth optical element
B4 relative to the wide-angle end and the telephoto end are shown
below. The values shown below are calculated by using the aforesaid
equation 19. An azimuth is contained in the Y, Z cross-sectional
plane (the surface of the sheet of the optical path diagram of FIG.
16).
2 WIDE-ANGLE TELEPHOTO END END (TELEPHOTO END)/(WIDE ANGLE END)
SECOND 0.189 0.169 0.894 OPTICAL ELEMENT THIRD 1.031 4.338 4.208
OPTICAL ELEMENT FOURTH -1.160 -0.778 0.671 OPTICAL ELEMENT
[0324] In Numerical Example 1, the third optical element B3 has the
largest magnification ratio.
[0325] The pupil distance from the final image plane to an exit
pupil is shown below. This value is calculated on the basis of the
previously described paraxial tracing of the off-axial optical
system. An azimuth is contained in the Y, Z cross-sectional plane
(the surface of the sheet of the optical path diagram of FIG.
16).
3 WIDE-ANGLE TELEPHOTO END END EXIT -15.394 144.549 PUPIL
DISTANCE
[0326] Incidentally, Numerical Example 1 is the variable
magnification optical system of the second embodiment shown in FIG.
4.
[0327] [Numerical Example 2]
[0328] Numerical Example 2 is a variable magnification optical
system having a magnification variation ratio of approximately
2.8.times.. FIGS. 19, 20 and 21 are cross-sectional views taken in
the Y, Z plane, showing the respective optical paths of Numerical
Example 2 relative to the wide-angle end (W), the middle position
(M) and the telephoto end (T).
[0329] Constituent data for Numerical Example 2 are shown
below.
4 WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END HORIZONTAL
HALF-ANGLE 27.3 19.0 9.8 OF VIEW VERTICAL HALF-ANGLE 21.2 14.5 7.4
OF VIEW APERTURE DIAMETER 1.30 1.40 2.40 i Yi Zi(W) .theta.i Di Ndi
.nu.di FIRST OPTICAL ELEMENT B1 (NEGATIVE LENS) 1 0.00 0.00 0.00
0.70 1.51633 64.15 2 0.00 0.70 0.00 2.00 1 3 0.00 2.70 0.00
VARIABLE 1 STOP SECOND OPTICAL ELEMENT B2 4 0.00 3.70 0.00 6.00
1.49171 57.40 REFRACTING SURFACE 5 0.00 9.70 30.00 7.30 1.49171
57.40 REFLECTING SURFACE 6 -6.32 6.05 30.00 7.10 1.49171 57.40
REFLECTING SURFACE 7 -6.32 13.15 30.00 7.60 1.49171 57.40
REFLECTING SURFACE 8 -12.90 9.35 30.00 10.00 1.49171 57.40
REFLECTING SURFACE 9 -12.90 19.35 0.00 VARIABLE 1 REFRACTING
SURFACE THIRD OPTICAL ELEMENT B3 10 -12.90 22.55 0.00 5.00 1.49171
57.40 REFRACTING SURFACE 11 -12.90 27.55 -30.00 8.00 1.49171 57.40
REFLECTING SURFACE 12 -5.98 23.55 -15.00 8.00 1.49171 57.40
REFLECTING SURFACE 13 -1.98 30.47 0.00 8.00 1.49171 57.40
REFLECTING SURFACE 14 2.02 23.55 15.00 8.00 1.49171 57.40
REFLECTING SURFACE 15 8.95 27.55 30.00 6.00 1 REFLECTING SURFACE 16
8.95 21.55 0.00 VARIABLE 1 REFRACTING SURFACE FOURTH OPTICAL
ELEMENT B4 17 8.95 19.14 0.00 6.00 1.49171 57.40 REFRACTING SURFACE
18 8.95 13.14 30.00 8.00 1.49171 57.40 REFLECTING SURFACE 19 15.88
17.14 15.00 8.00 1.49171 57.40 REFLECTING SURFACE 20 19.88 10.21
0.00 8.00 1.49171 57.40 REFLECTING SURFACE 21 23.88 17.14 -15.00
8.00 1.49171 57.40 REFLECTING SURFACE 22 30.81 13.14 -30.00 6.00
1.49171 57.40 REFLECTING SURFACE 23 30.81 19.14 0.00 VARIABLE 1
REFRACTING SURFACE BLOCK B5 24 30.81 20.33 0.00 2.08 1.51400 70.00
FILTER 25 30.81 22.41 0.00 1.60 1.52000 74.00 FILTER 26 30.81 24.01
0.00 1.00 1 27 30.81 25.01 0.00 0.80 1.51633 64.15 COVER GLASS 28
30.81 25.81 0.00 0.91 1 29 30.81 26.72 -0.00 1 IMAGE PLANE
WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END D3 1.00 2.24 3.60 D9
3.20 1.96 0.60 D16 2.40 3.50 7.21 D23 1.19 2.29 6.00 R1-R3 Zi(M) =
Zi(W) Zi(T) = Zi(W) R4-R9 Zi(M) = Zi(W) + 1.24 Zi(T) = Zi(W) + 2.60
R10-R16 Zi(M) = Zi(W) Zi(T) = Zi(W) R17-R23 Zi(M) = Zi(W) - 1.10
Zi(T) = Zi(W) - 4.81 R24 Zi(M) = Zi(W) Zi(T) = Zi(W) SPHERICAL
SHAPE R1 R.sub.1 = 6.178 R2 R.sub.2 = 3.575 R4 R.sub.4 = 8.000 R9
R.sub.9 = -8.094 R10 R.sub.10 = -14.301 R16 R.sub.16 = -14.930 R17
R.sub.17 = 7.534 R23 R.sub.23 = .infin. R24 R.sub.24 = .infin. R25
R.sub.25 = .infin. R26 R.sub.26 = .infin. R27 R.sub.27 = .infin.
R28 R.sub.28 = .infin. ASPHERICAL SHAPE R5 C.sub.02 = -2.10440e-02
C.sub.20 = -6.88526e-02 C.sub.03 = 1.83699e-03 C.sub.21 =
-1.46872e-03 C.sub.04 = 1.34949e-04 C.sub.22 = -5.82208e-04
C.sub.40 = -4.21790e-04 C.sub.05 = -5.37823e-06 C.sub.23 =
-8.37809e-05 C.sub.41 = 8.29155e-05 C.sub.06 = -5.56652e-06
C.sub.24 = -9.32652e-06 C.sub.42 = -3.09610e-05 C.sub.60 =
1.43427e-05 R6 C.sub.02 = 3.01751e-02 C.sub.20 = 4.05535e-02
C.sub.03 = -9.72322e-04 C.sub.21 = 6.66467e-03 C.sub.04 =
1.40569e-04 C.sub.22 = 1.32485e-04 C.sub.40 = 5.21673e-04 C.sub.05
= -4.72601e-05 C.sub.23 = -1.85290e-05 C.sub.41 = -8.53945e-05
C.sub.06 = 5.26656e-06 C.sub.24 = -3.79418e-06 C.sub.42 =
-1.36321e-05 C.sub.60 = -2.58044e-05 R7 C.sub.02 = -2.96565e-02
C.sub.20 = -2.25708e-02 C.sub.03 = 3.19727e-05 C.sub.21 =
-5.92886e-03 C.sub.04 = 2.14567e-04 C.sub.22 = 3.57027e-04 C.sub.40
= -1.22342e-04 C.sub.05 = -2.22202e-05 C.sub.23 = 9.98206e-06
C.sub.41 = 5.48399e-05 C.sub.06 = -6.53759e-05 C.sub.24 =
-5.28163e-05 C.sub.42 = -6.42052e-06 C.sub.60 = 9.43292e-07 R8
C.sub.02 = 5.12990e-02 C.sub.20 = 3.35016e-02 C.sub.03 =
-8.63164e-04 C.sub.21 = 1.89263e-03 C.sub.04 = 2.28926e-04 C.sub.22
= 7.22598e-05 C.sub.40 = 2.15995e-05 C.sub.05 = -2.81376e-06
C.sub.23 = 2.33569e-05 C.sub.41 = -1.61267e-05 C.sub.06 =
-7.57749e-07 C.sub.24 = 2.94772e-06 C.sub.42 = -8.62955e-06
C.sub.60 = -1.50908e-06 R11 C.sub.02 = -3.55122e-02 C.sub.20 =
-4.20556e-02 C.sub.03 = 3.14719e-05 C.sub.21 = -1.81869e-03
C.sub.04 = -5.61765e-05 C.sub.22 = -1.52031e-04 C.sub.40 =
-1.67091e-04 R12 C.sub.02 = -1.41192e-02 C.sub.20 = 6.11333e-03
C.sub.03 = -2.22136e-04 C.sub.21 = 2.26429e-03 C.sub.04 =
-1.40277e-04 C.sub.22 = -8.21339e-05 C.sub.40 = 4.34677e-04 R13
C.sub.02 = -2.17200e-02 C.sub.20 = -3.63945e-02 C.sub.03 =
2.99814e-04 C.sub.21 = -2.35042e-03 C.sub.04 = -5.77814e-05
C.sub.22 = -2.47845e-05 C.sub.40 = -1.35757e-04 R14 C.sub.02 =
-4.69754e-03 C.sub.20 = -3.30557e-02 C.sub.03 = -2.12404e-04
C.sub.21 = 9.87897e-03 C.sub.04 = 2.91489e-06 C.sub.22 =
1.45151e-03 C.sub.40 = 1.56530e-03 R15 C.sub.02 = -2.44735e-02
C.sub.20 = -4.32725e-02 C.sub.03 = 1.29214e-05 C.sub.21 =
-7.05429e-04 C.sub.04 = -3.96652e-05 C.sub.22 = -1.21232e-04
C.sub.40 = -8.53259e-05 R18 C.sub.02 = 2.46685e-02 C.sub.20 =
1.70099e-02 C.sub.03 = -1.07447e-04 C.sub.21 = 1.27814e-03 C.sub.04
= -4.75274e-05 C.sub.22 = -9.43105e-05 C.sub.40 = -9.11962e-05 R19
C.sub.02 = 1.91547e-02 C.sub.20 = 1.63259e-02 C.sub.03 =
-1.99806e-04 C.sub.21 = -1.01916e-03 C.sub.04 = 2.80852e-04
C.sub.22 = -8.00207e-04 C.sub.40 = -2.60931e-04 R20 C.sub.02 =
3.04540e-02 C.sub.20 = 3.95082e-02 C.sub.03 = -1.70729e-04 C.sub.21
= 7.35847e-04 C.sub.04 = 5.22719e-05 C.sub.22 = -2.48107e-06
C.sub.40 = 6.92769e-05 R21 C.sub.02 = 1.83456e-02 C.sub.20 =
6.39762e-02 C.sub.03 = 1.55164e-04 C.sub.21 = -5.22449e-03 C.sub.04
= 1.22578e-04 C.sub.22 = 7.47137e-05 C.sub.40 = 2.26637e-03 R22
C.sub.02 = 2.08626e-02 C.sub.20 = 3.52073e-02 C.sub.03 =
-2.21145e-04 C.sub.21 = -1.08183e-03 C.sub.04 = 1.82605e-05
C.sub.22 = 4.95072e-06 C.sub.40 = 1.59696e-04
[0330] The construction of Numerical Example 2 will be described
below. The first optical element B1 is a negative lens which has
the first surface R1 and the second surface R2, and the third
surface R3 is an aperture plane. The second optical element B2 is
formed as one transparent body on which the fourth surface R4
(entrance refracting surface), the fifth to eighth surfaces R5 to
R8 each of which is a decentered curved internal reflecting
surface, and the ninth surface R9 (exit refracting surface) are
formed. The third optical element B3 is formed as one transparent
body on which the tenth surface R10 (entrance refracting surface),
the eleventh to fifteenth surfaces R11 to R15 each of which is a
decentered curved internal reflecting surface, and the sixteenth
surface R16 (exit refracting surface) are formed. The fourth
optical element B4 is formed as one transparent body on which the
seventeenth surface R17 (entrance refracting surface), the
eighteenth to twenty-second surfaces R18 to R22 each of which is a
decentered curved internal reflecting surface, and the twenty-third
surface R23 (exit refracting surface) are formed.
[0331] The twenty-fourth to twenty-eighth surfaces R24 to R28 are
those of plane parallel plates such as a filter and a cover glass.
The surfaces R24 to R28 constitute the block B5. The twenty-ninth
surface R29 is a final image plane in which the image pickup
surface of an image pickup device such as a CCD is positioned.
[0332] The optical elements of Numerical Example 2 are grouped into
four optical units which constitute a variable magnification
optical system. Specifically, the first optical element B1 and the
stop R3 constitute the first optical unit, the second optical
element B2 constitutes the second optical unit, the third optical
element B3 constitutes the third optical unit, and the fourth
optical element B4 constitutes the fourth optical unit. The second
and fourth optical units are magnification varying optical units
which vary the relative position therebetween to vary the
magnification of the variable magnification optical system.
[0333] An image forming operation for an object lying at infinity
will be described below. First, a light beam which has passed
through the first optical element B1 and the stop R3 in that order
enters the second optical element B2. In the second optical element
B2, the light beam is refracted by the fourth surface R4, then
reflected from surface to surface by the fifth surface R5 to the
eighth surface R8, then refracted by the ninth surface R9, and then
exits from the second optical element B2. During this time, a
primary image is formed in the vicinity of the sixth surface R6,
and a secondary image is formed between the eighth surface R8 and
the ninth surface R9. A pupil is formed in the vicinity of the
seventh surface R7.
[0334] Then, the light beam enters the third optical element B3. In
the third optical element B3, the light beam is refracted by the
tenth surface R10, then reflected from surface to surface by the
eleventh surface R11 to the fifteenth surface R15, then refracted
by the sixteenth surface R16, and then exits from the third optical
element B3. During this time, a tertiary image forming plane is
formed between the twelfth surface R12 and the thirteenth surface
R13 when the focal length is at the wide-angle end, or in the
vicinity of the thirteenth surface R13 when the focal length is at
the telephoto end. A pupil is formed in the vicinity of the
fourteenth surface R14 when the focal length is at the wide-angle
end, or between the fourteenth surface R14 and the fifteenth
surface R15 when the focal length is at the telephoto end.
[0335] Then, the light beam enters the fourth optical element B4.
In the fourth optical element B4, the light beam is refracted by
the seventeenth surface R17, then reflected from surface to surface
by the eighteenth surface R18 to the twenty-second surface R22,
then refracted by the twenty-third surface R23, and then exits from
the fourth optical element B4. During this time, a quaternary image
forming plane is formed between the eighteenth surface R18 and the
nineteenth surface R19 when the focal length is at the wide-angle
end, or in the vicinity of the nineteenth surface R19 when the
focal length is at the telephoto end. A pupil is formed in the
vicinity of the twenty-first surface R21 at any focal length from
the wide-angle end to the telephoto end.
[0336] The light beam which has exited from the fourth optical
element B4 passes through the twenty-fourth to twenty-eighth
surfaces R24 to R28, and finally forms an object image on the
twenty-ninth surface R29 which is a quinary image forming
plane.
[0337] In Numerical Example 2, the entering reference axis and the
exiting reference axis of the second optical element B2 are
parallel to and the same as each other in direction. The entering
reference axis and the exiting reference axis of each of the third
optical element B3 and the fourth optical element B4 are parallel
to each other, but differ from each other by 180.degree. in
direction.
[0338] The movements of the respective optical elements during a
magnification varying operation will be described below. During the
magnification varying operation, the first optical element B1 and
the stop R3 which constitute the first optical unit, the third
optical element B3 which constitutes the third optical unit, and
the block B5 are fixed and do not move. As the focal length varies
from the wide-angle end toward the telephoto end, the second
optical element B2 which constitutes the second optical unit moves
in the Z plus direction in parallel with the entering reference
axis of the second optical element B2. In the meantime, the fourth
optical element B4 which constitutes the fourth optical unit moves
in the Z minus direction in parallel with the entering reference
axis of the fourth optical element B4.
[0339] During the magnification varying operation, the filter, the
cover glass and the twenty-ninth surface R29 which is the final
image plane do not move.
[0340] Thus, as the focal length varies from the wide-angle end
toward the telephoto end, the distance between the second optical
element B2 and the third optical element B3 is decreased, the
distance between the third optical element B3 and the fourth
optical element B4 is increased, and the distance between the
fourth optical element B4 and the twenty-fourth surface R24 is
increased.
[0341] In addition, as the focal length varies from the wide-angle
end toward the telephoto end, the entire optical path length which
extends from the first surface R1 to the final image plane R30
becomes longer.
[0342] FIGS. 22, 23 and 24 show lateral aberration charts of
Numerical Example 2 relative to the wide-angle end (W), the middle
position (M) and the telephoto end (T). The respective lateral
aberration charts show lateral aberrations in the Y and X
directions, relative to six light beams which enter Numerical
Example 2 at different angles of incidence of (u.sub.Y, u.sub.X),
(0, u.sub.X), (-u.sub.Y, u.sub.X), (u.sub.Y, 0), (0, 0) and
(-u.sub.Y, 0), respectively. The horizontal axis of each of the
lateral aberration charts represents the height of incidence in the
Y or X direction of a light beam which is incident on each of the
entrance pupils.
[0343] As can be seen from these figures, Numerical Example 2 is
capable of achieving well-balanced correction of aberration at each
zoom position.
