U.S. patent application number 09/255328 was filed with the patent office on 2002-01-03 for image pickup optical system.
Invention is credited to NANBA, NORIHIRO.
Application Number | 20020001146 09/255328 |
Document ID | / |
Family ID | 13197223 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001146 |
Kind Code |
A1 |
NANBA, NORIHIRO |
January 3, 2002 |
IMAGE PICKUP OPTICAL SYSTEM
Abstract
An image pickup optical system includes an optical unit having a
light incidence surface on which a light is incident, a light
reflecting surface reflecting the light incident from the light
incidence surface and having a curvature, and a light emergence
surface from which the light reflected by the light reflecting
surface emerges, and a transparent optical member disposed near the
surface position of at least one of the light incidence surface and
the light emergence surface. The optical member is adhesively fixed
to the optical unit to thereby make any special holding member for
the optical member relative to the optical unit unnecessary.
Inventors: |
NANBA, NORIHIRO;
(KANAGAWA-KEN, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
13197223 |
Appl. No.: |
09/255328 |
Filed: |
February 23, 1999 |
Current U.S.
Class: |
359/834 |
Current CPC
Class: |
G02B 27/09 20130101;
G02B 2027/0138 20130101; G02B 27/0101 20130101 |
Class at
Publication: |
359/834 |
International
Class: |
G02B 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 1998 |
JP |
10-062337 |
Claims
What is claimed is:
1. An image pickup optical system comprising: an optical unit
having a light incidence surface on which a light is incident, a
light reflecting surface reflecting the light incident from said
light incidence surface and having a curvature, and a light
emergence surface from which the light reflected by said light
reflecting surface emerges; and a transparent optical member
disposed near the surface position of at least one of said light
incidence surface and said light emergence surface; said optical
member being fixed to said optical unit.
2. An image pickup optical system according to claim 1, wherein
said light reflecting surface is provided in a plurality.
3. An image pickup optical system according to claim 1, wherein
said optical member is an optical low-pass filter.
4. An image pickup optical system according to claim 1, wherein
said optical member is an infrared cut filter.
5. An image pickup optical system according to claim 1, wherein
said light incidence surface has its concave surface facing in the
direction of travel of the light, and said optical member is
disposed forwardly of said light incidence surface.
6. An image pickup optical system according to claim 1, wherein
said light emergence surface has negative refractive power, and
said optical member is disposed rearwardly of said light emergence
surface.
7. An image pickup optical system according to claim 1, wherein
said optical member is a prism having a reflecting surface
reflecting the light.
8. An image pickup optical system according to claim 7, wherein the
reflecting surface of said prism is a half mirror.
9. An image pickup optical system according to claim 1, wherein the
light beam having emerged from said optical unit is converged and
imaged, and an image pickup unit is disposed on the imaging
plane.
10. An image pickup optical system according to claim 9, wherein
cover glass is fixed forwardly of said image pickup unit, and said
optical member corresponds to said cover glass.
11. An image pickup optical system according to claim 1, wherein
said optical member is adhesively fixed to said optical unit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an optical unit and an optical
system using the same, and particularly is suitable for a video
camera or a still video camera and a copying apparatus or the like
utilizing an optical unit comprising a plurality of reflecting
surfaces each having a curvature constructed integrally with one
another.
[0003] 2. Related Background Art
[0004] There have heretofore been proposed various photographing
optical systems utilizing the reflecting surface of a concave
mirror, a convex mirror or the like. FIG. 6 of the accompanying
drawings is a schematic view of the essential portions of a
so-called mirror optical system (reflecting optical system)
comprising a concave mirror and a convex mirror.
[0005] In the mirror optical system of FIG. 6, an object light beam
124 from an object is reflected by a concave mirror 121 and travels
toward the object side while being converged, and is reflected by a
convex mirror 122, whereafter it is imaged on an image plane
123.
[0006] This mirror optical system is based on the construction of a
so-called Cassegrainian reflector, and is directed to shorten the
full length of the optical system by bending the optical path of a
telephoto lens system of a great full lens length comprised of a
refracting lens by the use of two reflecting mirrors opposed to
each other.
[0007] Also in an objective lens system constituting a telescope,
for a similar reason, there are known a number of types for
shortening the full length of the optical system by the use of a
plurality of reflecting mirrors, besides the Cassegrainian
type.
