U.S. patent application number 11/783797 was filed with the patent office on 2007-11-15 for variable focal length lens system and imaging apparatus.
This patent application is currently assigned to Sony Corporation. Invention is credited to Motoyuki Ohtake.
Application Number | 20070263299 11/783797 |
Document ID | / |
Family ID | 38446001 |
Filed Date | 2007-11-15 |
United States Patent
Application |
20070263299 |
Kind Code |
A1 |
Ohtake; Motoyuki |
November 15, 2007 |
VARIABLE FOCAL LENGTH LENS SYSTEM AND IMAGING APPARATUS
Abstract
A variable focal length lens system includes: a first lens group
having a positive refractive power; a second lens group having a
negative refractive power; a third lens group having a positive
refractive power; and a fourth lens group having a positive
refractive power. As the lens position state changes from a
wide-angle end state to a telephoto end state, at least each of the
lens groups is mobile, the second lens group moves towards the
image side and the third lens group moves towards the object side
such that the gap between the first and the second lens group
increases, and the gap between the second and the third lens group
decreases, while the fourth lens group moves in the direction of
the optical axis so as to compensate for changes in the position of
the image plane which accompany movements of each of the lens
group.
Inventors: |
Ohtake; Motoyuki; (Saitama,
JP) |
Correspondence
Address: |
RADER FISHMAN & GRAUER PLLC
LION BUILDING, 1233 20TH STREET N.W., SUITE 501
WASHINGTON
DC
20036
US
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
38446001 |
Appl. No.: |
11/783797 |
Filed: |
April 12, 2007 |
Current U.S.
Class: |
359/774 |
Current CPC
Class: |
G02B 15/144113 20190801;
G02B 15/173 20130101; G02B 15/145129 20190801 |
Class at
Publication: |
359/774 |
International
Class: |
G02B 9/34 20060101
G02B009/34 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2006 |
JP |
2006-120319 |
Claims
1. A variable focal length lens system, comprising, in order and
from an object side: a first lens group having a positive
refractive power; a second lens group having a negative refractive
power; a third lens group having a positive refractive power; and a
fourth lens group having a positive refractive power, wherein as
the lens position state changes from a wide-angle end state, where
a focal length is shortest, to a telephoto end state, where the
focal length is longest, at least each of the lens groups from the
first lens group through the fourth lens group is mobile, the
second lens group moves towards an image side and the third lens
group moves towards the object side in such a manner that a gap
between the first lens group and the second lens group increases,
and a gap between the second lens group and the third lens group
decreases, while the fourth lens group moves in a direction of an
optical axis so as to compensate for changes in a position of an
image plane which accompany movements of each of the lens group,
the first lens group is closer to the object in the telephoto end
state as compared to the wide-angle end state, the second lens
group includes, in order and from the object side, a negative lens
of a meniscus shape having a concave surface and an aspheric
surface on the image side, and a cemented negative lens of a
bi-concave lens and a positive lens of a meniscus shape and whose
convex surface is turned towards the object, and following
conditional equations (1) and (2) are satisfied:
0.15<f2a/f2b<0.3; and (1) 0.3<D12t/ft<0.45, where (2)
f2a is a focal length of the negative lens placed within the second
lens group, f2b is a focal length of the cemented negative lens
placed within the second lens group, D12t is a gap between the
first lens group and the second lens group in the telephoto end
state, and ft is a focal length of the overall lens system in the
telephoto end state.
2. The variable focal length lens system according to claim 1,
wherein a following conditional equation (3) is satisfied:
0.3<n2P-n2N, where (3) n2N is a refractive index of, with
respect to d-line, the negative lens in the cemented negative lens
within the second lens group, and n2P is a refractive index of,
with respect to the d-line, the positive lens in the cemented
negative lens within the second lens group.
3. The variable focal length lens system according to claim 1,
wherein the fourth lens group moves in the direction of the optical
axis in close-range focusing, and following conditional equations
(4) and (5) are satisfied: -1<.beta.2w<0 (4) .beta.2t<-1,
where (5) .beta.2w is a transverse magnification of the second lens
group in the wide-angle end state, and .beta.2t is a transverse
magnification of the second lens group in the telephoto end
state.
4. The variable focal length lens system according to claim 3,
wherein a following conditional equation (6) is satisfied:
0.17<.DELTA.3/ft<0.25, where (6) .DELTA.3 is an amount of
movement of the third lens group when the lens position state
changes from the wide-angle end state to the telephoto end
state.
5. The variable focal length lens system according to claim 1,
further comprising a fifth lens group on the image side of the
fourth lens group, wherein the fifth lens group includes a negative
parts group having a negative refractive power, and a positive
parts group having a positive refractive power and which is
positioned on the image side of the negative parts group with an
air gap in between.