[0344] In addition, the optical system of Numerical Example 2 is
approximately 7.4 mm thick for an image size of 3.76 mm.times.2.82
mm. In Numerical Example 2, particularly because each of the
optical elements and the entire optical system has a small
thickness and each of the optical elements can be constructed by
forming reflecting surfaces on predetermined sides of a
plate-shaped transparent body, it is possible to readily construct
a variable magnification optical system which is thin as a whole,
by adopting a mechanism which causes two optical elements to move
along a surface of one base plate.
[0345] Incidentally, in Numerical Example 2, although a chromatic
aberration is caused by a plurality of refracting surfaces, the
curvature of each of the refracting surfaces is appropriately
determined so that the chromatic aberration is corrected over the
entire range of variation of magnification. In particular, an axial
chromatic aberration which occurs at the fourth surface R4 is fully
corrected by the negative lens disposed immediately in front of the
stop.
[0346] The values and its ratio of the lateral magnification of
each of the second optical element B2 to the fourth optical element
B4 relative to the wide-angle end and the telephoto end are shown
below. The values shown below are calculated by using the aforesaid
equation 19. An azimuth is contained in the Y, Z cross-sectional
plane (the surface of the sheet of the optical path diagram of FIG.
19).
5 WIDE-ANGLE TELEPHOTO END END (TELEPHOTO END)/(WIDE-ANGLE END)
SECOND 0.212 0.190 0.896 OPTICAL ELEMENT THIRD 1.147 3.660 3.191
OPTICAL ELEMENT FOURTH -0.972 -0.858 0.883 OPTICAL ELEMENT
[0347] In Numerical Example 2, the third optical element B3 has the
largest magnification ratio.
[0348] The pupil distance from the final image plane to an exit
pupil is shown below. This value is calculated on the basis of the
previously described paraxial tracing of the off-axial optical
system. An azimuth is contained in the Y, Z cross-sectional plane
(the surface of the sheet of the optical path diagram of FIG.
19).
6 WIDE-ANGLE TELEPHOTO END END EXIT -13.202 -34.469 PUPIL
DISTANCE
[0349] Incidentally, Numerical Example 2 is the variable
magnification optical system in which the negative lens is provided
in front of the stop of the third embodiment shown in FIG. 5.
[0350] [Numerical Example 3]
[0351] Numerical Example 3 is a variable magnification optical
system having a magnification variation ratio of approximately
2.8.times.. FIGS. 25, 26 and 27 are cross-sectional views taken in
the Y, Z plane, showing the respective optical paths of Numerical
Example 3 relative to the wide-angle end (W), the middle position
(M) and the telephoto end (T).
[0352] Constituent data for Numerical Example 3 are shown
below.
7 WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END HORIZONTAL
HALF-ANGLE 26.0 18.0 9.2 OF VIEW VERTICAL HALF-ANGLE 20.0 13.6 6.9
OF VIEW APERTURE DIAMETER 1.30 1.60 2.40 i Yi Zi(W) .theta.i Di Ndi
.nu.di FIRST OPTICAL ELEMENT B1 (NEGATIVE LENS) 1 0.00 0.00 0.00
1.00 1.49700 81.61 2 0.00 1.00 0.00 3.00 1 3 0.00 4.00 0.00
VARIABLE 1 STOP SECOND OPTICAL ELEMENT B2 4 0.00 8.18 0.00 6.00
1.58312 59.37 REFRACTING SURFACE 5 0.00 14.18 30.00 8.00 1.58312
59.37 REFLECTING SURFACE 6 -6.93 10.18 15.00 8.00 1.58312 59.37
REFLECTING SURFACE 7 -10.93 17.11 0.00 8.00 1.58312 59.37
REFLECTING SURFACE 8 -14.93 10.18 -15.00 8.00 1.58312 59.37
REFLECTING SURFACE 9 -21.86 14.18 -30.00 12.00 1.58312 59.37
REFLECTING SURFACE 10 -21.86 2.18 0.00 VARIABLE 1 REFRACTING
SURFACE THIRD OPTICAL ELEMENT B3 11 -21.86 2.60 0.00 5.00 1.58312
59.37 REFRACTING SURFACE 12 -21.86 7.60 30.00 8.00 1.58312 59.37
REFLECTING SURFACE 13 -28.78 3.60 15.00 8.00 1.58312 59.37
REFLECTING SURFACE 14 -32.78 -10.52 0.00 8.00 1.58312 59.37
REFLECTING SURFACE 15 -36.78 3.60 15.00 8.00 1.58312 59.37
REFLECTING SURFACE 16 -43.71 7.60 30.00 6.00 1.58312 59.37
REFLECTING SURFACE 17 -43.71 1.60 0.00 VARIABLE 1 REFRACTING
SURFACE FOURTH OPTICAL ELEMENT B4 18 -43.71 2.75 0.00 6.00 1.58312
59.37 REFRACTING SURFACE 19 -43.71 8.75 30.00 8.00 1.58312 59.37
REFLECTING SURFACE 20 -50.64 4.75 15.00 8.00 1.58312 59.37
REFLECTING SURFACE 21 -54.64 11.68 0.00 8.00 1.58312 59.37
REFLECTING SURFACE 22 -58.64 4.75 15.00 8.00 1.58312 59.37
REFLECTING SURFACE 23 -65.57 8.75 30.00 6.00 1.58312 59.37
REFLECTING SURFACE 24 -65.57 2.75 0.00 VARIABLE 1 REFRACTING
SURFACE BLOCK B5 25 -65.57 0.33 0.00 2.08 1.51400 70.00 FILTER 26
-65.57 1.75 0.00 1.60 1.52000 74.00 FILTER 27 -65.57 3.35 0.00 1.00
1 28 -65.57 4.35 0.00 0.80 1.51633 64.15 COVER GLASS 29 -65.57 5.15
0.00 0.91 1 30 -65.57 6.06 -0.00 1 IMAGE PLANE WIDE-ANGLE MIDDLE
TELEPHOTO END POSITION END D3 4.18 2.65 0.46 D10 4.77 3.24 1.06 D17
4.34 5.45 9.72 D24 2.42 3.53 7.79 R1-R3 Zi(M) = Zi(W) Zi(T) = Zi(W)
R4-R10 Zi(M) = Zi(W) - 1.53 Zi(T) = Zi(W) - 3.72 R11-R17 Zi(M) =
Zi(W) Zi(T) = Zi(W) R18-R24 Zi(M) = Zi(W) + 1.11 Zi(T) = Zi(W) +
5.37 R25 Zi(M) = Zi(W) Zi(T) = Zi(W) SPHERICAL SHAPE R.sub.1
R.sub.1 = .infin. R2 R.sub.2 = 10.000 R4 R.sub.4 = 10.000 R10
R.sub.10 = 6.000 R11 R.sub.11 = 30.000 R17 R.sub.17 = 16.000 R18
R.sub.18 = -16.000 R24 R.sub.24 = .infin. R25 R.sub.25 = .infin.
R26 R.sub.26 = .infin. R27 R.sub.27 = .infin. R28 R.sub.28 =
.infin. R29 R.sub.29 = .infin. ASPHERICAL SHAPE R5 C.sub.02 =
-2.76771e-02 C.sub.20 = -3.38475e-02 C.sub.03 = 8.72588e-05
C.sub.21 = 1.27014e-03 C.sub.04 = 9.91343e-05 C.sub.22 =
2.88418e-06 C.sub.40 = 1.95838e-04 R6 C.sub.02 = -1.33887e-02
C.sub.20 = -3.29802e-02 C.sub.03 = -4.34730e-04 C.sub.21 =
-1.56119e-02 C.sub.04 = -3.34908e-04 C.sub.22 = 1.13638e-04
C.sub.40 = 3.54554e-03 R7 C.sub.02 = -2.76384-02 C.sub.20 =
-4.00638e-02 C.sub.03 = -4.21455e-04 C.sub.21 = 1.38350e-04
C.sub.04 = -6.85970e-05 C.sub.22 = -3.26960e-05 C.sub.40 =
-1.32135e-04 R8 C.sub.02 = -6.69839e-04 C.sub.20 = -3.41563e-03
C.sub.03 = 1.64573e-04 C.sub.21 = 2.45641e-03 C.sub.04 =
-5.36361e-05 C.sub.22 = -2.12330e-04 C.sub.40 = -6.79401e-04 R9
C.sub.02 = -3.02725e-02 C.sub.20 = -4.88968e-02 C.sub.03 =
2.65523e-04 C.sub.21 = 6.32978e-04 C.sub.04 = -1.32703e-04 C.sub.22
= 1.36494e-04 C.sub.40 = -1.26186e-04 R12 C.sub.02 = 3.15601e-02
C.sub.20 = 4.15702e-02 C.sub.03 = 1.14258e-04 C.sub.21 =
7.07101e-04 C.sub.04 = 1.34163e-05 C.sub.22 = 7.32145e-05 C.sub.40
= 9.20123e-05 R13 C.sub.02 = 2.52923e-04 C.sub.20 = 1.25782e-02
C.sub.03 = 5.54522e-04 C.sub.21 = 1.12824e-02 C.sub.04 =
4.04731e-05 C.sub.22 = -3.835520e-04 C.sub.40 = -2.60477e-04 R14
C.sub.02 = 2.53658e-02 C.sub.20 = 4.67700e-02 C.sub.03 =
-7.25493e-04 C.sub.21 = 3.83906e-03 C.sub.04 = -1.17824e-04
C.sub.22 = 9.40586e-05 C.sub.40 = 1.88707e-04 R15 C.sub.02 =
-1.44253e-03 C.sub.20 = 3.51310e-03 C.sub.03 = -3.30632e-04
C.sub.21 = -8.16892e-04 C.sub.04 = 7.74891e-06 C.sub.22 =
-1.02950e-04 C.sub.40 = 3.13600e-04 R16 C.sub.02 = 1.82845e-02
C.sub.20 = 2.24423e-02 C.sub.03 = -1.24310e-04 C.sub.21 =
1.54839e-03 C.sub.04 = 4.33331e-05 C.sub.22 = 1.05157e-04 C.sub.40
= 8.03684e-05 R19 C.sub.02 = -2.31259e-02 C.sub.20 = -3.24017e-02
C.sub.03 = 2.36012e-04 C.sub.21 = 5.79554e-04 C.sub.04 =
-1.77382e-05 C.sub.22 = -6.03475e-05 C.sub.40 = -8.56820e-05 R20
C.sub.02 = -2.33043e-02 C.sub.20 = -6.17797e-02 C.sub.03 =
6.98278e-04 C.sub.21 = 8.01837e-03 C.sub.04 = 1.59521e-04 C.sub.22
= -1.91837e-04 C.sub.40 = 3.96353e-03 R21 C.sub.02 = -2.89424e-02
C.sub.20 = -3.42028e-02 C.sub.03 = -7.45218e-05 C.sub.21 =
-2.41487e-04 C.sub.04 = -3.79400e-06 C.sub.22 = -1.45880e-04
C.sub.40 = -7.80549e-05 R22 C.sub.02 = -2.14031e-02 C.sub.20 =
-3.63620-02 C.sub.03 = -1.52231e-03 C.sub.21 = -9.02231e-04
C.sub.04 = -2.27125e-04 C.sub.22 = -2.01910e-04 C.sub.40 =
-3.56618e-04 R23 C.sub.02 = -2.18555e-02 C.sub.20 = -3.11135-02
C.sub.03 = -1.02866e-04 C.sub.21 = -1.08499e-04 C.sub.04 =
-2.44313e-05 C.sub.22 = -3.44400e-05 C.sub.40 = -4.75047e-05
[0353] The construction of Numerical Example 3 will be described
below. The first optical element B1 is a negative lens which has
the first surface R1 and the second surface R2, and the third
surface R3 is an aperture plane. The second optical element B2 is
formed as one transparent body on which the fourth surface R4
(entrance refracting surface), the fifth to ninth surfaces R5 to R9
each of which is a decentered curved internal reflecting surface,
and the tenth surface R10 (exit refracting surface) are formed. The
third optical element B3 is formed as one transparent body on which
the eleventh surface R11 (entrance refracting surface), the twelfth
to sixteenth surfaces R12 to R16 each of which is a decentered
curved internal reflecting surface, and the seventeenth surface R17
(exit refracting surface) are formed. The fourth optical element B4
is formed as one transparent body on which the eighteenth surface
R18 (entrance refracting surface), the nineteenth to twenty-third
surfaces R19 to R23 each of which is a decentered curved internal
reflecting surface, and the twenty-fourth surface R24 (exit
refracting surface) are formed.
[0354] The twenty-fifth to twenty-ninth surfaces R25 to R29 are
those of plane parallel plates such as a filter and a cover glass.
The surfaces R25 to R29 constitute the block B5. The thirtieth
surface R30 is a final image plane in which the image pickup
surface of an image pickup device such as a CCD is positioned.
[0355] The optical elements of Numerical Example 3 are grouped into
four optical units which constitute a variable magnification
optical system. Specifically, the first optical element B1 and the
stop R3 constitute the first optical unit, the second optical
element B2 constitutes the second optical unit, the third optical
element B3 constitutes the third optical unit, and the fourth
optical element B4 constitutes the fourth optical unit. The second
and fourth optical units are magnification varying optical units
which vary the relative position therebetween to vary the
magnification of the variable magnification optical system.
[0356] An image forming operation for an object lying at infinity
will be described below. First, a light beam which has passed
through the first optical element B1 and the stop R3 in that order
enters the second optical element B2. In the second optical element
B2, the light beam is refracted by the fourth surface R4, then
reflected from surface to surface by the fifth surface R5 to the
ninth surface R9, then refracted by the tenth surface R10, and then
exits from the second optical element B2. During this time, a
primary image is formed in the vicinity of the sixth surface R6,
and a secondary image is formed between the ninth surface R9 and
the tenth surface R10. A pupil is formed in the vicinity of the
eighth surface R8.
[0357] Then, the light beam enters the third optical element B3. In
the third optical element B3, the light beam is refracted by the
eleventh surface R11, then reflected from surface to surface by the
twelfth surface R12 to the sixteenth surface R16, then refracted by
the seventeenth surface R17, and then exits from the third optical
element B3. During this time, a tertiary image forming plane is
formed between the thirteenth surface R13 and the fourteenth
surface R14 when the focal length is at the wide-angle end, or in
the vicinity of the fourteenth surface R14 when the focal length is
at the telephoto end. A pupil is formed between the fifteenth
surface R15 and the sixteenth surface R16 when the focal length is
at the wide-angle end, or in the vicinity of the fourteenth surface
R14 when the focal length is at the telephoto end.
[0358] Then, the light beam enters the fourth optical element B4.
In the fourth optical element B4, the light beam is refracted by
the eighteenth surface R18, then reflected from surface to surface
by the nineteenth surface R19 to the twenty-third surface R23, then
refracted by the twenty-fourth surface R24, and then exits from the
fourth optical element B4. During this time, a quaternary image
forming plane is formed between the nineteenth surface R19 and the
twentieth surface R20 when the focal length is at the wide-angle
end, or in the vicinity of the twentieth surface R20 when the focal
length is at the telephoto end. A pupil is formed in the vicinity
of the twenty-second surface R22 when the focal length is at the
wide-angle end, or in the vicinity of the twenty-third surface R23
when the focal length is at the telephoto end.
[0359] The light beam which has exited from the fourth optical
element B4-passes through the twenty-fifth to twenty-ninth surfaces
R25 to R29, and finally forms an object image on the thirtieth
surface R30 which is a quinary image forming plane.
[0360] In Numerical Example 3, the entering reference axis and the
exiting reference axis of each of the second optical element B2,
the third optical element B3 and the fourth optical element B4 are
parallel to each other, but differ from each other by 180.degree.
in direction.
[0361] The movements of the respective optical elements during a
magnification varying operation will be described below. During the
magnification varying operation, the first optical element B1 and
the stop R3 which constitute the first optical unit, the third
optical element B3, and the block B5 are fixed and do not move. As
the focal length varies from the wide-angle end toward the
telephoto end, the second optical element B2 moves in the Z minus
direction in parallel with the entering reference axis of the
second optical element B2. In the meantime, the fourth optical
element B4 moves in the Z plus direction in parallel with the
entering reference axis of the fourth optical element B4.
[0362] During the magnification varying operation, the filter, the
cover glass and the thirtieth surface R30 which is the final image
plane do not move.
[0363] Thus, as the focal length varies from the wide-angle end
toward the telephoto end, the distance between the second optical
element B2 and the third optical element B3 is decreased, the
distance between the third optical element B3 and the fourth
optical element B4 is increased, and the distance between the
fourth optical element B4 and the twenty-fifth surface R25 is
increased.
[0364] In addition, as the focal length varies from the wide-angle
end toward the telephoto end, the entire optical path length which
extends from the first surface R1 to the final image plane R30
becomes temporarily shorter and then longer.
[0365] FIGS. 28, 29 and 30 show lateral aberration charts of
Numerical Example 3 relative to the wide-angle end (W), the middle
position (M) and the telephoto end (T). The respective lateral
aberration charts show lateral aberrations in the Y and X
directions, relative to six light beams which enter Numerical
Example 3 at different angles of incidence of (u.sub.Y, u.sub.X),
(0, u.sub.X) (-u.sub.Y, u.sub.X), (u.sub.Y, 0), (0, 0) and
(-u.sub.Y, 0), respectively. The horizontal axis of each of the
lateral aberration charts represents the height of incidence in the
Y or X direction of a light beam which is incident on each of the
entrance pupils.