[0008] As described above, heretofore, by using a reflecting mirror
instead of the lens of a photo-taking lens of a great full lens
length, the optical path is efficiently bent to thereby provide a
compact mirror optical system.
[0009] Generally, however, in a mirror optical system such as a
Cassegrainian reflector, there is the problem that a part of the
object ray of light is eclipsed by the convex mirror 122. This
problem is attributable to the fact that the convex mirror 122 is
present in the passage area of the object light beam 124.
[0010] In order to solve this problem, there has also been proposed
a mirror optical system in which a reflecting mirror is made
eccentric and used to avoid the other portion of the optical system
shielding the passage area of the object light beam 124, i.e.,
separate the principal ray 126 of the light beam from an optical
axis 125.
[0011] FIG. 7 of the accompanying drawings is a schematic view of
the essential portions of a mirror optical system disclosed in U.S.
Pat. No. 3,674,334, and this mirror optical system separates the
principal ray of an object light beam from an optical axis to
thereby solve the above-noted problem of eclipse. The mirror
optical system of FIG. 7 has, in the order of passage of the light
beam, a concave mirror 131, a convex mirror 133, and they are
originally reflecting mirrors rotation-symmetrical with respect to
an optical axis 134, as indicated by dots-and-dash lines in FIG. 7.
Of these mirrors, use is made of only the upper side of the concave
mirror 131 relative to the optical axis 134 as viewed in the plane
of the drawing sheet, only the lower side of the convex mirror 132
relative to the optical axis 134 as viewed in the plane of the
drawing sheet, and only the lower side of the convex mirror 133
relative to the optical axis 134 as viewed in the plane of the
drawing sheet to thereby construct an optical system in which the
principal ray 136 of the object light beam 135 is separated from
the optical axis 134 to thereby eliminate the eclipse of the object
light beam 135.
[0012] FIG. 8 of the accompanying drawings is a schematic view of
the essential portions of a mirror optical system disclosed in U.S.
Pat. No. 5,063,586. The mirror optical system of FIG. 8 solves the
above-noted problem by making the central axis itself of a
reflecting mirror eccentric relative to an optical axis and
separating the principal ray of an object light beam from the
optical axis.
[0013] When in FIG. 8, the vertical axis of an object surface 141
is defined as an optical axis 147, the central coordinates of the
respective reflecting surfaces of a convex mirror 142, a concave
mirror 143, a convex mirror 144 and a concave mirror 145 in the
order of passage of the light beam and the central axes (axes
passing through the centers of the reflecting surfaces and the
centers of curvature of those surfaces) 142A, 143A, 144A and 145A
are decentering or eccentric relative to the optical axis 147. In
FIG. 8, the amount of eccentricity at this time and the radius of
curvature of each surface are appropriately set to thereby prevent
the eclipse of the object light beam 148 by each reflecting mirror,
and efficiently form an object image on an imaging plane 146.
[0014] Besides the aforementioned patents, U.S. Pat. Nos. 4,737,021
and 4,265,510 disclose a construction in which use is made of a
part of a reflecting mirror rotation-symmetrical with respect to an
optical axis to avoid eclipse, or a construction in which the
central axis itself of a reflecting mirror is made eccentric
relative to an optical axis to thereby avoid eclipse.
[0015] Now, as a catadioptric optical system using both of a
reflecting mirror and a refracting lens and having a focal length
changing function, there are, for example, the deep sky telescopes
of U.S. Pat. Nos. 4,477,456 and 4,571,036. These use a parabolic
reflecting mirror as a main mirror and use an Elfre eyepiece mirror
to make the magnification variable.
[0016] Also, there is known the zooming technique of moving the
plurality of reflecting surfaces constituting the above-described
mirror optical system relative to one another to thereby vary the
imaging magnification (focal length) of the photo-taking optical
system. For example, in U.S. Pat. No. 4,812,030, in the
construction of the Cassegrainian reflector shown in FIG. 6, there
is disclosed the technique of varying the spacing from the concave
mirror 121 to the convex mirror 122 and the spacing from the convex
mirror 122 to the image plane 123 relative to each other to thereby
effect the focal length change of the photo-taking optical
system.