[0366] As can be seen from these figures, Numerical Example 3 is
capable of achieving well-balanced correction of aberration at each
zoom position.
[0367] In addition, the optical system of Numerical Example 3 is
approximately 9.1 mm thick for an image size of 3.76 mm.times.2.82
mm. In Numerical Example 3, particularly because each of the
optical elements and the entire optical system has a small
thickness and each of the optical elements can be constructed by
forming reflecting surfaces on predetermined sides of a
plate-shaped transparent body, it is possible to readily construct
a variable magnification optical system which is thin as a whole,
by adopting a mechanism which causes two optical elements to move
along a surface of one base plate.
[0368] Incidentally, in Numerical Example 3, although a chromatic
aberration is caused by a plurality of refracting surfaces, the
curvature of each of the refracting surfaces is appropriately
determined so that the chromatic aberration is corrected over the
entire range of variation of magnification. In particular, an axial
chromatic aberration which occurs at the fourth surface R4 is fully
corrected by the negative lens disposed immediately in front of the
stop.
[0369] The values and its ratio of the lateral magnification of
each of the second optical element B2 to the fourth optical element
B4 relative to the wide-angle end and the telephoto end are shown
below. The values shown below are calculated by using the aforesaid
equation 19. An azimuth is contained in the Y, Z cross-sectional
plane (the surface of the sheet of the optical path diagram of FIG.
25).
8 WIDE-ANGLE TELEPHOTO END END (TELEPHOTO END)/(WIDE-ANGLE END)
SECOND 0.231 0.269 1.164 OPTICAL ELEMENT THIRD 1.190 4.010 3.370
OPTICAL ELEMENT FOURTH -0.742 -0.539 0.726 OPTICAL ELEMENT
[0370] In Numerical Example 3, the third optical element B3 has the
largest magnification ratio.
[0371] Incidentally, Numerical Example 3 is the variable
magnification optical system in which the negative lens is provided
in front of the stop of the fourth embodiment shown in FIG. 6.
[0372] Incidentally, if the first optical unit is not a fixed lens
but a moving optical unit, the aforesaid ratio of (the lateral
magnification at the telephoto end) to (the lateral magnification
at the wide-angle end) becomes "1" because of the same image
forming magnification.
[0373] Since a fixed optical unit is provided in the variable
magnification optical system according to the present invention, if
the fixed optical unit is formed as a transparent body on which an
entrance refracting surface, a plurality of internal reflecting
surfaces each of which is a decentered curved surface, and an
exiting reference axis are formed, the exiting reference axis can
be inclined by an arbitrary angle with respect to the entering
reference axis. Accordingly, the degree of freedom of layout with
which the variable magnification optical system is to be arranged
on one base plate is extremely increased.
[0374] Since each of Numerical Examples 1 to 3 is constructed in
such a manner that an object image is formed at least twice in a
variable magnification optical system, the thickness of the
variable magnification optical system can be made small in spite of
its wide angle of view. In addition, since decentered concave
reflecting surfaces are provided in the moving optical unit (the
moving optical unit B) lying on the image-plane side of the fixed
optical unit, and also in another optical unit, the optical path in
the variable magnification optical system is bent into a desired
shape so that the entire length of the variable magnification
optical system is reduced in a predetermined direction.
Furthermore, the reflecting surfaces of the moving optical unit B
are formed to have cross sections which are asymmetrical in a plane
containing the entering reference axis and the exiting reference
axis. Accordingly, the variable magnification optical system can be
realized as a small-sized high-performance variable magnification
optical system which is fully corrected for decentering aberration
over the entire range of variation of magnification.
[0375] In accordance with the present invention having the
aforesaid arrangement and construction, a variable magnification
optical system, in which at least three optical units, a moving
optical unit, a fixed optical unit and a moving optical unit are
arranged in that order from an object side and the magnification of
the variable magnification optical system is varied by the relative
movement between the two moving optical units, can be realized as a
high-performance variable magnification optical system which is
capable of varying the magnification while varying the optical path
length from an object to a final image plane-with the final image
forming plane spatially fixed, so that the thickness of the
variable magnification optical system is small in spite of its wide
angle of view and its entire length is short in a predetermined
direction as well as its decentering aberration is fully corrected
over the entire range of variation of magnification. In addition,
an image pickup apparatus using such high-performance variable
magnification optical system is achieved.
[0376] In addition, it is possible to achieve a variable
magnification optical system having at least one of the following
effects and advantages, and an image pickup apparatus employing
such a variable magnification optical system.
[0377] Since a stop is arranged on the object side of the variable
magnification optical system or in the vicinity of the first
surface and an object image is formed by a plurality of times in
the variable magnification optical system, the effective diameter
and the thickness of the variable magnification optical system can
be made small in spite of its wide angle of view.
[0378] Since each optical unit employs an optical element having a
plurality of reflecting surfaces having appropriate refractive
powers and the reflecting surfaces are arranged in a decentered
manner, the optical path in the variable magnification optical
system can be bent into a desired shape to reduce the entire length
of the variable magnification optical system in a predetermined
direction.
[0379] A plurality of optical elements which constitute the
variable magnification optical system are each formed as a
transparent body on which two refracting surfaces and a plurality
of reflecting surfaces are integrally formed in such a manner that
each of the reflecting surfaces is arranged in a decentered manner
and is given an appropriate refractive power. Accordingly, the
decentering aberration of the variable magnification optical system
can be fully corrected over the entire range of variation of
magnification.
[0380] Since each magnification varying optical unit employs an
optical element which is formed as a transparent body on which two
refracting surfaces and a plurality of curved or plane reflecting
surfaces are integrally formed, not only is it possible to reduce
the entire size of the variable magnification optical system, but
it is also possible to solve the problem of excessively strict
arrangement accuracy (assembly accuracy) which would have often
been experienced with reflecting surfaces.
[0381] A variator optical unit which shows a largest amount of
variation of magnification during a magnification varying operation
is fixed, and an optical unit lying on the object side of the
variator optical unit is moved to vary the magnification of the
variable magnification optical system, so that an exit pupil on its
telephoto side can be formed at a position more distant from an
image plane than that on its wide-angle side. Accordingly, by
appropriately setting the position of the exit pupil at the
wide-angle end, it is possible to restrain occurrence of shading
over the entire range of variation of magnification in an image
pickup apparatus employing a solid-state image pickup device.
[0382] A variator optical unit which shows a largest amount of
variation of magnification during a magnification varying operation
is composed of an optical element having an entering reference axis
and an exiting reference axis which differ from each other by
180.degree. in direction. The variator optical unit is fixed, and
an optical unit lying on the object side of the variator optical
unit is moved to vary the magnification of the variable
magnification optical system, so that the distance of movement of a
moving optical unit positioned on the image-plane side of the
variator optical unit can be reduced.
[0383] Yet another embodiment will be described below.
[0384] FIG. 43 is an explanatory view showing a variable
magnification optical system according to the present invention in
the form of a coaxial refracting optical system. The variable
magnification optical system shown in FIG. 43 includes the stop 11
and the first optical unit 12 which is fixed during a magnification
varying operation and has a positive refractive power, and the
intermediate image 13 is formed by the first optical unit 12. The
variable magnification optical system also includes the second
optical unit 14 and the third optical unit 15 which moves relative
to each other to perform the magnification varying operation. A
solid-state image pickup device or the like is disposed in the
final image forming plane (final image plane) 16.
[0385] The image forming operation of the variable magnification
optical system will be described below.
[0386] A light beam which has passed through the stop 11 forms the
intermediate image 13 by means of the first optical unit 12. The
intermediate image 13 becomes an object point for a combined system
consisting of the second optical unit 14 and the third optical unit
15, and such combined system serves as a finite-distance image
forming optical system to again form an image on the final image
forming plane 16. The second and third optical units 14 and 15 move
relative to each other to vary the image forming magnification of
the combined system, thereby varying the image forming
magnification of the variable magnification optical system.
[0387] FIG. 44 is a view of the optical arrangement of a fifth
embodiment of the variable magnification optical system according
to the present invention. The optical arrangement shown in FIG. 44
includes the first optical unit 12, the second optical unit 14 and
the third optical unit 15 each of which has a plurality of
reflecting surfaces which are inclined with respect to the
reference axis. In FIG. 44, although the first to third optical
units are schematically shown, their reflecting surfaces are not
shown. A dot-dashed line represents a principal ray which passes
through the first to third optical units while being repeatedly
reflected by the reflecting surfaces (not shown) in each of the
optical units, and reaches the center of the final image forming
plane 16. As is apparent from the above description, the variable
magnification optical system according to the present invention is
composed of optical units each having decentered reflecting
surfaces, and an optical axis similar to that of the coaxial
optical system does not definitely exist. For this reason, as
described previously, a ray which passes through the center of the
stop of the variable magnification optical system and reaches the
center of the final image forming plane is determined as a
reference axis ray, and the reference axis ray is defined as a
reference axis.
[0388] In the variable magnification optical system of the fifth
embodiment, the stop 11 is disposed on the object side of the first
optical unit 12 or in the vicinity of the first surface, and
reflecting surfaces are used in the first optical unit 12 so as to
collect a light beam, so that the first optical unit 12 can be made
a thin optical system having a small effective diameter. In
addition, since each of the second optical unit 14 and the third
optical unit 15 is composed of decentered reflecting surfaces, the
intermediate image formed by the first optical unit 12 can be
relayed (again formed) by a compact arrangement. Accordingly, the
variable magnification optical system of the fifth embodiment can
be realized as a variable magnification optical system which is
thin in spite of its wide angle of view, as will be described later
in several numerical examples. Incidentally, the "thickness of an
optical system" referred to herein means the thickness taken in a
direction perpendicular to the surface of the sheet of FIG. 44, and
the term "thin" or similar expressions used herein mean that such
thickness is small.
[0389] The magnification varying operation of the variable
magnification optical system shown in FIG. 44 will be described
below. FIG. 44 is a view showing that the variable magnification
optical system is set to the wide-angle end. The second optical
unit 14 and the third optical unit 15 move independently of each
other, for example, in the directions of the respective arrows,
thereby effecting a magnification varying operation. During the
magnification varying operation, as the focal length varies from
the wide-angle end to the telephoto end, the distance between the
first optical unit 12 and the second optical unit 14 is decreased,
while the distance between the third optical unit 15 and the image
plane 16 is increased. Each optical unit which is responsible for
the magnification varying operation is called the magnification
varying optical unit, and all the optical units from the
magnification varying optical unit which is closest to the object
side to the magnification varying optical unit closest to the image
side are collectively called the magnification varying portion.
[0390] Letting d1 be the amount of movement of the second optical
unit 14 and d2 the amount of movement of the third optical unit 15,
and letting L.sub.W be the value of the optical path length from
the first surface numbered from the object side of the variable
magnification optical system to the final image forming plane 16
when the focal length is at the wide-angle end, and letting L.sub.T
be the value of such optical path length when the focal length is
at the telephoto end, if the following condition is satisfied:
L.sub.T=L.sub.W+2(d2-d1), (Condition 1)
[0391] the final image forming plane 16 can be fixed at a constant
position in the arrangement shown in FIG. 44 even during the
magnification varying operation.
[0392] If d1 and d2 are not equal in Condition 1, i.e., the amounts
of movements of the second optical unit 14 and the third optical
unit 15 are not equal, the entire optical length L of the entire
variable magnification optical system varies. To satisfy Condition
1, in the variable magnification optical system of the fifth
embodiment, the magnification varying optical units 14 and 15 are
cooperatively assembled, and each of the magnification varying
optical units 14 and 15 is constructed in such a manner that its
entering reference axis and its exiting reference axis differ from
each other by 180.degree. in direction. In this arrangement and
construction, since the optical path length of the entire variable
magnification optical system can be varied with the final image
forming plane 16 physically fixed, there is no need to move an
image pickup device provided with electrical wiring or the like, so
that the construction of the entire image pickup apparatus can be
simplified.
[0393] The variable magnification optical system of the fifth
embodiment repeats intermediate image formation to form an
aberration-corrected image on the final image forming plane. Since
a pupil is present between each of the intermediate image forming
planes and the adjacent one, the variable magnification optical
system of the fifth embodiment repeats pupil image formation to
form an exit pupil relative to the entire variable magnification
optical system. To correct the off-axial distortion of such optical
system, it is preferable that a principal ray which symmetrically
enters from an object plane at each angle of view repeats image
formation from one pupil plane to another while maintaining the
symmetry of the principal ray. In other words, it is necessary to
correctly relay both image formation and pupil formation relative
to an object image. The fifth embodiment of the variable
magnification optical system has the basic arrangement in which
each of the magnification varying optical units has at least three
decentered concave reflecting surfaces each having a positive
refractive power. Such basic arrangement can compatibly realize
image formation and pupil formation and can also realize a thin
variable magnification optical system.
[0394] The fifth embodiment of the variable magnification optical
system according to the present invention has the aforesaid
decentered reflecting surfaces and, therefore, suffer various
decentering aberrations. To correct these decentering aberrations
over the entire range of variation of magnification, it is
necessary to correct the decentering aberrations in the respective
optical units or to make the decentering aberrations cancel one
another among the optical units. Although the object point of each
of the magnification varying optical units moves during a
magnification varying operation, it is generally difficult to
correct a decentering aberration in the corresponding optical unit
itself irrespective of the movement of the object point. For this
reason, the concave reflecting surfaces of each of the
magnification varying optical units of the fifth embodiment have
cross-sectional shapes which are asymmetrical on the surface of the
sheet of FIG. 44, so that the decentering aberration is corrected
as fully as possible in the corresponding optical unit with respect
to a particular object point. In addition, decentering aberration
variations due to the movement of the object point are made to
cancel one another among the optical units. Thus, the variable
magnification optical system is capable of correcting the
decentering aberrations over the entire range of variation of
magnification.
[0395] The basic arrangement of a magnification varying optical
unit suitable for use in the variable magnification optical system
of the fifth embodiment will be described below. FIG. 45 is a view
showing the basic arrangement of such magnification varying optical
unit in the form of a coaxial refracting optical system. The
optical system shown in FIG. 45 is an optical system which causes a
light beam entering from an object point to exit as a parallel
light beam. In FIG. 45, reference numeral 31 denotes an object
plane of the magnification varying optical unit, reference numerals
32 and 34 denote surfaces each having a positive refractive power,
reference numeral 33 denotes a pupil plane in a combined system 38
consisting of surfaces 32 and 34, and reference numeral 35 denotes
an image forming plane of the combined system 38 consisting of the
surfaces 32 and 34. Reference numeral 36 denotes a surface having a
positive refractive power for forming the light beam from the image
forming plane 35 into a parallel light beam. Reference numeral 37
denotes a pupil plane which is formed as an image of the pupil 33
by a combined system 39 consisting of the surfaces 34 and 36. If
the focal lengths of the surfaces 32, 34 and 36 are the same and
the distance between each of them is the same as the focal length,
each of the combined systems 38 and 39 becomes a life-size optical
system having a symmetrical arrangement. If such a life-size
optical system is repeatedly arranged, an image can be relayed
through a certain effective diameter. Accordingly, such repeated
arrangement of the life-size optical system is suited to a thin
optical system. In addition, since power surfaces are symmetrically
arranged, off-axial aberration is cancelled, so that both image
formation and pupil formation can be correctly relayed.
[0396] FIG. 46 is a view similar to FIG. 45 and shows, in the form
of a coaxial system, another basic arrangement of the magnification
varying optical unit of the fifth embodiment of the variable
magnification optical system according to the present invention. In
FIG. 46, the arrangement of image forming planes and pupil planes
is opposite to that of FIG. 45. In FIG. 46, reference numeral 41
denotes a pupil plane, reference numeral 42 denotes a surface
having a positive refractive power for forming a parallel light
beam from an object plane of the magnification varying optical unit
which is at infinity, reference numeral 43 denotes an image forming
plane formed by the surface 42, reference numerals 44 and 46 denote
surfaces each having a positive refractive power, reference numeral
45 denotes a pupil plane formed by a combined system 48 consisting
of the surfaces 42 and 44, and reference numeral 47 denotes an
image forming plane which is formed with respect to the image
forming plane 43 by a combined system 49 consisting of the surfaces
44 and 46. In FIG. 46 as well, if the focal lengths of the surfaces
42, 44 and 46 are the same and the distance between each of them is
the same as the focal length similarly to FIG. 45, each of the
combined systems 48 and 49 becomes a life-size optical system
having a symmetrical arrangement, so that both image formation and
pupil formation can be correctly relayed.
[0397] If the respective optical systems shown in FIGS. 45 and 46
are applied to the second optical unit 14 and the third optical
unit 15 shown in FIG. 43, a relay optical system having a lateral
magnification of 1.times. is formed by a combined system consisting
of the second optical unit 14 and the third optical unit 15. If the
entire variable magnification optical system is to be made thin,
that state may be applied to the wide-angle end. Letting Z be a
magnification variation ratio, if the magnification varying portion
is designed so that the second optical unit 14 and the third
optical unit 15 are moved in such a manner that the lateral
magnification of their combined system becomes Z at the telephoto
end, it is possible to realize a magnification varying portion
which is capable of maintaining the thickness of the variable
magnification optical system even at the wide-angle end. The
variable magnification optical system according to the present
invention is basically formed by assembling decentered reflecting
surfaces on the basis of the aforesaid power arrangement.
[0398] FIGS. 47(A) and 47(B) are explanatory views of the basic
arrangement of a magnification varying optical unit for the
variable magnification optical system of the fifth embodiment. The
shown magnification varying optical unit has the arrangement shown
in FIG. 45 and is composed of decentered reflecting surfaces. In
each of FIGS. 47(A) and 47(B), reference numeral 51 denotes an
object plane of the magnification varying optical unit, reference
numerals 52 and 54 denote concave reflecting surfaces, reference
numeral 53 denotes a pupil in a combined system consisting of the
concave reflecting surfaces 52 and 54, reference numeral 55 denotes
an intermediate image forming plane formed by a combined system
consisting of the concave reflecting surfaces 52 and 54, reference
numeral 56 denotes a concave reflecting surface, and reference
numeral 57 denotes a pupil which is an image of the pupil plane 53
formed by a combined system consisting of the concave reflecting
surfaces 54 and 56. The dot-dashed line shown in each of FIGS.
47(A) and 47(B) represents the aforesaid reference axis ray, and
the dot-dashed line of FIG. 47(A) represents the optical path of an
object ray passing through the center of the angle of view, while
the dot-dashed line of FIG. 47(B) represents the optical path of a
pupil ray (principal ray). Incidentally, in the arrangement shown
in each of FIGS. 47(A) and 47(B), the distance between each of the
object plane 51, the concave reflecting surface 52, the pupil plane
53, the concave reflecting surface 54, the image forming plane 55,
the concave reflecting surface 56 and the pupil plane 57 is
equal.
[0399] In the arrangement shown in each of FIGS. 47(A) and 47(B),
the focal length of each reflecting surface is determined by the
angle of incidence of the reference axis on the reflecting surface
and the curvature thereof at the intersection of the reference axis
and the reflecting surface, as described previously. Accordingly,
innumerable combinations of the angle of incidence and the
curvature are present with respect to a particular focal length.
However, if off-axial aberration is to be cancelled between the
combined system consisting of the reflecting surfaces 52 and 54 and
the combined system consisting of the concave reflecting surfaces
54 and 56, the shapes of the reflecting surfaces 52, 54 and 56
preferably have symmetry. For this reason, the reflecting surfaces
52, 54 and 56 preferably have the same curvature. To make the focal
lengths of the reflecting surfaces equal to one another, the angle
of incidence of the reference axis on each surface needs to be made
equal at .theta. (or 2.theta. in the case of the angle of the
entering reference axis and the exiting reference axis).
[0400] However, in such an arrangement, it is impossible to
construct the magnification varying optical unit in such a manner
that its entering reference axis and its exiting reference axis of
the magnification varying optical unit differ from each other by
180.degree. in direction. Such a magnification varying optical unit
cannot be applied to the second optical unit 14 shown in FIG.
44.
[0401] For the above-described reason, in the magnification varying
optical unit of the variable magnification optical system of the
fifth embodiment, five reflecting surfaces are formed by inserting
a ray-folding reflecting surface between each of the three concave
reflecting surfaces shown in each of FIGS. 47(A) and 47(B), so that
the entering reference axis and the exiting reference axis of the
magnification varying optical unit differ from each other by
180.degree. in direction with the angle of incidence of the
reference axis on each of the concave reflecting surfaces being
equal.
[0402] The construction of the magnification varying optical unit
of the fifth embodiment will be described below with reference to
FIGS. 48(A) and 48(B).
[0403] FIGS. 48(A) and 48(B) are views showing the construction of
a magnification varying optical unit for the variable magnification
optical system of the fifth embodiment. The dot-dashed line shown
in each of FIGS. 48(A) and 48(B) represents the reference axis, and
the dot-dashed line shown in FIG. 48(A) shows the optical path of
an object ray passing through the center of the angle of view,
while the dot-dashed line shown in FIG. 48(B) shows the optical
path of a pupil ray (principal ray). FIGS. 48(A) and 48(B) show the
arrangement in which ray-folding plane reflecting surfaces 61 and
62 are respectively inserted between the reflecting surfaces 52 and
54 and between the reflecting surfaces 54 and 56 in the arrangement
of FIGS. 47(A) and 47(B), and the power arrangement of FIGS. 48(A)
and 48(B) is identical to that shown in FIGS. 47(A) and 47(B),
i.e., the curvature of each of the reflecting surfaces and the
angle of incidence of the reference axis on each of the reflecting
surfaces are the same as those of FIGS. 47(A) and 47(B). Letting
.phi..sub.61 and .phi..sub.62 are the respective angles of
incidence of the reference axis on the ray-folding plane reflecting
surfaces 61 and 62, if the following relation is satisfied:
3.theta.=.phi..sub.61+.phi..sub.62,
[0404] the entering reference axis and the exiting reference axis
of the magnification varying optical unit can be made to differ
from each other by 180.degree. in direction. Accordingly, the
above-described arrangement can be applied to the second optical
unit 14 shown in FIG. 44.
[0405] Similarly, if the arrangement shown in FIG. 48(A) is
reversed so that a light beam travels from the pupil plane 57 to
the object plane 51, this arrangement can be applied to another
magnification varying optical unit, i.e., the third optical unit 15
shown in FIG. 44.
[0406] Incidentally, it is preferable that each of the concave
reflecting surfaces (52, 54 and 56 in FIGS. 48(A) and 48(B)) of the
magnification varying optical unit be formed in such a manner that
the radius of curvature R.sub.y in a plane in which the reference
axis is bent (on the surface of the sheet of FIGS. 48(A) and 48(B),
i.e., in the Y, Z plane) is made different from the radius of
curvature R.sub.x in a plane which is perpendicular to the Y, Z
plane and contains a normal to a reference point of the concave
reflecting surface. Letting .theta. be the angle of incidence of
the reference axis on each of the concave reflecting surfaces, it
is necessary to satisfy the aforesaid equation 28 so that the focal
lengths in these two planes can be made coincident at the concave
reflecting surface.
[0407] FIG. 49 is a view showing the arrangement of the fifth
embodiment of the variable magnification optical system according
to the present invention. The arrangement shown in FIG. 49 includes
concave reflecting surfaces 71, 73, 75, 76, 78 and 80, and
ray-folding reflecting surfaces 72, 74, 77 and 79, and the
reflecting surfaces 71 to 75 constitute the second optical unit 14
and the reflecting surfaces 76 to 80 constitute the third optical
unit 15. The second and third optical units 14 and 15 serve as
magnification varying optical units, and the focal length f of each
of the second and third optical units 14 and 15 is negative. In
each of the magnification varying optical units 14 and 15, an
on-axial light beam forms an intermediate image once.
[0408] In the present invention, letting f.sub.i be the focal
length of the i-th magnification varying optical unit and letting k
be the number of times by which a parallel on-axial light beam
which has entered the i-th magnification varying optical unit forms
an intermediate image in the i-th magnification varying optical
unit, the magnification varying optical unit satisfies the
following condition:
f.sub.i.multidot.(-1).sup.k>0 (k is an integer not less than 0).
(Condition 2)
[0409] If the magnification varying optical unit satisfies
Condition 2, an image can be relayed from one reflecting surface to
another as intermediate images compactly folded by the reflecting
surfaces, so that a thin magnification varying portion can be
realized.
[0410] In the fifth embodiment, the magnification varying portion
is formed by a combination of two optical units consisting of three
concave reflecting surfaces having aspherical shapes and two
ray-folding reflecting surfaces. In this arrangement, the second
optical unit 14 and the third optical unit 15 in the arrangement of
FIG. 44 are formed as optical units having the aforesaid
arrangement.
[0411] Incidentally, the distance between each of the image forming
plane 13 and the refracting surface 71, 72, 73, 74 and 75 is equal,
and the distance between each of the refracting surface 76, 77, 78,
79 and 80 and the final image forming plane 16 is equal. In other
words, letting D(i-1) be the distance between a reflecting surface
Ri and a reflecting surface adjacent to the reflecting surface Ri
on the object side thereof and letting Di be the distance between
the reflecting surface Ri and a reflecting surface adjacent to the
reflecting surface Ri on the image side thereof, the following
relation is obtained: 10 Di D ( i - 1 ) = 1. (Equation29)
[0412] Incidentally, to fully correct off-axial aberration, it is
preferable that the refracting surfaces 71, 73, 75, 76, 78 and 80
be formed to have an asymmetrical shape in a plane in which the
reference axis is bent (the Y, Z plane).
[0413] In the arrangement shown in FIG. 49, a longer distance
between the reflecting surface 80 and the image forming plane 16
may be desired, i.e.., a longer back focus may be desired, in order
to dispose a glass member, such as a low-pass filter or an infrared
cut-filter, immediately in front of the final image forming plane
16. For this purpose, the state in which life-size image formation
is repeated by a plurality of times from the intermediate image
forming plane 13 to the final image forming plane 16 may be altered
as a whole, and the respective ray-folding reflecting surfaces 72,
74, 77 and 79 may be given appropriate curvatures so as to control
the entire power arrangement at each of the ray-folding reflecting
surfaces 72, 74, 77 and 79. Similarly to the concave reflecting
surfaces, if the reflecting surfaces 72, 74, 77 and 79 are formed
to have asymmetrical shapes in the plane in which the reference
axis is bent (the Y, Z plane), off-axial aberration can be
effectively corrected.
[0414] As described above, in the variable magnification optical
system of the fifth embodiment, the concave reflecting surfaces 71,
73, 75, 76, 78 and 80 shown in FIG. 49 are formed by aspheric
surfaces of rotational asymmetry, and the condition of movement of
the variable magnification optical system satisfies Condition 1
referred to above. The reflecting surfaces 71, 73, 75, 76, 78 and
80 are formed in such a manner that the radii of curvature R.sub.x
and R.sub.y of a paraxial region of each of the reflecting surfaces
71, 73, 75, 76, 78 and 80 slightly differ among the reflecting
surfaces on the basis of the condition of Equation 28,
specifically, within the following range: 11 .4 < ( R x R y 1
cos 2 ) < 2.5 . (Condition3)
[0415] In the variable magnification optical system according to
the present invention, a focal length variation due to an azimuth
must be corrected in the entire variable magnification optical
system over the entire range of variation of magnification. For
this purpose, it is preferable that such a focal length variation
be corrected in one optical unit as fully as possible and the
remaining non-corrected variation component be cancelled between
the magnification varying optical units.
[0416] Above or below the limits of Condition 3, the amount of
focal length variation due to an azimuth becomes large to such an
extent that the amount of correction becomes extremely insufficient
in each of the magnification varying optical units, with the result
that such a focal length variation is difficult to cancel between
the other magnification varying optical units over the entire range
of variation of magnification.
[0417] Incidentally, the focal length variation due to the azimuth
can be more effectively corrected by giving appropriate curvatures
to the respective ray-folding reflecting surfaces 72, 74, 77 and
79. If the ray-folding reflecting surfaces 72, 74, 77 and 79 are
formed by aspheric surfaces which are asymmetrical in the plane
which contains the entering and exiting reference axes, off-axial
aberration can be effectively corrected.
[0418] The aberrations may also be corrected by varying the
distance between each of the reflecting surfaces from Equation 29
and controlling the power arrangement. The distance between each of
the reflecting surfaces in the variable magnification optical
system according to the present invention is set within a range
which satisfies the following condition: 12 0.8 < ( Di D ( i - 1
) ) < 1.2 . (Condition4)
[0419] Above or below the limits of Condition 4, the image forming
action of a combined system consisting of adjacent two concave
reflecting surfaces (for example, 71 and 73) in the arrangement
shown in FIG. 49 is greatly deviated from life-size image formation
with respect to image formation or pupil formation, so that the
relation of cancellation of aberration between the two reflecting
surfaces is impaired and, particularly, off-axial aberration
becomes difficult to correct.
[0420] It is desirable that the three concave reflecting surfaces
of each of the magnification varying optical units shown in FIG. 49
have the radius of curvature, as described previously in connection
with FIGS. 47(A) and 47(B), but the power arrangement of the
magnification varying optical units may be controlled to correct
off-axial aberration. In the variable magnification optical system
according to the present invention, if each of the magnification
varying optical units contains a partial system which is formed by
a concave reflecting surface i, a reflecting surface (i+1), and a
concave reflecting surface (i+2) in that order, letting R.sub.y, i
and R.sub.y, i+2 be the radii of curvature of paraxial regions in a
plane which contains the entering and exiting reference axes at the
respective reference points of the concave reflecting surface i and
the concave reflecting surface (i+2), the radii of curvature
R.sub.y, i and R.sub.y, i+2 are set within a range which satisfies
the following condition: 13 0.5 < ( R y , i + 2 R y , i ) <
2.0 . (Condition5)
[0421] Above or below the limits of Condition 5, the image forming
action of a combined system consisting of adjacent two concave
reflecting surfaces (for example, 71 and 73) is greatly deviated
from life-size image formation with respect to image formation or
pupil formation, so that the relation of cancellation of aberration
between the two reflecting surfaces is impaired and, particularly,
off-axial aberration becomes difficult to correct.
[0422] In addition, if the lateral magnification of the
magnification varying portion composed of all the optical units is
set to approximately "1" at the wide-angle end, it is possible to
realize a variable magnification optical system which is kept thin
and corrected for aberration over the entire range of variation of
magnification. In the arrangement shown in FIG. 49, the size of the
final image forming plane 16 is kept constant during a
magnification varying operation, so that if the magnification
variation ratio is set to Z, the effective image size in the
intermediate image forming plane 13 at the wide-angle end becomes Z
times that obtainable at the telephoto end. Accordingly, the
respective effective sizes of the planes in the optical units 14
and 15 are basically determined at the wide-angle end. Accordingly,
it is preferable to set the lateral magnification of the entire
magnification varying portion to not greater than "1" at the
wide-angle end.
[0423] Basically, if image formation and pupil formation are to be
correctly relayed in each of the magnification varying optical
units, it is preferable to relay both of them through life-size
image formation. For this reason, it is desirable that the lateral
magnification of the magnification varying portion at the
wide-angle end be approximately "1". However, in the present
invention, in order to extend back focus, the power arrangement is
controlled by adjusting the life-size image formation within the
range represented by Conditions 3 to 5. The life-size image
formation is adjusted in such a way that a plurality of image
formations and pupil formations in the magnification varying
portion are varied within a range in which correction of aberration
is possible on the basis of the life-size image formation.
[0424] Accordingly, the lateral magnification of the entire
magnification varying portion which is determined by summing up
individual image formations or pupil formations deviated from the
life-size image formation is set to a value in a particular range
centered at "1". The lateral magnification at the wide-angle end of
the magnification varying portion of the variable magnification
optical system according to the present invention satisfies the
following condition:
0.5<.vertline..beta..sub.W.vertline.<1.5. (Condition 6)
[0425] Incidentally, the lateral magnification of a decentered
optical system can be calculated by using Equation 19. Strictly,
the lateral magnification .beta..sub.W is a paraxial value which is
calculated in the range of from a plane which is closest to the
object side in a magnification varying optical unit which is closet
to the object side to a plane which is closet to the image-plane
side in a magnification varying optical unit which is closest to
the image-plane side.
[0426] Incidentally, the aforesaid magnification varying optical
unit according to the present invention may be a surface mirror
whose medium is gas present among its reflecting surfaces, or a
transparent body on which a plurality of internal reflecting
surfaces are formed, i.e.., a transparent body which is composed of
a medium other than gas and internally reflects an entering ray.
FIG. 49 shows the former arrangement.
[0427] FIG. 50 shows another optical arrangement which adopts the
latter arrangement. Each optical element 801 and 802 is formed as a
transparent body made of glass, plastics or the like, and serves as
a magnification varying optical unit.
[0428] The optical element 801 includes a refracting surface 803
which is formed on the optical element 801 and allows a light beam
from the intermediate image forming plane 13 to enter the optical
element 801, internal reflecting surfaces 804, 805, 806, 807 and
808 each having a reflecting film formed on the surface of the
optical element 801, and a refracting surface 809 which allows the
light beam to exit from the optical element 801. The optical
element 802 includes a refracting surface 810 which is formed on
the optical element 802 and allows the light beam from the optical
element 801 to enter the optical element 802, internal reflecting
surfaces 811, 812, 813, 814 and 815 each having a reflecting film
formed on the surface of the optical element 802, and a refracting
surface 816 which allows the light beam to exit from the optical
element 802.
[0429] Each of the aforesaid reflecting surfaces is set in a way
which is basically identical to that described above in connection
with the reflecting surfaces shown in FIG. 49. However, if the
sizes of an intermediate image and a pupil formed in each of the
optical elements 801 and 802 are set equivalently to the
arrangement of FIG. 49 whose medium is air, the sizes in an actual
optical element become smaller according to the ratio of the
refractive index of the transparent body to the refractive index of
air. Accordingly, the arrangement of FIG. 50 can be made thin
compared to that of FIG. 49. In other words, in the arrangement of
FIG. 50, since the pupil size can be made larger for the same
thickness, the amount of light can be increased. Accordingly, if a
bright variable magnification optical system is needed, each of the
magnification varying optical units is preferably formed as a
transparent body on which two refracting surfaces and a plurality
of refracting surfaces are formed.