[0017] FIG. 9 of the accompanying drawings shows another embodiment
disclosed in the same publication. In FIG. 9, an object light beam
158 from an object impinges on a first concave mirror 151 and is
reflected by the surface thereof and becomes a convergent light
beam and travels toward the object side, and impinges on a first
convex mirror 152, by which it is reflected toward the imaging
plane side and becomes a substantially parallel light beam and
impinges on a second convex mirror 154, and is reflected by the
surface thereof and becomes a divergent light beam and impinges on
a second concave mirror 155, by which it is reflected and becomes a
convergent light beam and is imaged on an image plane 157. In this
construction, the spacing between the first concave mirror 151 and
the first convex mirror 152 is varied and also the spacing between
the second convex mirror 154 and the second concave mirror 155 is
varied to thereby effect zooming and vary the focal length of the
entire mirror optical system.
[0018] Also, in U.S. Pat. No. 4,993,818, the image formed by the
Cassegrainian reflector shown in FIG. 6 is secondarily formed by
another mirror optical system provided at the subsequent stage, and
the imaging magnification of this mirror optical system for
secondary imaging is varied to thereby effect the focal length
change of the entire photo-taking system.
[0019] These photo-taking optical systems of the reflection type
have required many constituents, and to obtain the necessary
optical performance, it has been necessary to assemble respective
optical parts with good accuracy. Particularly, the accuracy of the
quickly retracted positions of the reflecting mirrors is severe and
therefore, the adjustment of the position and angle of each
reflecting mirror has been requisite.
[0020] As a method of solving this problem, there has been proposed
a method of making, for example, the mirror system into a block to
thereby avoid the incorporation errors of the optical parts caused
during the assembly thereof.
[0021] As prisms in which a number of reflecting surfaces are made
into a block, there have heretofore been optical prisms such as a
pentagonal roof prism, an optical prism such as a porro prism used
in the finder system of a camera, and a color resolving prism for
resolving a light beam from a photo-taking lens into three color
lights, e.g., red, green and blue lights, and imaging object images
based on the respective color lights on the surfaces of
corresponding image pickup elements.
[0022] These prisms have a plurality of reflecting surfaces molded
integrally with one another and therefore, the relative positional
relation among the reflecting surfaces is made accurately and the
positional adjustment among the reflecting surfaces becomes
unnecessary. However, the main function of these prisms is to
change the direction of travel of rays of light to thereby effect
the reversal of an image, and each reflecting surface is formed by
a flat surface.
[0023] In contrast, there is also known an optical system in which
the reflecting surface of a prism is given a curvature.
[0024] FIG. 10 of the accompanying drawings is a schematic view of
the essential portions of an observation optical system disclosed
in U.S. Pat. No. 4,775,217. This observation optical system is an
optical system through which as outside scene is observed and also
a display image displayed on an information displaying member is
observed in overlapping relationship with the scene.
[0025] In this observation optical system, a display light beam 165
emitted from a display image on the information displaying member
161 is reflected by a surface 162 and travels toward the object
side, and impinges on a half mirror surface 163 comprising a
concave surface. The light beam is reflected by this half mirror
surface 163, whereafter the display light beam 165 is made into a
substantially parallel light beam by the refractive power of the
concave surface 163, and is refracted by and transmitted through
the surface 162, whereafter it forms the enlarged virtual image of
the display image and also enters an observer's pupil 164 to
thereby make the observer recognize the display image.
[0026] On the other hand, an object light beam 166 from an object
enters a surface 167 substantially parallel to the reflecting
surface 162, and is refracted thereby and passes to the concave
half mirror surface 163. Semi-transmitting film is deposited by
evaporation on the concave surface 163, and a part of the object
light beam 166 is transmitted through the concave surface 163, and
is refracted by and transmitted through the surface 162, whereafter
it enters the observer's pupil 164. Thereby the observer visually
confirms the display image in overlapping relationship with the
outside scene.
[0027] FIG. 11 of the accompanying drawings is a schematic view of
the essential portions of an observation optical system disclosed
in Japanese Patent Application Laid-Open No. 2-297516. This
observation optical system also is an optical system through which
an outside scene is observed and a display image displayed on an
information displaying member is observed in overlapping
relationship with the scene.
[0028] In this observation optical system, a display light beam 174
emitted from the information displaying member 170 is transmitted
through a flat surface 177 constituting a prism Pa and enters the
prism Pa and impinges on a parabolic reflecting surface 171. The
display light beam 174 is reflected by this reflecting surface 171
and becomes a convergent light beam and is imaged on a focal plane
176. At this time, the display light beam 174 reflected by the
reflecting surface 171 has arrived at the focal plane 176 while
being totally reflected between two parallel flat surfaces 177 and
178 constituting the prism Pa, whereby the thinning of the entire
optical system is achieved.