[0430] Incidentally, in each of the variable magnification optical
systems shown in FIGS. 49 and 50, focusing can be effected by
moving any one of the first to third optical units in the direction
of the reference axis. For example, an object which lies at a
closest distance can be focused by moving the first optical unit
toward an object side (toward the left as viewed in FIG. 49 or 50),
or by moving the second optical unit in a direction away from the
first optical unit (toward the right as viewed in FIG. 49 or 50),
or by moving the third optical unit in a direction away from the
second optical unit (toward the left as viewed in FIG. 49 or 50).
In particular, since the second and third optical units are
arranged to move in parallel with their respective entering
reference axes, if the second and third optical units are used as
focusing optical units, a magnification varying mechanism can be
used without modification for the purpose of focusing, so that the
required number of constituent components can be reduced. In such
arrangement, either or both of the second and third optical units
may be moved.
[0431] Incidentally, each of the optical elements 801 and 802 may
be prepared by cutting a transparent material into a shape having
the required refracting and reflecting surfaces, or by molding with
a mold having the inverse shape of the required refracting and
reflecting surfaces. If the optical elements 801 and 802 are
prepared by either method, the position accuracy of the surfaces is
higher than when each surface is independently formed, so that
adjustment of positions, inclinations or the like can be omitted.
In addition, since members for supporting the reflecting surfaces
are not needed, the required number of constituent components is
reduced.
[0432] In addition, holes or the like each of which receives a
guide bar for guiding the magnification varying movement of an
optical unit may be formed in predetermined transparent bodies in
the manner shown in FIG. 51. With this arrangement, since the
variable magnification optical system can be composed of such
transparent bodies alone, a member such as a barrel for holding
normal lenses is not needed, so that the required number of
constituent components can be reduced to a further extent.
[0433] Incidentally, if the required number of constituent
components is to be reduced, the first optical unit 12 shown in
each of FIGS. 49 and 50 may be basically any type of optical system
which forms an image on the intermediate image forming plane 13.
However, in order to realize a thin optical system which is one of
the objects of the present invention, it is necessary to dispose a
stop in front of the first optical unit 12. Otherwise, it is
necessary to dispose a stop at a position conjugate to the stop 11
so that an entrance pupil is formed in the vicinity of the first
surface.
[0434] If the first optical unit 12 is provided as a decentered
optical system, the decentering aberration remaining in a
magnification varying optical system can be cancelled by the first
optical unit 12, so that it is possible to realize an optical
system whose decentering aberration is reduced to a further extent.
In each of Numerical Examples 4 to 6 of the present invention which
will be described later, a particular optical element provided in
the first optical unit is formed of four or five decentered
reflecting surfaces so that decentering aberration can be fully
corrected over the entire variable magnification optical
system.
[0435] Prior to the detailed description of Numerical Examples 4 to
6, reference will be made to terms which are herein used to express
various constituent elements of the numerical examples, and matters
common to all the numerical examples.
[0436] FIG. 52 is an explanatory view of a coordinate system which
defines the constituent data of an optical system according to the
present invention. In each of the numerical examples 4 to 6 of the
present invention, the i-th surface is a surface which lies at the
i-th position numbered from an object side from which a ray travels
toward an image plane (the ray is shown by dot-dashed lines in FIG.
52 and is hereinafter referred to as the reference axis ray).
[0437] In FIG. 52, the first surface R1 is a stop, the second
surface R2 is a refracting surface coaxial with the first surface
R1, the third surface R3 is a reflecting surface which is tilted
with respect to the second surface R2, the fourth surface R4 is a
reflecting surface which is shifted and tilted with respect to the
third surface R3, the fifth surface R5 is a reflecting surface
which is shifted and tilted with respect to the fourth surface R4,
and the sixth surface R6 is a refracting surface which is shifted
and tilted with respect to the fifth surface R5. All of the second
surface R2 to the sixth surface R6 are arranged on one optical
element composed of a medium such as glass or plastics. In FIG. 52,
such optical element is shown as the first optical element B1.
[0438] Accordingly, in the arrangement shown in FIG. 52, the medium
between an object plane (not shown) and the second surface R2 is
air, the second surface R2 to the sixth surface R6 are arranged on
a certain common medium, and the medium between the sixth surface
R6 and the seventh surface R7 (not shown) is air.
[0439] Since the optical system according to the present invention
is an off-axial optical system, the surfaces which constitute part
of the optical system do not have a common optical axis. For this
reason, in each of the numerical examples of the present invention,
an absolute coordinate system is set, the origin of which is the
central point of an effective ray diameter at the first surface
which is the stop. In the present invention, each axis of the
absolute coordinate system is defined as follows:
[0440] Z axis: reference axis which passes through the origin and
extends to the second surface R2;
[0441] Y axis: straight line which passes through the origin and
makes an angle of 90.degree. with the z axis in the
counterclockwise direction in a tilting plane (on the surface of
the sheet of FIG. 52); and
[0442] X axis: straight line which passes through the origin and is
perpendicular to each of the Z and Y axes (perpendicular to the
surface of the sheet of FIG. 52).
[0443] If the surface shape of the i-th surface which constitutes
part of the optical system is to be expressed, it is possible to
more readily understand and recognize such surface shape by setting
a local coordinate system the origin of which is a point at which
the reference axis intersects with the i-th surface, and expressing
the surface shape of the i-th surface by using the local coordinate
system than by expressing the surface shape of the i-th surface by
using the absolute coordinate system. Accordingly, in the numerical
examples of the present invention the constituent data of which are
shown herein, the surface shape of the i-th surface is expressed by
its local coordinate system.
[0444] The tilting angle of the i-th surface in the Y, Z plane is
expressed by an angle .theta.i (unit: degree) which shows a
positive value in the counterclockwise direction with respect to
the Z axis of the absolute coordinate system. Accordingly, in each
of the numerical examples of the present invention, the origins of
the local coordinate systems of the respective surfaces are located
on the Y, Z plane, as shown in FIG. 52. The tilting or shifting of
the surfaces is absent in the X-Z plane or the X-Y plane. In
addition, the y and z axes of the local coordinates (x, y, z) of
the i-th surface are inclined by the angle .theta.i in the Y, Z
plane with respect to the absolute coordinate system (X, Y, Z).
Specifically, the x, y and z axes of the local coordinates (x, y,
z) are set in the follow manner:
[0445] z axis: straight line which passes through the origin of the
local coordinates and makes the angle .theta.i with the Z direction
of the absolute coordinate system in the counterclockwise direction
in the Y, Z plane;
[0446] y axis: straight line which passes through the origin of the
local coordinates and makes an angle of 90.degree. with the z
direction of the local coordinates in the counterclockwise
direction in the Y, Z plane; and
[0447] x axis: straight line which passes through the origin of the
local coordinates and is perpendicular to the Y, Z plane.
[0448] Symbol Di indicates a scalar which represents the distance
between the origin of the local coordinates of the i-th surface and
that of the (i+1)-st surface. Symbols Ndi and .upsilon.di
respectively indicate the refractive index and the Abbe number of
the medium between the i-th surface and the (i+1)-st surface. In
FIG. 52, each of the stop and the final image forming plane is
shown as one plane surface.
[0449] The optical system of each of the numerical examples of the
present invention varies its entire focal length (magnification) by
the movement of a plurality of optical elements. Regarding each of
the numerical examples which have the numerical data shown herein,
the cross section of its optical system and the numerical data are
shown with respect to three positions, i.e.., the wide-angle end
(W), the telephoto end (T) and the middle position (M).
[0450] If the optical element shown in FIG. 52 moves in the Y, Z
plane, the origin (Yi, Zi) of each of the local coordinate systems
which represent the positions of the respective surfaces takes on a
different value for each varied magnification position. However, in
the case of the numerical examples shown herein, since the optical
element is assumed to move in only the Z direction for the purpose
of variation of magnification, the coordinate value Zi is expressed
by Zi(W), Zi(M) and Zi(T) in the order of the wide-angle end, the
middle position and the telephoto end which respectively correspond
to three states to be taken by the optical system.
[0451] Incidentally, the coordinate values of each of the surfaces
represent those obtained at the wide-angle end, and each of the
middle position and the telephoto end is expressed as a difference
between the coordinate values obtained at the wide-angle end and
the coordinate values obtained at the respective one of the middle
position and the telephoto end. Specifically, letting "a" and "b"
be the respective amounts of movements of the optical element at
the middle position (M) and the telephoto end (T) with respect to
the wide-angle end (W), these amounts of movements are expressed by
the following equations:
Zi(M)=Zi(W)+a,
Zi(T)=Zi(W)+b.
[0452] If all the surfaces move in their Z plus directions, the
signs of "a" and "b" are positive, whereas if they move in their Z
minus directions, the signs of "a" and "b" are negative. The
surface-to-surface distance Di which varies with these movements is
a variable, and the values of the variable at the respective varied
magnification positions are collectively shown on tables which will
be referred to later.
[0453] Each of the numerical examples 4 to 6 of the present
invention has spheric surfaces and aspheric surfaces of rotational
asymmetry. Each of the spheric surfaces has a spherical shape
expressed by the radius of curvature R.sub.i. The sign of the
radius of curvature R.sub.i is plus if the center of curvature is
located in the z-axis plus direction of the local coordinates,
whereas if the center of curvature is located in the z-axis minus
direction of the local coordinates, the sign of the radius of
curvature R.sub.i is minus.
[0454] Each of the spheric surfaces is a shape expressed by the
following equation: 14 z = ( x 2 + y 2 ) / R i 1 + { 1 - ( x 2 + y
2 ) / R i 2 } 1 / 2 .
[0455] In addition, the optical system according to the present
invention has at least one aspheric surface of rotational
asymmetry, and its shape is expressed by the following equation in
which all the terms that contain the variable x having an odd
exponent are omitted from Equation 1 and such binomial coefficient
is put in the coefficient term of each of the remaining terms of
Equation 1:
z=C.sub.02y.sup.2+C.sub.20x.sup.2+C.sub.03y.sup.3+C.sub.21x.sup.2y+C.sub.0-
4y.sup.4+C.sub.22x.sup.2y.sup.2+C.sub.40x.sup.4.
[0456] Since the above curved-surface equation has only
even-exponent terms regarding x, the curved surface expressed by
the above curved-surface equation has a shape symmetrical with
respect to the Y, Z plane. Further, if the following condition is
satisfied, a shape symmetrical with respect to the X-Z plane is
obtained:
C.sub.03=C.sub.21=0.
[0457] Further, if the following equations are satisfied, a shape
of rotational symmetry is obtained:
C.sub.02=C.sub.20, C.sub.04=C.sub.40=C.sub.22/2.
[0458] If the above conditions are not satisfied, a shape of
rotational asymmetry is obtained.
[0459] The horizontal half-angle of view u.sub.Y is the maximum
angle of view of a light beam incident on the first surface R1 in
the Y, Z plane of FIG. 52, while the vertical half-angle of view
u.sub.X is the maximum angle of view of a light beam incident on
the first surface R1 in the X, Z plane of FIG. 52.
[0460] The brightness of the optical system is represented by an
entrance pupil diameter which is the diameter of an entrance pupil.
The effective image area in the image plane is represented by an
image size. The image size is represented by a rectangular region
having a horizontal size taken in the y direction of the local
coordinate system and a vertical size taken in the x direction of
the local coordinate system.
[0461] Regarding the numerical examples which are illustrated
together with the constituent data, their respective lateral
aberration charts are shown. Each of the lateral aberration charts
shows the lateral aberrations of a light beam for the wide-angle
end (W), the middle position (M) and the telephoto end (T), and the
lateral aberrations are those of the light beam which is incident
on the stop R1 at an angle of incidence which is defined by a
horizontal angle of incidence and a vertical angle of incidence
which are (u.sub.Y, u.sub.X), (0, u.sub.X), (-u.sub.Y, u.sub.X),
(u.sub.Y, 0), (0, 0) and (-u.sub.Y, 0), respectively. In each of
the lateral aberration charts, the horizontal axis represents the
height of incidence on the pupil, and the vertical axis represents
the amount of aberration. In any of the numerical examples, since
each of the surfaces basically has a shape symmetrical with respect
to the Y, Z plane, the plus and minus directions of a vertical
angle of view are the same in the lateral aberration chart. For
this reason, the lateral aberration chart relative to the minus
direction is omitted for the sake of simplicity.
[0462] The numerical examples 4 to 6 are described below.
[0463] [Numerical Example 4]
[0464] FIGS. 53, 54 and 55 are optical cross-sectional views taken
in the Y, Z plane, showing Numerical Example 4 relative to the
wide-angle end (W), the middle position (M) the telephoto end (T).
Numerical Example 4 is a variable magnification optical system
having a magnification variation ratio of approximately 3.times..
Constituent data for Numerical Example 4 are shown below.
9 WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END HORIZONTAL
HALF-ANGLE 27.3 19.0 9.8 OF VIEW VERTICAL HALF-ANGLE 21.2 14.5 7.4
OF VIEW APERTURE DIAMETER 1.30 1.40 2.40 IMAGE SIZE 3.76 .times.
2.82 mm i Yi Zi(W) .theta.i Di Ndi .nu.di FIRST OPTICAL ELEMENT B1
(NEGATIVE LENS) 1 0.00 0.00 0.00 0.66 1.51633 64.15 REFRACTING
SURFACE 2 0.00 0.66 0.00 2.00 1 REFRACTING SURFACE 3 0.00 2.66 0.00
1.00 1 STOP SECOND OPTICAL ELEMENT B2 4 0.00 3.66 0.00 6.00 1.49171
57.40 REFRACTING SURFACE 5 0.00 9.66 30.00 7.40 1.49171 57.40
REFLECTING SURFACE 6 -6.41 5.96 30.00 7.00 1.49171 57.40 REFLECTING
SURFACE 7 -6.41 12.96 30.00 7.40 1.49171 57.40 REFLECTING SURFACE 8
-12.82 9.26 30.00 10.00 1.49171 57.40 REFLECTING SURFACE 9 -12.82
19.26 0.00 VARIABLE 1 REFRACTING SURFACE THIRD OPTICAL ELEMENT B3
10 -12.82 23.32 0.00 5.00 1.49171 57.40 REFRACTING SURFACE 11
-12.82 28.32 -30.00 8.00 1.49171 57.40 REFLECTING SURFACE 12 -5.89
24.32 -15.00 8.00 1.49171 57.40 REFLECTING SURFACE 13 -1.89 31.25
0.00 8.00 1.49171 57.40 REFLECTING SURFACE 14 2.11 24.32 15.00 8.00
1.49171 57.40 REFLECTING SURFACE 15 9.04 28.32 30.00 6.00 1.49171
57.40 REFLECTING SURFACE 16 9.04 22.32 0.00 VARIABLE 1 REFRACTING
SURFACE FOURTH OPTICAL ELEMENT B4 17 9.04 19.92 0.00 6.00 1.49171
57.40 REFRACTING SURFACE 18 9.04 13.92 30.00 8.00 1.49171 57.40
REFLECTING SURFACE 19 15.97 17.92 15.00 8.00 1.49171 57.40
REFLECTING SURFACE 20 19.97 11.00 0.00 8.00 1.49171 57.40
REFLECTING SURFACE 21 23.97 17.92 -15.00 8.00 1.49171 57.40
REFLECTING SURFACE 22 30.90 13.92 -30.00 6.00 1.49171 57.40
REFLECTING SURFACE 23 30.90 19.92 0.00 VARIABLE 1 REFRACTING
SURFACE 24 30.90 21.65 0.00 2.08 1.51400 70.00 FILTER 25 30.90
23.73 0.00 0.00 1 26 30.90 23.73 0.00 1.60 1.52000 74.00 FILTER 27
30.90 25.33 0.00 1.00 1 28 30.90 26.33 0.00 0.80 1.51633 64.15
COVER GLASS 29 30.90 27.13 0.00 0.91 1 30 30.90 28.04 0.00 IMAGE
PLANE WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END D9 4.06 2.54
0.60 D16 2.40 2.72 5.34 D23 1.72 3.57 8.12 R1-R9 Zi(M) = Zi(W)
Zi(T) = Zi(W) R10-R16 Zi(M) = Zi(W) - 1.53 Zi(T) = Zi(W) - 3.46
R17-R23 Zi(M) = Zi(W) - 1.84 Zi(T) = Zi(W) - 6.40 R24-R30 Zi(M) =
Zi(W) Zi(T) = Zi(W) SPHERICAL SHAPE R1 R.sub.1 = 6.168 R2 R.sub.2 =
3.604 R4 R.sub.4 = 8.000 R9 R.sub.9 = -8.094 R10 R.sub.10 = -14.301
R16 R.sub.16 = -14.930 R17 R.sub.17 = 7.534 R23 R.sub.23 = .infin.