[0029] The display light beam 174 emerging as a divergent light
from the focal plane 176 then enters a half mirror 172 comprising a
parabolic surface while being totally reflected between the flat
surface 177 and the flat surface 178, and is reflected by this half
mirror surface 172 and at the same time, forms the enlarged virtual
image of the display image by the refractive power thereof and
becomes a substantially parallel light beam, and is transmitted
through the surface 177 and enters an observer's pupil 173 to
thereby make the observer recognize the display image.
[0030] On the other hand, an object light beam 175 from the outside
is transmitted through a surface 178b constituting a prism Pb, and
is transmitted through the half mirror 172 comprising a parabolic
surface, and is transmitted through the surface 177 and enters the
observer's pupil 173. The observer visually confirms the display
image in overlapping relationship with the outside scene.
[0031] Further, optical heads for light pickup using an optical
element having a surface of a prism made into a reflecting surface
are disclosed, for example, in Japanese Patent Application
Laid-Open No. 5-12704 and Japanese Patent Application Laid-Open No.
6-139612. These reflect a light from a semiconductor laser by a
Fresnel surface or a hologram surface, and thereafter images it on
a disc surface, and directs the reflected light from the disc to a
detector.
[0032] Here, in any of the mirror optical systems having an
eccentric mirror which are disclosed in the aforementioned U.S.
Pat. Nos. 3,674,334, 5,063,586 and 4,265,510, each reflecting
mirror is disposed with a different amount of eccentricity and the
mounting structure for each reflecting mirror is very cumbersome
and it is very difficult to secure mounting accuracy.
[0033] Also, in any of the photographing optical systems having the
focal length changing function which are disclosed in U.S. Pat.
Nos. 4,812,030 and 4,993,818, the number of constituent parts such
as reflecting mirrors and an imaging lens is great, and to obtain
necessary optical performance, it has been necessary to assemble
the respective optical parts with good accuracy.
[0034] Also, particularly the accuracy of the relative position of
the reflecting mirrors becomes severe and therefore, it has been
necessary to effect the adjustment of the position and angle of
each reflecting mirror.
[0035] Also, the photographing optical system of the reflection
type according to the prior art is of a construction suitable for a
lens system of the so-called telephoto type in which the full
length of the optical system is great and the angle of view is
small. To provide a photographing optical system which requires the
angle of view of a standard lens to the angle of view of a wide
angle lens, the number of reflecting surfaces required in
aberration correction becomes great and therefore, higher accuracy
of parts and higher accuracy of assembly become necessary, and this
has led to a tendency toward a higher cost or the bulkiness of the
whole.
[0036] Also, the observation optical systems disclosed in the
aforementioned U.S. Pat. No. 4,775,217 and Japanese Patent
Application Laid-Open No. 2-297516 aim principally at the pupil
imaging action for efficiently transmitting to the observer's pupil
the display image displayed on the information displaying member
disposed separately from the observer's pupil, and changing the
direction of travel of rays of light, and these publications do not
directly disclose the technique of effecting positive aberration
correction by a reflecting surface having a curvature. Also, the
optical systems for light pickup disclosed in Japanese Patent
Application Laid-Open No. 5-12704 and Japanese Patent Application
Laid-Open No. 6-139612 are both restricted to the use of a
detecting optical system, and have not satisfied the imaging
performance for a photographing optical system, particularly an
image pickup device using an image pickup element of the area type
such as a CCD.
[0037] In contrast, the applicant of the basic application filed in
Japan discloses in Japanese Patent Application Laid-Open No.
8-292371 an optical element in which a refracting surface on which
a light beam is incident, a plurality of reflecting surfaces each
having a curvature, and refracting surface from which light beams
reflected by these reflecting surfaces emerge are integrally molded
on the surface of a transparent member, and an optical system using
the same.
[0038] By using such an optical element, there is provided an
optical system in which the compactness of an entire mirror optical
system is achieved and yet the disposition accuracy (assembly
accuracy) of a reflecting mirror liable to be in the mirror optical
system is relaxed. Also, by adopting a construction in which a stop
is disposed most adjacent to the object side of an optical system
and an object image is formed at least once in the optical system,
the shortening of the effective diameter of the optical system is
achieved inspite of being an optical system having a wide angle of
view. Appropriate refractive power is given to a plurality of
reflecting surfaces constituting optical elements, and a reflecting
surface constituting each optical element is eccentrically disposed
to thereby provide an optical system in which the optical path is
bent into a desired shape and of which the full length in a
predetermined direction is shortened.
[0039] In the optical element proposed in the aforementioned
Japanese Patent Application Laid-Open No. 8-292371, a method of
holding other optical part such as an optical filter than an
imaging optical system has not been particularly referred to.
SUMMARY OF THE INVENTION
[0040] It is an object of the present invention to provide an
optical unit in which an incidence surface on which a light beam is
refracted and incident, a plurality of reflecting surfaces each
having a curvature for successively reflecting the incident light
beam, and an emergence surface from which the light beam reflected
by the plurality of reflecting surfaces is refracted and emerges
are integrally formed on the surface of a transparent member,
wherein an optical member such as an optical filter is adhesively
secured to the incidence surface and/or the emergence surface,
whereby any special holding member for the optical member is made
unnecessary and the simplification of the entire device is
achieved, and an optical system using the same.
[0041] It is also an object of the present invention to provide an
optical system in which a solid state image pickup element is
adhesively secured to the optical unit to thereby effect the
positioning of the two, and any positional deviation after the
manufacture of the optical system is prevented.
[0042] It is also an object of the present invention to provide an
optical unit in which the area of contact of the optical effective
portion of the optical member or the solid state image pickup
element with the atmosphere is decreased to thereby reduce the
influence of dust, and an optical system using the same.
[0043] The optical unit of the present invention is characterized
in that an incidence surface on which a light beam is incident, a
plurality of reflecting surfaces each having a curvature for
successively reflecting the light beam from the incidence surface,
and an emergence surface from which the light beam reflected by the
plurality of reflecting surfaces emerges are integrally formed on
the surface of a transparent member, and a light transmitting
member is fixed near said incidence surface and/or the emergence
surface.
[0044] The optical unit of the present invention is particularly
characterized in that
[0045] the light transmitting member is adhesively fixed,
[0046] another light transmitting member is adhesively fixed to the
light transmitting member,
[0047] the light transmitting member is adhesively fixed to the
flat portion of the incidence surface and/or the emergence
surface,
[0048] the light transmitting member is an optical low-pass filter
or an infrared cut filter,
[0049] the another light transmitting member is cover glass
covering the image pickup surface of the solid state image pickup
element, and
[0050] the light transmitting member is a prism having a reflecting
surface.
[0051] The optical system of the present invention is characterized
by at least one optical unit of the above-described
construction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 shows the construction of an optical system according
to Embodiment 1 of the present invention.
[0053] FIG. 2 is a perspective view showing the construction of the
optical system according to Embodiment 1 of the present
invention.
[0054] FIG. 3 shows the construction of an optical system according
to Embodiment 2 of the present invention.
[0055] FIG. 4 shows the construction of an optical system according
to Embodiment 3 of the present invention.
[0056] FIG. 5 shows the construction of an optical system according
to Embodiment 4 of the present invention.
[0057] FIG. 6 shows the basic construction of a Cassegrainian
reflector according to the prior art.
[0058] FIG. 7 is a schematic view of the essential portions of a
mirror optical system according to the prior art.
[0059] FIG. 8 is a schematic view of the essential portions of a
mirror optical system according to the prior art.
[0060] FIG. 9 is a schematic view of the essential portions of a
mirror optical system according to the prior art.
[0061] FIG. 10 is a schematic view of an observation optical system
according to the prior art.
[0062] FIG. 11 is a schematic view of an observation optical system
according to the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0063] In the optical system of the present embodiment, there is
not a symmetry axis like an optical axis in a conventional optical
system. So, a "reference axis" is set in the optical system and
with this reference axis as the base, the construction of elements
in the optical system will hereinafter be described.
[0064] The definition of the reference axis will first be
described. Generally, the optical path of a certain ray of light of
a reference wavelength which is the reference from the object plane
to the image plane is defined as the "reference axis" in the
optical system. By this alone, the ray of light which is the
reference is not defined and therefore, usually the reference axis
ray of light is set in conformity with the following two
principles.