R24 R.sub.24 = .infin. R25 R.sub.25 = .infin. R26 R.sub.26 =
.infin. R27 R.sub.27 = .infin. R28 R.sub.28 = .infin. R29 R.sub.29
= .infin. ASPHERICAL SHAPE R5 C.sub.02 = -2.48795e-02 C.sub.20 =
-6.93059e-02 C.sub.03 = 5.73301e-04 C.sub.21 = -1.68160e-03
C.sub.04 = 9.86673e-05 C.sub.22 = -2.62542e-04 C.sub.40 =
-4.65288e-04 R6 C.sub.02 = 2.57868e-02 C.sub.20 = 4.25914e-02
C.sub.03 = -1.22602e-03 C.sub.21 = 4.81265e-03 C.sub.04 =
2.82052e-05 C.sub.22 = -4.29430e-04 C.sub.40 = -3.48277e-04 R7
C.sub.02 = -3.32169e-02 C.sub.20 = -2.79739e-02 C.sub.03 =
1.26172e-04 C.sub.21 = -4.74552e-03 C.sub.04 = -6.48835e-06
C.sub.22 = 3.07151e-04 C.sub.40 = -2.51179e-04 R8 C.sub.02 =
5.18661e-02 C.sub.20 = 3.05881e-02 C.sub.03 = -7.39583e-04 C.sub.21
= 1.89622e-03 C.sub.04 = 3.23835e-04 C.sub.22 = 2.51407e-04
C.sub.40 = -2.30108e-05 R11 C.sub.02 = -3.36682e-02 C.sub.20 =
-4.23355e-02 C.sub.03 = -3.58878e-05 C.sub.21 = -1.31841e-03
C.sub.04 = -4.76471e-05 C.sub.22 = 1.22212e-06 C.sub.40 =
-1.38018e-04 R12 C.sub.02 = -8.45125e-03 C.sub.20 = -2.53367e-03
C.sub.03 = -1.24138e-03 C.sub.21 = 2.73698e-03 C.sub.04 =
-2.30027e-04 C.sub.22 = 3.34562e-04 C.sub.40 = -2.12308e-04 R13
C.sub.02 = -2.14116e-02 C.sub.20 = -4.05649e-02 C.sub.03 =
7.57771e-04 C.sub.21 = -2.94840e-03 C.sub.04 = -1.10645e-04
C.sub.22 = 4.30439e-05 C.sub.40 = -1.13097e-04 R14 C.sub.02 =
-3.32218e-03 C.sub.20 = -4.16062e-02 C.sub.03 = -1.88788e-04
C.sub.21 = 1.23956e-02 C.sub.04 = 1.17299e-05 C.sub.22 =
8.52794e-04 C.sub.40 = 7.74804e-04 R15 C.sub.02 = -2.41680e-02
C.sub.20 = -4.37423e-02 C.sub.03 = -5.81282e-05 C.sub.21 =
-4.16500e-04 C.sub.04 = -3.44370e-05 C.sub.22 = -1.41119e-04
C.sub.40 = -9.40307e-05 R18 C.sub.02 = 2.51483-02 C.sub.20 =
1.51580e-02 C.sub.03 = -4.43147e-04 C.sub.21 = 1.98560e-03 C.sub.04
= -2.88674e-05 C.sub.22 = -4.64797e-04 C.sub.40 = -2.21638e-04 R19
C.sub.02 = 1.595911e-02 C.sub.20 = 1.99007e-02 C.sub.03 =
2.33671e-04 C.sub.21 = -3.88447e-03 C.sub.04 = 1.42672e-04 C.sub.22
= -1.24441e-03 C.sub.40 = -2.62688e-04 R20 C.sub.02 = 3.09393e-02
C.sub.20 = 4.11529e-02 C.sub.03 = -1.45588e-04 C.sub.21 =
3.72684e-04 C.sub.04 = 5.42962e-05 C.sub.22 = 3.92704e-05 C.sub.40
= 7.42443e-05 R21 C.sub.02 = 2.01137e-02 C.sub.20 = 7.57535e-02
C.sub.03 = 1.37833e-04 C.sub.21 = -8.04032e-03 C.sub.04 =
1.60523e-04 C.sub.22 = -1.16036e-04 C.sub.40 = 1.84743e-03 R22
C.sub.02 = 1.94558e-02 C.sub.20 = 3.42531e-02 C.sub.03 =
-3.77644e-04 C.sub.21 = -1.04434e-03 C.sub.04 = 2.05664e-05
C.sub.22 = 6.08001e-05 C.sub.40 = 9.48100e-05
[0465] The construction of Numerical Example 4 will be described
below. The first optical element B1 is a negative lens which has
the first surface R1 and the second surface R2, and the third
surface R3 is an aperture plane. The second optical element B2 is
formed as one transparent body on which the fourth surface R4
(entrance refracting surface), the fifth to eighth surfaces R5 to
R8 each of which is a decentered curved internal reflecting
surface, and the ninth surface R9 (exit refracting surface) are
formed. The third optical element B3 is formed as one transparent
body on which the tenth surface R10 (entrance refracting surface),
the eleventh to fifteenth surfaces R11 to R15 each of which is a
decentered curved internal reflecting surface, and the sixteenth
surface R16 (exit refracting surface) are formed. The fourth
optical element B4 is formed as one transparent body on which the
seventeenth surface R17 (entrance refracting surface), the
eighteenth to twenty-second surfaces R18 to R22 each of which is a
decentered curved internal reflecting surface, and the twenty-third
surface R23 (exit refracting surface) are formed.
[0466] The twenty-fourth to twenty-ninth surfaces R24 to R29 are
those of plane parallel plates such as a filter and a cover glass.
The thirtieth surface R30 is a final image plane in which the image
pickup surface of an image pickup device such as a CCD is
positioned.
[0467] The optical elements of Numerical Example 4 are grouped into
three optical units which constitute a variable magnification
optical system. Specifically, the first optical element B1, the
stop R3 and the second optical element B2 constitute the first
optical unit, the third optical element B3 constitutes the second
optical unit, and the fourth optical element B4 constitutes the
third optical unit. The second and third optical units are
magnification varying optical units which vary the relative
position therebetween to vary the magnification of the variable
magnification optical system. The concave reflecting surfaces R11,
R13, R15, R18, R20 and R22 effectively act to relay the aforesaid
intermediate images and pupil images in each of the magnification
varying optical units.
[0468] An image forming operation for an object lying at infinity
will be described below. First, a light beam which has passed
through the first optical element B1 and the stop R3 in that order
enters the second optical element B2. In the second optical element
B2, the light beam is refracted by the fourth surface R4, then
reflected from surface to surface by the fifth surface R5 to the
eighth surface R8, then refracted by the ninth surface R9, and then
exits from the second optical element B2. During this time, a
primary image is formed in the vicinity of the sixth surface R6,
and a secondary image is formed between the eighth surface R8 and
the ninth surface R9. A pupil is formed between the seventh surface
R7 and the eighth surface R8.
[0469] Then, the light beam enters the third optical element B3. In
the third optical element B3, the light beam is refracted by the
tenth surface R10, then reflected from surface to surface by the
eleventh surface R11 to the fifteenth surface R15, then refracted
by the sixteenth surface R16, and then exits from the third optical
element B3. During this time, a tertiary image forming plane is
formed between the twelfth surface R12 and the thirteenth surface
R13 when the focal length is at the wide-angle end, or in the
vicinity of the thirteenth surface R13 when the focal length is at
the telephoto end. Another pupil is formed between the fourteenth
surface R14 and the fifteenth surface R15 when the focal length is
at the wide-angle end, or in the vicinity of the sixteenth surface
R16 when the focal length is at the telephoto end.
[0470] Then, the light beam enters the fourth optical element B4.
In the fourth optical element B4, the light beam is refracted by
the seventeenth surface R17, then reflected from surface to surface
by the eighteenth surface R18 to the twenty-second surface R22,
then refracted by the twenty-third surface R23, and then exits from
the fourth optical element B4. During this time, a quaternary image
forming plane is formed between the eighteenth surface R18 and the
nineteenth surface R19 when the focal length is at the wide-angle
end, or in the vicinity of the nineteenth surface R19 when the
focal length is at the telephoto end. A pupil is formed in the
vicinity of the twenty-second surface R22 when the focal length is
at the wide-angle end, or between the twenty-second surface R22 and
the twenty-third surface R23 when the focal length is at the
telephoto end.
[0471] The light beam which has exited from the fourth optical
element B4 passes through the twenty-fourth to twenty-ninth
surfaces R24 to R29, and finally forms an object image on the
thirtieth surface R30 which is a quinary image forming plane.
[0472] In Numerical Example 4, the entering reference axis and the
exiting reference axis of each of the second optical element B2 are
the same as each other in direction. The entering reference axis
and the exiting reference axis of each of the third optical element
B3 and the fourth optical element B4 differ from each other by
180.degree. in direction.
[0473] The movements of the respective optical elements during a
magnification varying operation will be described below. During the
magnification varying operation, the first optical element B1, the
stop R3 and the second optical element B2 which constitute the
first optical unit are fixed and do not move. As the focal length
varies from the wide-angle end toward the telephoto end, the third
optical element B3 moves in the Z minus direction in parallel with
the entering reference axis of the third optical element B3. In the
meantime, the fourth optical element B4 moves in the Z minus
direction in parallel with the entering reference axis of the
fourth optical element B4.
[0474] During the magnification varying operation, the filter, the
cover glass and the thirtieth surface R30 which is the final image
plane do not move. In the present specification, these plane
parallel plates, which do not have refractive power, are not
regarded as optical units which constitute part of the optical
system.
[0475] As the focal length varies from the wide-angle end toward
the telephoto end, the distance between the second optical element
B2 and the third optical element B3 is decreased, the distance
between the third optical element B3 and the fourth optical element
B4 is increased, and the distance between the fourth optical
element B4 and the twenty-fourth surface R24 is increased.
[0476] In addition, as the focal length varies from the wide-angle
end toward the telephoto end, the entire optical path length which
extends from the first surface R1 to the final image plane R30
becomes longer.
[0477] Each of FIGS. 56, 57 and 58 shows lateral aberration charts
of Numerical Example 4 relative to the wide-angle end (W), the
middle position (M) and the telephoto end (T). The respective
lateral aberration charts show lateral aberrations in the Y and X
directions, relative to six light beams which enter Numerical
Example 4 at different angles of incidence of (u.sub.Y, u.sub.X),
(0, u.sub.X), (-u.sub.Y, u.sub.X), (u.sub.Y, 0), (0, 0) and
(-u.sub.Y, 0), respectively. The horizontal axis of each of the
lateral aberration charts represents the height of incidence in the
Y or X direction of a light beam which is incident on each of the
entrance pupils.
[0478] As can be seen from these figures, Numerical Example 4 is
capable of achieving well-balanced correction of aberration at each
zoom position.
[0479] In addition, the optical system of Numerical Example 4 is
approximately 7.6 mm thick for an image size of 3.76 mm.times.2.82
mm. In Numerical Example 4, particularly because each of the
optical elements and the entire optical system has a small
thickness and each of the optical elements can be constructed by
forming reflecting surfaces on predetermined sides of a
plate-shaped transparent body, it is possible to readily construct
a variable magnification optical system which is thin as a whole,
by adopting a mechanism which causes two optical elements to move
along a surface of one base plate.
[0480] Incidentally, in Numerical Example 4, although a chromatic
aberration is caused by a plurality of refracting surfaces, the
curvature of each of the refracting surfaces is appropriately
determined so that the chromatic aberration is corrected over the
entire magnification variation range. In particular, an axial
chromatic aberration which occurs at the fourth surface R4 is fully
corrected by the negative lens disposed immediately in front of the
stop.
[0481] Numerical Example 4 is the variable magnification optical
system in which the negative lens is provided on the object side of
the stop of the fifth embodiment shown in FIG. 50.
[0482] [Numerical Example 5]
[0483] FIGS. 59, 60 and 61 are optical cross-sectional views taken
in the Y, Z plane, showing Numerical Example 5 relative to the
wide-angle end (W), the middle position (M) and the telephoto end
(T). Numerical Example 5 is a variable magnification optical system
having a magnification variation ratio of approximately 3.times..
Constituent data for Numerical Example 5 are shown below.
10 WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END HORIZONTAL
HALF-ANGLE 26.0 18.0 9.2 OF VIEW VERTICAL HALF-ANGLE 20.0 13.6 6.9
OF VIEW APERTURE DIAMETER 1.40 2.00 2.80 IMAGE SIZE 4.8 .times. 3.6
mm i Yi Zi(W) .theta.i Di Ndi .nu.di FIRST OPTICAL ELEMENT B1
(NEGATIVE LENS) 1 0.00 0.00 0.00 1.00 1.49700 81.61 REFRACTING
SURFACE 2 0.00 1.00 0.00 3.00 1 REFRACTING SURFACE 3 0.00 4.00 0.00
2.00 1 STOP SECOND OPTICAL ELEMENT B2 4 0.00 6.00 0.00 13.00
1.58312 59.37 REFRACTING SURFACE 5 0.00 19.00 34.00 9.00 1.58312
59.37 REFLECTING SURFACE 6 -8.34 15.63 19.00 9.00 1.58312 59.37
REFLECTING SURFACE 7 -12.84 23.42 0.00 9.00 1.58312 59.37
REFLECTING SURFACE 8 -17.34 15.63 -15.00 9.00 1.58312 59.37
REFLECTING SURFACE 9 -25.14 20.13 -30.00 12.00 1.58312 59.37
REFLECTING SURFACE 10 -25.14 8.13 0.00 0.00 1 REFRACTING SURFACE
THIRD OPTICAL ELEMENT B3 (POSITIVE LENS) 10' -25.14 8.13 0.00 2.00
1.76181 26.51 REFRACTING SURFACE 11 -25.14 6.13 0.00 VARIABLE 1
REFRACTING SURFACE FOURTH OPTICAL ELEMENT B4 12 -25.14 -1.01 0.00
7.00 1.58312 59.37 REFRACTING SURFACE 13 -25.14 -8.01 -32.00 10.00
1.58312 59.37 REFLECTING SURFACE 14 -34.13 -3.63 -16.00 10.00
1.58312 59.37 REFLECTING SURFACE 15 -39.43 -12.11 0.00 10.00
1.58312 59.37 REFLECTING SURFACE 16 -44.73 -3.63 16.00 10.00
1.58312 59.37 REFLECTING SURFACE 17 -53.71 -8.01 32.00 7.00 1.58312
59.37 REFLECTING SURFACE 18 -53.17 -1.01 0.00 VARIABLE 1 REFRACTING
SURFACE FIFTH OPTICAL ELEMENT B5 19 -53.71 3.78 0.00 8.00 1.58312
59.37 REFRACTING SURFACE 20 -53.71 11.78 30.00 10.00 1.58312 59.37
REFLECTING SURFACE 21 -62.37 6.78 15.00 10.00 1.58312 59.37
REFLECTING SURFACE 22 -67.37 15.44 0.00 10.00 1.58312 59.37
REFLECTING SURFACE 23 -72.37 6.78 -15.00 10.00 1.58312 59.37
REFLECTING SURFACE 24 -81.03 11.78 -30.00 7.00 1.58312 59.37
REFLECTING SURFACE 25 -81.03 4.78 0.00 VARIABLE 1 REFRACTING
SURFACE 26 -81.03 3.44 0.00 1.80 1.51633 64.15 FILTER 27 -81.03
1.64 0.00 0.00 1 28 -81.03 1.64 0.00 2.20 1.51633 64.15 FILTER 29
-81.03 -0.56 0.00 9.00 1 30 -81.03 -9.56 0.00 0.80 1.51633 64.15
COVER GLASS 31 -81.03 -10.36 -0.00 1.00 1 32 -81.03 -11.36 FINAL
IMAGE FORMING PLANE WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END
D11 7.14 4.84 2.37 D18 4.79 4.67 8.64 D25 1.34 3.52 9.96 R1-R11
Zi(M) = Zi(W) Zi(T) = Zi(W) R12-R18 Zi(M) = Zi(W) + 2.30 Zi(T) =
Zi(W) + 4.77 R19-R25 Zi(M) = Zi(W) + 2.18 Zi(T) = Zi(W) + 8.61
R26-R32 Zi(M) = Zi(W) Zi(T) = Zi(W) SPHERICAL SHAPE R1 R.sub.1 =
.infin. R2 R.sub.2 = 10.000 R4 R.sub.4 = 10.000 R10 R.sub.10 =
-8.400 R11 R.sub.11 = 43.931 R12 R.sub.12 = 10.000 R18 R.sub.18 =
10.577 R19 R.sub.19 = .infin. R25 R.sub.25 = .infin. R26 R.sub.26 =
.infin. R27 R.sub.27 = .infin. R28 R.sub.28 = .infin. R29 R.sub.29
= .infin. R30 R.sub.30 = .infin. ASPHERICAL SHAPE R5 C.sub.02 =
-2.72936e-02 C.sub.20 = -3.34457e-02 C.sub.03 = 2.09387e-04
C.sub.21 = 1.09608e-04 C.sub.04 = 3.65695e-05 C.sub.22 =
-8.82752e-05 C.sub.40 = -2.30222e-07 R6 C.sub.02 = 3.44322e-05
C.sub.20 = -3.97258e-02 C.sub.03 = -1.24585e-03 C.sub.21 =
-7.55604e-03 C.sub.04 = -2.57973e-04 C.sub.22 = -8.79636e-04
C.sub.40 = 1.91328e-03 R7 C.sub.02 = -2.70082e-02 C.sub.20 =
-4.40194e-02 C.sub.03 = -6.33660e-05 C.sub.21 = 2.38734e-05
C.sub.04 = -1.64944e-05 C.sub.22 = -8.84975e-05 C.sub.40 =
-8.88770e-05 R8 C.sub.02 = -5.33009e-03 C.sub.20 = -4.59243e-02
C.sub.03 = 1.26419e-03 C.sub.21 = 5.93561e-03 C.sub.04 =
-7.16610e-05 C.sub.22 = -2.67759e-04 C.sub.40 = -1.44607e-04 R9
C.sub.02 = -1.87121e-02 C.sub.20 = -3.92180e-02 C.sub.03 =
4.37501e-04 C.sub.21 = 4.46436e-04 C.sub.04 = -4.98868e-05 C.sub.22
= -6.31610e-05 C.sub.40 = -5.60586e-05 R13 C.sub.02 = 2.34150e-02
C.sub.20 = 3.64057e-02 C.sub.03 = 1.02145e-04 C.sub.21 =
4.68498e-04 C.sub.04 = 2.92271e-05 C.sub.22 = 1.09843e-04 C.sub.40
= 6.77913e-05 R14 C.sub.02 = -6.97862e-04 C.sub.20 = 3.46717e-02
C.sub.03 = 1.79534e-04 C.sub.21 = 4.31674e-03 C.sub.04 =
3.30144e-04 C.sub.22 = 5.23135e-04 C.sub.40 = 7.90998e-04 R15
C.sub.02 = 1.60878e-02 C.sub.20 = 3.79592e-02 C.sub.03 =
2.34613e-04 C.sub.21 = -1.38600e-04 C.sub.04 = 4.98729e-06 C.sub.22
= -2.05181e-05 C.sub.40 = 1.89633e-05 R16 C.sub.02 = 3.52434e-03
C.sub.20 = 5.37197e-02 C.sub.03 = -4.89992e-05 C.sub.21 =
9.97199e-04 C.sub.04 = 2.31611e-05 C.sub.22 = 8.93152e-04 C.sub.40
= -7.89179e-04 R17 C.sub.02 = 1.99213e-02 C.sub.20 = 3.37854e-02
C.sub.03 = 3.28820e-05 C.sub.21 = -3.43089e-04 C.sub.04 =
6.26649e-06 C.sub.22 = 5.90309e-05 C.sub.40 = 2.48524e-05 R20
C.sub.02 = -1.63827e-02 C.sub.20 = -2.23970e-02 C.sub.03 =
2.88869e-04 C.sub.21 = 8.53595e-04 C.sub.04 = -1.85852e-06 C.sub.22
= -6.00163e-05 C.sub.40 = -9.69682e-05 R21 C.sub.02 = -1.52735e-02
C.sub.20 = -5.01525e-02 C.sub.03 = 6.27635e-04 C.sub.21 =
-7.57356e-03 C.sub.04 = 1.68568e-05 C.sub.22 = -5.09136e-04
C.sub.40 = -1.70684e-03 R22 C.sub.02 = -1.86688e-02 C.sub.20 =
-3.18271e-02 C.sub.03 = 6.79138e-05 C.sub.2 = -3.05799e-04 C.sub.04
= -2.00801e-05 C.sub.22 = -1.39814e-04 C.sub.40 = -6.11987e-05 R23
C.sub.02 = -1.26889e-02 C.sub.20 = -4.73700e-02 C.sub.03 =
-1.42598e-04 C.sub.21 = -1.34375e-03 C.sub.04 = -5.42168e-05
C.sub.22 = -3.13011e-04 C.sub.40 = -4.55329e-04 R24 C.sub.02 =
-1.65129e-02 C.sub.20 = -2.42770e-02 C.sub.03 = -9.19071e-05
C.sub.21 = 1.27830e-04 C.sub.04 = -9.52284e-06 C.sub.22 =
-5.03070e-05 C.sub.40 = -1.25140e-05
[0484] The construction of Numerical Example 5 will be described
below. The first optical element B1 is a negative lens which has
the first surface R1 and the second surface R2, and the third
surface R3 is an aperture plane. The second optical element B2 is
formed as one transparent body on which the fourth surface R4
(entrance refracting surface), the fifth to ninth surfaces R5 to R9
each of which is a decentered curved internal reflecting surface,
and the tenth surface R10 (exit refracting surface) are formed. The
third optical element B3 is a positive lens which has the
tenth-apostrophe surface R10 and the eleventh surface R11. The
second optical element B2 and the third optical element B3 are
joined to each other at the tenth-apostrophe surface R10' and the
tenth surface R10.