[0065] (1) When an axis having symmetry even partially exists in an
optical system and the collection of aberrations can be effected
with good symmetry, a ray of light passing on an axis having the
symmetry is defined as a reference axis ray of light.
[0066] (2) When a symmetry axis generally does not exist in an
optical system or when the collection of aberrations cannot be
effected with good symmetry even if a symmetry axis exists
partially, a ray of light emerging from the center of an object
plane (the center of a range to be photographed and observed) and
passing through the optical system in the order of the designated
surfaces of the optical system and passing through the center of a
stop in the optical system, or passing through the center of the
stop in the optical system to the center of the last image plane is
set as a reference axis ray of light, and the optical path thereof
is defined as a reference axis.
[0067] Some embodiments of the optical system of the present
invention will now be described.
[0068] FIG. 1 is a schematic view of the essential portions of
Embodiment 1 of an optical system using the optical unit of the
present invention. An optical path is also shown in FIG. 1. In FIG.
1, reference numeral 1 designates an off-axial optical unit
provided with a plurality of curved reflecting surfaces and formed
of a transparent material such as glass. The optical unit 1
includes, in the order of passage of a ray of light from an object,
a reflecting surface (incidence surface) R1 having negative
refractive power and having its concave surface facing in the
direction of travel of the light, five reflecting surfaces, i.e., a
concave mirror R2, a convex mirror R3, a concave mirror R4, a
convex mirror R5 and a concave mirror R6, and a refracting surface
(emergence surface) R7 having negative refractive power and having
its convex surface facing in the direction of travel of the light.
Reference numeral 5 denotes a stop (entrance pupil) disposed on the
object side of the optical unit 1.
[0069] Reference numeral 2 designates an optical correcting plate
(light transmitting member) such as a low-pass filter (rock crystal
plate) or an infrared cut filter adhesively fixed to the emergence
surface R7 of the optical unit 1. Reference numeral 3 denotes cover
glass covering a solid state image pickup element 4.
[0070] Reference character 4a designates the last image plane on
which the image pickup surface of the image pickup element image
pickup medium) 4 such as a CCD is positioned. Reference numeral 6
denotes the reference axis of the present optical system which
passes through the center of the stop 5 to the center of the last
image plane 4a.
[0071] The reflecting surfaces R2 to R6 comprise off-axial
reflecting surfaces so disposed as to be filted with respect to the
reference axis 6.
[0072] The two refracting surfaces R1 and R7 both comprise
rotation-symmetrical spherical surfaces, aspherical surfaces or
flat surfaces. Thereby, the condition for the correction of
chromatic aberration is satisfied and the reference axis can be
accurately set when the optical system is manufactured and
evaluated. Also, the refracting surfaces are made
rotation-symmetrical to thereby reduce the creation of asymmetrical
chromatic aberration. Also, all the reflecting surfaces are
surfaces symmetrical with respect to YZ plane.
[0073] The two refracting surfaces R1 and R7 may be comprised of
rotation-symmetrical surfaces, for example, an anamorphic
aspherical surfaces.
[0074] The imaging action in the present embodiment will now be
described. A light beam 7 from an object has its quantity of
incident light regulated by the stop 5, whereafter it is refracted
by and enters the incidence surface R1 of the optical unit 1, and
is reflected by the surface R2, and thereafter is once imaged at
the position N1 between the surface R2 and the surface R3, and then
is reflected by the surfaces R3, R4, R5 and R6 in succession, and
is refracted by and emerges from the emergence surface R7, and
passes through the optical correcting plate 2 and the cover glass
3, and is re-imaged on the last image plane 4a of the image pickup
element 4.
[0075] The light beam which has entered from the surface R1 as
described above is intermediately imaged in the optical unit 1.
Thereby, the optical system is made thin in a direction
perpendicular to the plane of the drawing sheet of FIG. 1, and the
off-axial principal ray of light which has emerged from the stop 5
is converged before it is greatly widened, and an increase in the
effective diameter of each of the first reflecting surface R2 and
subsequent surfaces by the wider angle of the optical system is
suppressed.
[0076] The reference axis in the present embodiment is on the plane
of the drawing sheet (YZ plane).
[0077] Thus, the optical unit 1 achieves desired optical
performance by the incidence and emergence surfaces and the
plurality of curved reflecting mirrors therein, and functions as a
lens unit having the imaging action as a whole.