[0485] The fourth optical element B4 is formed as one transparent
body on which the twelfth surface R12 (entrance refracting
surface), the thirteenth to seventeenth surfaces R13 to R17 each of
which is a decentered curved internal reflecting surface, and the
eighteenth surface R18 (exit refracting surface) are formed. The
fifth optical element B5 is formed as one transparent body on which
the nineteenth surface R19 (entrance refracting surface), the
twentieth to twenty-fourth surfaces R20 to R24 each of which is a
decentered curved internal reflecting surface, and the twenty-fifth
surface R25 (exit refracting surface) are formed.
[0486] The twenty-sixth to thirty-first surfaces R26 to R31 are
those of plane parallel plates such as a filter and a cover glass.
The thirty-second surface R32 is a final image plane in which the
image pickup surface of an image pickup device such as a CCD is
positioned.
[0487] The optical elements of Numerical Example 5 are grouped into
three optical units which constitute a variable magnification
optical system. Specifically, the first optical element B1, the
stop R3, the second optical element B2 and the third optical
element B3 constitute the first optical unit, the fourth optical
element B4 constitutes the second optical unit, and the fifth
optical element B5 constitutes the third optical unit. The second
and fourth optical units are magnification varying optical units
which vary the relative position therebetween to vary the
magnification of the variable magnification optical system. The
concave reflecting surfaces R13, R15, R17, R20, R22 and R24
effectively act to relay the aforesaid intermediate images and
pupil images in each of the magnification varying optical
units.
[0488] An image forming operation for an object lying at infinity
will be described below. First, a light beam which has passed
through the first optical element B1 and the stop R3 in that order
enters the second optical element B2. In the second optical element
B2, the light beam is refracted by the fourth surface R4, then
reflected from surface to surface by the fifth surface R5 to the
ninth surface R9, then refracted by the tenth surface R10, and then
enters the third optical element B3. In the third optical element
B3, the light beam is refracted by the eleventh surface R11, and
then exits from the third optical element B3. During this time, a
primary image is formed in the vicinity of the sixth surface R6,
and a secondary image is formed between the ninth surface R9 and
the tenth surface R10. A pupil is formed between the sixth surface
R6 and the seventh surface R7.
[0489] Then, the light beam enters the fourth optical element B4.
In the fourth optical element B4, the light beam is refracted by
the twelfth surface R12, then reflected from surface to surface by
the thirteenth surface R13 to the seventeenth surface R17, then
refracted by the eighteenth surface R18, and then exits from the
fourth optical element B4. During this time, a tertiary image
forming plane is formed in the vicinity of the fifteenth surface
R15 when the focal length is at the wide-angle end, or between the
fifteenth surface R15 and the sixteenth surface R16 when the focal
length is at the telephoto end. A pupil is formed between the
sixteenth surface R16 and the seventeenth surface R17 when the
focal length is at the wide-angle end, or in the vicinity of the
eighteenth surface R18 when the focal length is at the telephoto
end.
[0490] Then, the light beam enters the fifth optical element B5. In
the fifth optical element B5, the light beam is refracted by the
nineteenth surface R19, then reflected from surface to surface by
the twentieth surface R20 to the twenty-fourth surface R24, then
refracted by the twenty-fifth surface R25, and then exits from the
fifth optical element B5. During this time, a quaternary image
forming plane is formed in the vicinity of the twenty-first surface
R21 when the focal length is at the wide-angle end, or between the
twenty-first surface R21 and the twenty-second surface R22 when the
focal length is at the telephoto end. A pupil is formed in the
vicinity of the twenty-fourth surface R24 when the focal length is
at the wide-angle end, or in the vicinity of the twenty-fifth
surface R25 when the focal length is at the telephoto end.
[0491] The light beam which has exited from the fifth optical
element B5 passes through the twenty-sixth to thirty-first surfaces
R26 to R31, and finally forms an object image on the thirty-second
surface R32 which is a quinary image forming plane.
[0492] In Numerical Example 5, the entering reference axis and the
exiting reference axis of each of the second optical element B2,
the fourth optical element B4 and the fifth optical element B5
differ from each other by 180.degree. in direction.
[0493] The movements of the respective optical elements during a
magnification varying operation will be described below. During the
magnification varying operation, the first optical element B1, the
stop R3, the second optical element B2 and the third optical
element B3 which constitute the first optical unit are fixed and do
not move. As the focal length varies from the wide-angle end toward
the telephoto end, the fourth optical element B4 moves in the Z
plus direction in parallel with the entering reference axis of the
fourth optical element B4. In the meantime, the fifth optical
element B5 moves in the Z plus direction in parallel with the
entering reference axis of the fifth optical element B5.
[0494] During the magnification varying operation, the filter, the
cover glass and the thirty-second surface R32 which is the final
image plane do not move.
[0495] Thus, as the focal length varies from the wide-angle end
toward the telephoto end, the distance between the third optical
element B3 and the fourth optical element B4 is decreased, the
distance between the fourth optical element B4 and the fifth
optical element B5 is temporarily decreased and then increased, and
the distance between the twenty-sixth surface R26 and the final
image plane R32 is increased.
[0496] In addition, as the focal length varies from the wide-angle
end toward the telephoto end, the entire optical path length which
extends from the first surface R1 to the final image plane R32
becomes temporarily shorter and then longer.
[0497] Each of FIGS. 62, 63 and 64 shows lateral aberration charts
of Numerical Example 5 relative to the wide-angle end (W), the
middle position (M) and the telephoto end (T). The respective
lateral aberration charts show lateral aberrations in the Y and X
directions, relative to six light beams which enter Numerical
Example 5 at different angles of incidence of (u.sub.Y, u.sub.X),
(0, u.sub.X), (-u.sub.Y, u.sub.X), (u.sub.Y, 0), (0, 0) and
(-u.sub.Y, 0), respectively. The horizontal axis of each of the
lateral aberration charts represents the height of incidence in the
Y or X direction of a light beam which is incident on each of the
entrance pupils.
[0498] As can be seen from these figures, Numerical Example 5 is
capable of achieving well-balanced correction of aberration at each
zoom position.
[0499] Incidentally, in Numerical Example 5, although a chromatic
aberration is caused by a plurality of refracting surfaces, the
curvature of each of the refracting surfaces is appropriately
determined so that the chromatic aberration is corrected over the
entire magnification variation range. In particular, an axial
chromatic aberration which occurs at the fourth surface R4 is fully
corrected by the concave lens disposed immediately in front of the
stop. Lateral chromatic aberration is fully corrected by securing a
lens having a different refractive index (third optical element B3)
to the second optical element B2.
[0500] In addition, the optical system of Numerical Example 5 is
approximately 10.0 mm thick for an image size of 4.8 mm.times.3.6
mm. In Numerical Example 5, particularly because each of the
optical elements and the entire optical system has a small
thickness and each of the optical elements can be constructed by
forming reflecting surfaces on predetermined sides of a
plate-shaped transparent body, it is possible to readily construct
a variable magnification optical system which is thin as a whole,
by adopting a mechanism which causes two optical elements to move
along a surface of one base plate.
[0501] Numerical Example 5 is the variable magnification optical
system in which, in the fifth embodiment shown in FIG. 50, the
first optical unit is formed as an optical unit having an entering
reference axis and an exiting reference axis which differ from each
other by 180.degree. in direction, and one negative lens is
provided on the object side of the stop.
[0502] Incidentally, all the reference axes of Numerical Example 5
are present in the Y, Z plane, and if an oblique reflecting surface
which appropriately reflects the reference axis ray is provided in
the first optical unit which is a fixed optical unit, the direction
of the reference axis which enters the variable magnification
optical system can be set to an arbitrary direction other than the
Y, Z plane, so that the degree of freedom of design of the
construction of an image pickup apparatus can be increased.
[0503] FIG. 65 is an explanatory view of a method of changing the
direction of the reference axis by forming the second optical
element B2 in Numerical Example 5 as a prism. As shown in FIG. 65,
a reflecting surface R4,1 which reflects an entering reference axis
ray parallel to the X axis in a direction parallel to the Z axis is
provided immediately after the fourth surface of the second optical
element B2 of Numerical Example 5. By forming the second optical
element B2 as the prism, the first optical unit which is a fixed
optical unit can be constructed as an optical unit whose entering
and exiting reference axes differ from each other 90.degree. in
direction. This construction makes it possible to reduce the
thickness of the second optical element B2 in the direction in
which a ray enters the second optical element B2, so that it is
possible to realize an image pickup apparatus which is extremely
thin in the direction in which a light beam from a subject enters
the variable magnification optical system.
[0504] [Numerical Example 6]
[0505] FIGS. 66, 67 and 68 are optical cross-sectional views taken
in the Y, Z plane, showing Numerical Example 6 relative to the
wide-angle end (W), the middle position (M) and the telephoto end
(T). Numerical Example 6 is a variable magnification optical system
having a magnification variation ratio of approximately 3.times..
Constituent data for Numerical Example 6 are shown below.
11 WIDE-ANGLE MIDDLE TELEPHOTO END POSITION END HORIZONTAL
HALF-ANGLE 26.0 18.0 9.2 OF VIEW VERTICAL HALF-ANGLE 20.0 13.6 6.9
OF VIEW APERTURE DIAMETER 1.40 2.00 2.80 IMAGE SIZE 4.8 .times. 3.6
mm i Yi Zi(W) .theta.i Di Ndi .nu.di 1 0.00 0.00 0.00 1.00 1 STOP
FIRST OPTICAL ELEMENT B1 (FIRST POSITIVE LENS) 2 0.00 1.00 0.00
8.00 1.58312 59.37 REFRACTING SURFACE 3 0.00 9.00 0.00 6.00 1
REFRACTING SURFACE SECOND OPTICAL ELEMENT B2 4 0.00 15.00 30.00
9.00 1 REFLECTING SURFACE 5 -7.79 10.50 15.00 9.00 1 REFLECTING
SURFACE 6 -12.29 18.29 -2.00 9.00 1 REFLECTING SURFACE 7 -16.24
10.21 -17.00 9.00 1 REFLECTING SURFACE 8 -24.03 14.71 -30.00 12.00
1 REFLECTING SURFACE 6/33 THIRD OPTICAL ELEMENT B3 (SECOND POSITIVE
LENS) 9 -24.03 2.71 0.00 1.00 1.76181 26.51 REFRACTING SURFACE 10
-24.03 1.71 0.00 VARIABLE 1 REFRACTING SURFACE FOURTH OPTICAL
ELEMENT B4 11 -24.03 -17.72 -30.00 VARIABLE 1 REFLECTING SURFACE 12
-33.56 -12.22 -15.00 11.00 1 REFLECTING SURFACE 13 -39.06 -21.75
0.00 11.00 1 REFLECTING SURFACE 14 -44.56 -12.22 15.00 11.00 1
REFLECTING SURFACE 15 -54.09 -17.72 30.00 VARIABLE 1 REFLECTING
SURFACE FIFTH OPTICAL ELEMENT B5 (NEGATIVE LENS) 16 -54.09 -3.29
0.00 0.70 1.51633 64.15 REFRACTING SURFACE 17 -54.09 -2.59 0.00
VARIABLE 1 REFRACTING SURFACE SIXTH OPTICAL ELEMENT B6 18 -54.09
6.30 30.00 11.00 1 REFLECTING SURFACE 19 -63.61 0.80 15.00 11.00 1
REFLECTING SURFACE 20 -69.11 10.32 0.00 11.00 1 REFLECTING SURFACE
21 -74.61 0.80 -15.00 11.00 1 REFLECTING SURFACE 22 -84.14 6.30
-30.00 VARIABLE 1 REFLECTING SURFACE 23 -84.14 -5.70 0.00 4.00
1.51633 64.15 FILTER 24 -84.14 -9.70 0.00 2.00 1 25 -84.14 -11.70
0.00 0.80 1.51633 64.15 COVER GLASS 26 -84.14 -12.50 0.00 1.00 1 27
-84.14 -13.50 IMAGE PLANE WIDE-ANGLE MIDDLE TELEPHOTO END POSITION
END D10 19.43 15.69 11.61 D15 12.50 9.26 5.72 D17 8.89 12.30 20.89
D17 10.39 13.34 20.78 R1-R10 Zi(M) = Zi(W) Zi(T) = Zi(W) R11-R15
Zi(M) = Zi(W) + 3.74 Zi(T) = Zi(W) + 7.82 R16-R17 Zi(M) = Zi(W)
Zi(T) = Zi(W) R18-R22 Zi(M) = Zi(W) + 3.41 Zi(T) = Zi(W) + 12.00
R23-R27 Zi(M) = ZI(W) Zi(T) = Zi(W) SPHERICAL SHAPE R2 R.sub.2 =
.infin. R3 R.sub.3 = -10.000 R9 R.sub.9 = -50.000 R10 R.sub.10 =
36.000 R16 R.sub.16 = -70.000 R17 R.sub.17 = 70.000 R23 R.sub.23 =
.infin. R24 R.sub.24 = .infin. R25 R.sub.25 = .infin. R26 R.sub.26
= .infin. ASPHERICAL SHAPE R4 C.sub.2 = -2.57907e-02 C.sub.20 =
-3.33716e-02 C.sub.03 = -4.87309e-05 C.sub.21 = -6.43446e-O5
C.sub.04 = -5.55902e-06 C.sub.22 = -6.87550e-05 C.sub.40 =
-3.54539e-05 R5 C.sub.02 = -4.07727e-03 C.sub.20 = -4.83586e-02
C.sub.03 = -3.29050e-04 C.sub.21 = -1.08808e-03 C.sub.04 =
-7.42806e-05 C.sub.22 = -1.42016e-04 C.sub.40 = 3.96524e-04 R6
C.sub.02 = -2.32622e-02 C.sub.20 = -3.78820e-02 C.sub.03 =
-1.21446e-05 C.sub.21 = 2.06307e-04 C.sub.04 = -2.33997e-05
C.sub.22 = -7.12505e-05 C.sub.40 = -6.10911e-05 R7 C.sub.02 =
-4.49711e-03 C.sub.20 = -3.61203e-02 C.sub.03 = 1.30552e-04
C.sub.21 = 2.06233e-03 C.sub.04 = -7.29751e-05 C.sub.22 =
-4.25831e-04 C.sub.40 = -2.55054e-04 R8 C.sub.02 = -2.27068e-02
C.sub.20 = -3.80000e-02 C.sub.03 = 5.79085e-06 C.sub.21 =
-4.79760e-04 C.sub.04 = -2.60268e-05 C.sub.22 = -4.20210e-05
C.sub.40 = -1.22588e-05 R11 C.sub.02 = 2.23034e-02 C.sub.20 =
3.21256e-02 C.sub.03 = 2.42570e-05 C.sub.21 = 2.65078e-05 C.sub.04
= 1.57855e-05 C.sub.22 = 5.20198e-05 C.sub.40 = 4.21383e-05 R12
C.sub.02 = 4.47467e-03 C.sub.20 = 1.74256e-02 C.sub.03 =
-2.20245e-04 C.sub.21 = -2.73590e-03 C.sub.04 = 1.90374e-05
C.sub.22 = 1.63565e-04 C.sub.40 = 1.29696e-04 R13 C.sub.02 =
1.15968e-02 C.sub.20 = 3.81521e-02 C.sub.03 = 1.48813e-04 C.sub.21
= 3.36024e-04 C.sub.04 = 2.46826e-05 C.sub.22 = 6.99720e-05
C.sub.40 = 5.08874e-05 R14 C.sub.02 = 2.46824e-03 C.sub.20 =
-2.74990e-02 C.sub.03 = 4.17008e-05 C.sub.21 = -1.86558e-03
C.sub.04 = 6.61747e-06 C.sub.22 = -4.34716e-05 C.sub.40 =
1.17941e-04 R15 C.sub.02 = 1.61390e-02 C.sub.20 = 2.51656e-02
C.sub.03 = 9.88747e-05 C.sub.21 = 6.61330e-05 C.sub.04 =
1.20942e-05 C.sub.22 = 8.53843e-05 C.sub.40 = 4.30022e-06 R18
C.sub.02 = -1.64464e-02 C.sub.20 = -1.33934e-02 C.sub.03 =
1.55688e-04 C.sub.21 = -4.52421e-04 C.sub.04 = 1.63771e-05 C.sub.22
= -2.79819e-05 C.sub.40 = 1.18921e-05 R19 C.sub.02 = -8.21811e-03
C.sub.20 = -1.69071e-02 C.sub.03 = 4.30452e-05 C.sub.21 =
2.62997e-04 C.sub.04 = -4.90960e-05 C.sub.22 = 5.55031e-05 C.sub.40
= 4.52979e-05 R20 C.sub.02 = -1.86035e-02 C.sub.20 = -2.12277e-02
C.sub.03 = -1.09892e-04 C.sub.21 = 2.65234e-04 C.sub.04 =
-2.09254e-05 C.sub.22 = -3.05974e-05 C.sub.40 = -9.75780e-06 R21
C.sub.02 = -9.99210e-03 C.sub.20 = -2.80526e-02 C.sub.03 =
-1.56705e-04 C.sub.21 = 1.56578e-03 C.sub.04 = -4.35488e-05
C.sub.22 = -1.62275e-04 C.sub.40 = -1.34152e-04 R22 C.sub.02 =
-1.65231e-02 C.sub.20 = -1.81685e-02 C.sub.03 = -6.45758e-05
C.sub.21 = -1.95699e-04 C.sub.04 = -5.30753e-06 C.sub.22 =
-1.00370e-05 C.sub.40 = -3.67285e-05
[0506] The construction of Numerical Example 6 will be described
below in order from its object side. The first surface R1 is an
aperture plane, and the first optical element B1 is a positive lens
which has the second surface R2 and the third surface R3. The
second optical element B2 has the fourth surface R4, the fifth
surface R5, the sixth surface R6, the seventh surface R7 and the
eighth surface R8, each of which is a surface mirror. The third
optical element B3 is a positive lens which has the ninth surface
R9 and the tenth surface R10.
[0507] The fourth optical element B4 has the eleventh surface R11
to the fifteenth surface R15 each of which is a surface mirror. The
fifth optical element B5 is a negative lens which has the sixteenth
surface R16 and the seventeenth surface R17. The sixth optical
element B6 has the eighteenth surface R18 to the twenty-second
surface R22 each of which is a surface mirror.
[0508] The twenty-third surface R23 to the twenty-sixth surface R26
are those of glass members such as a filter and a cover glass. The
twenty-seventh surface R27 is a final image plane in which the
image pickup surface of an image pickup medium such as a CCD is
positioned.
[0509] In the above construction, since the reflecting surfaces R18
to R22 of the sixth optical element B6 need be arranged so that
they can integrally move, the reflecting surfaces R18 to R22 are
integrally formed as shown in FIG. 69 by way of example. The fourth
optical element B4 and the second optical element B2 are also
integrally formed products.
[0510] The optical elements of Numerical Example 6 are grouped into
four optical units which constitute a variable magnification
optical system. Specifically, the stop R1, the first optical
element B1, the second optical element B2 and the third optical
element B3 constitute the first optical unit, the fourth optical
element B4 constitutes the second optical unit, the fifth optical
element B5 constitutes the third optical unit, and the sixth
optical element B6 constitutes the fourth optical unit. The second
and fourth optical units are magnification varying optical units
which vary the relative position therebetween to vary the
magnification of the variable magnification optical system. The
three optical unit is a fixed lens having a negative refractive
power, which is disposed between the two magnification varying
optical units. The concave reflecting surfaces R11, R13, R15, R18,
R20 and R22 effectively act to relay the aforesaid intermediate
images and pupil images in each of the magnification varying
optical units.
[0511] An image forming operation for an object lying at infinity
will be described below. First, a light beam passes through the
first optical element B1 (a first positive lens) and enters second
optical element B2. In the second optical element B2, the light
beam is reflected from surface to surface by the fourth surface R4
to the eighth surface R8, and then exits from second optical
element B2. During this time, a primary image is formed between the
fourth surface R4 and the fifth surface R5, while a secondary image
is formed between the eighth surface R8 and the ninth surface R9. A
pupil is formed between the sixth surface R6 and the seventh
surface R7.
[0512] Then, the light beam enters passes through the third optical
element B3 (a second positive lens) and enters the fourth optical
element B4. In the fourth optical element B4, the light beam is
reflected from surface to surface by the eleventh surface R11 to
the fifteenth surface R15, and then exits from fourth optical
element B4. During this time, a tertiary image is formed between
the twelfth surface R12 and the thirteenth surface R13 when the
focal length is at the wide-angle end, or between the thirteenth
surface R13 and the fourteenth surface R14 when the focal length is
at the telephoto end.
[0513] Then, the light beam passes through the fifth optical
element B5 (a negative lens) and enters the sixth optical element
B6. In the sixth optical element B6, the light beam is reflected
from surface to surface by the eighteenth surface R18 to the
twenty-second surface R22, and then exits from the sixth optical
element B6. During this time, a quaternary image is formed between
the eighteenth surface R18 and the nineteenth surface R19 when the
focal length is at the wide-angle end, or in the vicinity of the
nineteenth surface R19 when the focal length is at the telephoto
end. A pupil is formed between the twenty-first surface R21 and the
twenty-second surface R22 when the focal length is at the
wide-angle end, or between the twenty-second surface R22 and the
twenty-third surface R23 when the focal length is at the telephoto
end.
[0514] The light beam which has exited from the sixth optical
element B6 passes through the twenty-third surface R23 to the
twenty-sixth surface R26, and forms an object image on the
twenty-seventh surface R27 which is a quinary image forming
plane.
[0515] In Numerical Example 6, each of the second optical element
B2, the fourth optical element B4 and the sixth optical element B6
has an entering reference axis and an exiting reference axis which
differ from each other by 180.degree. in direction.
[0516] A magnification varying operation effected by the movements
of the respective optical elements will be described below. During
the magnification varying operation, the stop R1, the first optical
element B1, the second optical element B2 and the third optical
element B3 which constitute the first optical unit are fixed. As
the focal length varies from the wide-angle end toward the
telephoto end, the fourth optical element B4 moves in the Z plus
direction in parallel with the entering reference axis of the
fourth optical element B4, whereas the fifth optical element B5
which is a negative lens does not move. As the focal length varies
from the wide-angle end toward the telephoto end, the sixth optical
element B6 moves in the Z plus direction in parallel with the
entering reference axis of the sixth optical element B6. During the
magnification varying operation, the filter, the cover glass and
the final image plane do not move.
[0517] Thus, as the focal length varies from the wide-angle end
toward the telephoto end, the distance between the third optical
element B3 and the fourth optical element B4 is decreased, the
distance between the fourth optical element B4 and the fifth
optical element B5 is decreased, the distance between the fifth
optical element B5 and the sixth optical element B6 is increased,
and the distance between the sixth optical element B6 and the
twenty-third surface R23 is increased.
[0518] In addition, as the focal length varies from the wide-angle
end toward the telephoto end, the entire optical path length which
extends from the first surface R1 to the twenty-seventh surface R27
becomes temporarily shorter and then longer.
[0519] Each of FIGS. 70, 71 and 72 shows lateral aberration charts
of Numerical Example 6 relative to the wide-angle end (W), the
middle position (M) and the telephoto end (T). The respective
lateral aberration charts show lateral aberrations in the Y and X
directions, relative to six light beams which enter Numerical
Example 6 at different angles of incidence of (u.sub.Y, u.sub.X),
(0, u.sub.X), (-u.sub.Y, u.sub.X), (u.sub.Y, 0), (0, 0) and
(-u.sub.Y, 0), respectively. The horizontal axis of each of the
lateral aberration charts represents the height of incidence in the
Y or X direction of a light beam which is incident on each of the
entrance pupils.
[0520] As can be seen from these figures, Numerical Example 6 is
capable of achieving well-balanced correction of aberration at each
zoom position.
[0521] In addition, since Numerical Example 6 mainly uses surface
mirrors, no chromatic aberration occurs at any of the surface
mirrors, and an axial chromatic aberration and a lateral chromatic
aberration, both of which are chromatic aberrations occurring at
the first optical element B1 (the first positive lens), are
corrected by the fifth optical element B5 (negative lens) and the
third optical element B3 (the second positive lens), respectively,
so that the chromatic aberrations are corrected over the entire
magnification variation range. The third optical element B3 (second
positive lens) also serves as a field lens for forming a pupil at
an appropriate position in the fourth optical element B4.
[0522] In addition, the optical system of Numerical Example 6 is
approximately 12.8 mm thick for an image size of 4.8 mm.times.3.6
mm. In Numerical Example 6, particularly because each of the
optical elements and the entire optical system has a small
thickness and the reflecting surfaces of each of the optical
elements are formed on one plate, it is possible to readily
construct a variable magnification optical system which is thin as
a whole, by adopting a mechanism which causes two optical elements,
which are magnification varying optical units, to move along a
surface of one base plate.
[0523] Numerical Example 6 is the variable magnification optical
system in which, in the fifth embodiment shown in FIG. 49, the
first optical unit is formed as an optical unit having an entering
reference axis and an exiting reference axis which differ from each
other by 180.degree. in direction, and one fixed concave lens is
provided between the second optical unit 14 and the third optical
unit 15.
[0524] Incidentally, all the reference axes of Numerical Example 6
are present in the Y, Z plane, and if an oblique reflecting surface
which appropriately reflects the reference axis ray is provided in
the first optical unit which is a fixed optical unit, the direction
of the reference axis which enters the variable magnification
optical system can be set to an arbitrary direction other than the
Y, Z plane, so that the degree of freedom of design of the
construction of an image pickup apparatus can be increased.
[0525] FIG. 73 is an explanatory view of a method of changing the
direction of the reference axis by forming the first optical
element B1 in Numerical Example 6 as a prism. As shown in FIG. 73,
a reflecting surface R2,1 which reflects an entering reference axis
ray parallel to the X axis in a direction parallel to the Z axis is
provided immediately after the second surface R2 of the first
optical element B1 of Numerical Example 6. By forming the first
optical element B1 as the prism, the first optical unit which is a
fixed optical unit can be constructed as an optical unit whose
entering and exiting reference axes differ from each other
90.degree. in direction. This construction makes it possible to
reduce the thickness of the first optical element B1 in the
direction in which a ray enters the first optical element B1, so
that it is possible to realize an image pickup apparatus which is
extremely thin in the direction in which a light beam from a
subject enters the variable magnification optical system.
[0526] Values relative to each of the conditions for each of
Numerical Examples 4 to 6 are shown below. Incidentally, Conditions
1 and 2 are completely valid in all Numerical Examples 4 to 6.
However, the values of Condition 4 are 1.0 for all the suitable
reflecting surfaces of Numerical Examples 4 to 6, and 1.0 is within
the limits of Condition 4. Values relative to each of Conditions 3,
5 and 6 are shown below.
12 NUMERICAL NUMERAL NUMERICAL EXAMPLE 4 EXAMPLE 5 EXAMPLE 6
Condition 3 R11 1.06 R13 0.89 R11 0.93 R13 0.70 R15 0.59 R13 0.41
R15 0.73 R17 0.81 R15 0.86 R18 2.21 R20 0.98 R18 1.64 R20 1.00 R22
0.78 R20 1.17 R22 0.75 R24 0.91 R22 1.21 Condition 5 R11/R13 0.64
R13/R15 0.69 R11/R13 0.52 R13/R15 1.13 R15/R17 1.24 R13/R15 1.39
R18/R20 1.23 R20/R22 1.14 R18/R20 1.13 R20/R22 0.63 R22/R24 0.89
R20/R22 0.89 Condition 6 R10-R23 1.04 R12-R25 0.81 R11-R22 0.68
[0527] Each of Numerical Examples 4 to 6 is arranged to form an
object image at least once in each of the magnification varying
optical units, and can be realized as a variable magnification
optical system whose thickness is small in spite of its wide angle
of view. In addition, since decentered convex reflecting surfaces
each having a cross-sectional shape which is asymmetrical in a
plane containing entering and exiting reference axes are provided
in each of the magnification varying optical units, the optical
path in the variable magnification optical system is bent into a
desired shape so that the entire length of the variable
magnification optical system is reduced in a predetermined
direction. Accordingly, the variable magnification optical system
can be realized as a small-sized high-performance variable
magnification optical system which is fully corrected for
decentering aberration over the entire magnification variation
range.
[0528] In accordance with the present invention having the
aforesaid arrangement and construction, a variable magnification
optical system, in which a fixed optical unit and a plurality of
magnification varying optical units are arranged in that order from
an object side and the magnification of the variable magnification
optical system is varied by the relative movement between the
plurality of magnification varying optical units, can be realized
as a high-performance variable magnification optical system which
has a small thickness in spite of its wide angle of view, an entire
length which is short in a predetermined direction, and decentering
aberration which is fully corrected over the entire magnification
variation range. In addition, an image pickup apparatus using such
high-performance variable magnification optical system is
achieved.
[0529] In addition, it is possible to achieve a variable
magnification optical system having at least one of the following
effects and advantages, and an image pickup apparatus employing
such a variable magnification optical system.
[0530] Since a stop is arranged on the object side of the variable
magnification optical system or in the vicinity of the first
surface and an object image is formed at least once in the variable
magnification optical system, the thickness of the variable
magnification optical system can be made small in spite of its wide
angle of view.
[0531] Since each optical unit employs an optical element having a
plurality of reflecting surfaces having appropriate refractive
powers and the reflecting surfaces are arranged in a decentered
manner, the optical path in the variable magnification optical
system can be bent into a desired shape to reduce the entire length
of the variable magnification optical system in a predetermined
direction.
[0532] Each optical element which constitutes part of the variable
magnification optical system includes a plurality of reflecting
surfaces which are integrally formed in such a manner that each of
the reflecting surfaces is arranged in a decentered manner and is
given an appropriate refractive power. Accordingly, the decentering
aberration of the variable magnification optical system can be
fully corrected over the entire magnification variation range.
[0533] Since each magnification varying optical unit employs an
optical element in which a plurality of curved or plane reflecting
surfaces are integrally formed, not only is it possible to reduce
the entire size of the variable magnification optical system, but
it is also possible to solve the problem of excessively strict
arrangement accuracy (assembly accuracy) which would have often
been experienced with reflecting surfaces.
* * * * *