[0078] Each reflecting surface constituting the optical unit 1 is a
so-called eccentric reflecting surface in which the normal at the
point of intersection between the incident and emergent reference
axis and the reflecting surface does not coincide with the
reference axis. This prevents the eclipse occurring in the mirror
optical system according to the prior art and also thereby
constitutes a compact off-axial optical unit of a free shape which
adopts a freer arrangement and is good in space efficiency.
[0079] Further, each reflecting surface is of a shape in which
refractive power differs in two planes (yz plane and xz plane)
orthogonal to each other and which has only one symmetrical
surface. Thereby, the eccentric aberration caused by each
reflecting surface being eccentrically disposed is suppressed.
[0080] In the optical unit 1 constituting the optical system of the
present embodiment, the plurality of reflecting surfaces each
having a curvature are constructed integrally with one another and
therefore, a barrel for holding a plurality of lenses in an
ordinary refracting optical system is unnecessary. Also, the
construction shown in FIG. 1 is such that the entire optical system
can be held if there are a holding member for the solid state image
pickup element 4, a holding member for positioning the optical unit
1 relative to the image pickup surface of the solid state image
pickup element 4 and a holding member for the stop 5.
[0081] Also, design is made such that the light beam having emerged
from the optical unit 1 passes through the optical correcting plate
and the cover glass 3 and thereafter, again forms an image on the
image pickup surface of the solid state image pickup element 4, and
the optical unit 1 at this time functions as a lens unit having
desired optical performance and having the imaging action as a
whole while repeating the reflection by the plurality of reflecting
mirrors each having a curvature.
[0082] FIG. 2 is a perspective view of the optical unit shown in
FIG. 1. In FIG. 2, the same reference characters as those in FIG. 1
designate the same parts. Also, in FIG. 2, the letter A designates
a flat surface portion provided on the outer periphery of the
incidence refracting surface R1, i.e., a location through which the
effective light beam does not pass, and the letter B denotes a flat
surface portion provided on the outer periphery of the emergence
refracting surface R7. The flat surface portions A and B are
basically surfaces perpendicular to the reference axis 6, and are
formed on the surface of the optical unit 1 so that the flat
surface portion A may be located on the object side from the
refracting surface R1 and the flat surface portion B may be located
on the image plane side from the refracting surface R7.
[0083] In the present embodiment, the optical correcting plate 2 is
adhesively secured to the flat surface portion B located near the
emergence refracting surface R7 of the optical unit 1. By doing so,
a holding member for holding the optical correcting plate 2 is made
unnecessary. Also, the simplification by the curtailment of the
number of parts and the downsizing of the optical system by a
decrease in volume corresponding to the absence of the holding
member are made possible.
[0084] Also, the refracting surface R7 is hermetically sealed by
the optical correcting plate 2, whereby the refracting surface R7
and that surface of the optical correcting plate 2 which is
adjacent to the refracting surface R7 are shielded from the
atmosphere, and the area of contact with the atmosphere in the
optical unit 1 is decreased to thereby reduce the influence of dust
on the optical system.
[0085] FIG. 3 is a cross-sectional view of the essential portions
of Embodiment 2 of the present invention. This embodiment differs
from the Embodiment 1 of FIG. 1 only in that an optical correcting
plate 31 such as an infrared cut filter is adhesively fixed to the
incidence surface R1, and in the other points, the construction of
this embodiment is the same as that of Embodiment 1.
[0086] Reference numeral 32 designates an optical low-pass filter.
In the present embodiment, the optical correcting plate is
adhesively secured divisionally to the incidence side and emergence
side of the optical unit 1 to thereby make the thickness of the
correcting plate on the emergence side small. Thereby, the optical
design of the optical unit 1 more shortened in its back focal
length is made possible. Generally, in a CCD, when light is
incident on the image pickup surface thereof at a great angle of
incidence, a problem such as color irregularity arises and
therefore, it is required in an image pickup optical system for the
exit pupil thereof to be made as far as possible from the image
plane and telecentric. In the optical unit 1 shown in FIG. 3, when
the exit pupil is equidistant from the image plane, it leads to the
possibility of making the optically effective area of the concave
mirror R6 which is the last reflecting surface smaller to shorten
the back focal length. In the present embodiment, by so
constructing, the thickness of the emergence side of the optical
unit 1 in x direction is made small.
[0087] FIG. 4 is a cross-sectional view of the essential portions
of Embodiment 3 of the present invention. This embodiment differs
from the Embodiment 1 of FIG. 1 only in that the optical correcting
plate 2 and the cover glass 3 protecting the image pickup element
are adhesively fixed, and in the other points, the construction of
this embodiment is the same as that of Embodiment 1.
[0088] In the present embodiment, the adherence of dust is
completely prevented in such a manner that the optically effective
portion near the imaging plane does not at all contact with air,
thereby obtaining good images.
[0089] Also, in order to prevent the irregularity of the position
of the image pickup surface relative to the mounted position of the
solid state image pickup element in the direction of the reference
axis, the focus adjustment of the optical system to be effected
after the mounting of the solid state image pickup element is made
unnecessary by using the surface of the cover glass as a mounting
surface in the present embodiment, and also sufficiently
controlling the accuracy of molding of the optical unit 1, the
accuracy of the thickness and optical path length of the optical
correcting plate 2, and the positional accuracy of the surface of
the cover glass and the image pickup surface.
[0090] FIG. 5 is a cross-sectional view of the essential portions
of Embodiment 4 of the present invention. This embodiment differs
from the Embodiment 1 of FIG. 1 only in that two solid state image
pickup elements 4a and 4b are provided for an optical unit 1
through a half mirror surface 52 and cover glasses 3a and 3b are
provided for the optical correcting plate 2 and respective solid
state image pickup elements 41 and 42, and in the other points, the
construction of this embodiment is the same as that of Embodiment
1.
[0091] The cover glasses 3a and 3b are disposed while being
adhesively secured to a beam splitter 51. The beam splitter 51 is
of a construction in which two triangular prisms are joined
together, and reference numeral 52 designates the joined surface. A
half mirror coat is provided on the joined surface 52, and a light
beam incident on the beam splitter 51 is separated into a
transmitted light and a reflected light by the joined surface 52,
and the transmitted light passes through the cover glass 3a and
forms an image on the image pickup surface 4a of the solid state
image pickup element 41, and the reflected light passes through the
cover glass 3b and forms an image on the image pickup surface 4b of
the solid state image pickup element 41. Here, for example, the
solid state image pickup elements 41 and 42 are in a positional
relation wherein they deviate from each other by a half pixel pitch
relative to the reference axis indicated by dot-and-dash line, and
the two images are combined together to thereby obtain an image of
higher resolution than that by a single solid state image pickup
element, by the so-called pixel deviating effect.
[0092] In the present embodiment, two solid state image pickup
elements are adhesively secured to the beam splitter. Here,
adjustment is done so as to provide the above-described positional
relation during adhesive securing, whereafter the adhesive securing
is effected to thereby ensure the accuracy of the amount of pixel
deviation. Also, in the present embodiment, the optical members
from the optical unit 1 to the solid state image pickup elements
41, 42 are all adhesively fixed to thereby prevent any positional
deviation, any change in posture, etc. after the manufacture.
[0093] When the optical correcting plate 2 is unnecessary, the beam
splitter 51 is adhesively secured to the optical unit 1. Also, the
beam splitter may be a color resolving prism system using not only
a half coat, but also a total reflection surface to obtain a
similar effect.
[0094] According to the present invention, as described above,
there can be achieved an optical unit in which an incidence surface
on which a light beam is refracted and incident, a plurality of
reflecting surfaces each having a curvature and reflecting the
incident light beam in succession, and an emergence surface from
which the light beam reflected by the plurality of reflecting
surfaces is refracted and emerges are integrally formed on the
surface of a transparent member, wherein an optical member such as
an optical filter is adhesively secured to the incidence surface
and/or said emergence surface to thereby make a holding member for
the optical member unnecessary and achieve the simplification of
the entire device, and an optical system using the same.
[0095] Besides this, according to the present invention, there can
be provided an optical system in which a solid state image pickup
element is adhesively secured to an off-axial optical unit, a prism
or the like to thereby effect the positioning of the two and
prevent any positional deviation after the manufacture.
[0096] Also, there can be provided an optical system in which the
respective contact area of the optically effective portion of an
off-axial optical unit, an optical correcting plate and a solid
state image pickup element with air is decreased to thereby reduce
the influence of dust.
* * * * *