6. The variable focal length lens system according to claim 5,
wherein the fifth lens group is fixed in the direction of the
optical axis when the lens position state changes.
7. The variable focal length lens system according to claim 6,
wherein the third lens group includes a cemented positive lens,
which is of a positive lens and a negative lens.
8. The variable focal length lens system according to claim 5,
wherein the following conditional equation (7) is satisfied:
0.25<fw/f35w<0.3, where (7) fw is a focal length of the
overall lens system in the wide-angle end state, and f35w is a
combined focal length of the third lens group through the fifth
lens group in the wide-angle end state.
9. The variable focal length lens system according to claim 6,
wherein the following conditional equation (7) is satisfied:
0.25<fw/f35w<0.3, where (7) fw is a focal length of the
overall lens system in the wide-angle end state, and f35w is a
combined focal length of the third lens group through the fifth
lens group in the wide-angle end state.
10. The variable focal length lens system according to claim 7,
wherein the following conditional equation (7) is satisfied:
0.25<fw/f35w<0.3, where (7) fw is a focal length of the
overall lens system in the wide-angle end state, and f35w is a
combined focal length of the third lens group through the fifth
lens group in the wide-angle end state.
11. The variable focal length lens system according to claim 8,
wherein a following conditional equation (8) is satisfied:
0.4<Dsw/TLw<0.55, where (8) Dsw is a distance between a
aperture stop and the image plane in the wide-angle end state, and
TLw is an entire lens length in the wide-angle end state.
12. An imaging apparatus, comprising: a variable focal length lens
system; and an imaging device that converts an optical image formed
by the variable focal length lens system into electric signals,
wherein the variable focal length lens system includes, in order
and from an object side: a first lens group having a positive
refractive power; a second lens group having a negative refractive
power; a third lens group having a positive refractive power; and a
fourth lens group having a positive refractive power, wherein as
the lens position state changes from a wide-angle end state, where
a focal length is shortest, to a telephoto end state, where the
focal length is longest, at least each of the lens groups from the
first lens group through the fourth lens group is mobile, the
second lens group moves towards an image side and the third lens
group moves towards the object side in such a manner that a gap
between the first lens group and the second lens group increases,
and a gap between the second lens group and the third lens group
decreases, while the fourth lens group moves in a direction of an
optical axis so as to compensate for changes in a position of an
image plane which accompany movements of each of the lens group,
the first lens group is closer to the object in the telephoto end
state as compared to the wide-angle end state, the second lens
group includes, in order and from the object side, a negative lens
of a meniscus shape having a concave surface and an aspheric
surface on the image side, and a cemented negative lens of a
bi-concave lens and a positive lens of a meniscus shape and whose
convex surface is turned towards the object, and following
conditional equations (1) and (2) are satisfied:
0.15<f2a/f2b<0.3; and (1) 0.3<D12t/ft<0.45, where (2)
f2a is a focal length of the negative lens placed within the second
lens group, f2b is a focal length of the cemented negative lens
placed within the second lens group, D12t is a gap between the
first lens group and the second lens group in the telephoto end
state, and ft is a focal length of the overall lens system in the
telephoto end state.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present application contains subject matter related to
Japanese Patent Application JP 2006-120319 filed in the Japanese
Patent Office on Apr. 25, 2006, the entire content of which being
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a new variable focal length
lens system and imaging apparatus. More specifically, the present
invention relates to a variable focal length lens system whose zoom
ratio exceeds lOx and that is used in video cameras, digital still
cameras and the like, as well as to an imaging apparatus equipped
with the above-mentioned variable focal length lens system.
[0004] 2. Description of Related Art
[0005] There is known a method of recording a subject image, which
is formed by an imaging device, as a recording means in a camera,
using such photoelectric transducers as CCDs (Charge Coupled
Devices) or CMOSs (Complementary Metal-Oxide Semiconductors) and
formed on the plane of the imaging device, by converting the light
intensity of the subject image into an electric output by way of
each photoelectric transducer.
[0006] Along with the advancement in microfabrication technology in
recent years, central processing units have become faster and
storage media have witnessed higher integration. As a result, it
has become possible to process large volumes of image data, which
could not be handled before, at high speeds. In addition, imaging
devices have become more highly integrated and much smaller, and
higher levels of integration have made recording at higher spatial
frequencies possible, while their smaller sizes have brought about
reductions in the overall size of cameras.
[0007] However, the above-mentioned integration and miniaturization
result in a smaller light reception area for each photoelectric
transducer, thereby causing a drop in the electric output which is
accompanied by an increase in noise. In order to counter this
issue, such attempts as increasing the light intensity that reaches
the imaging device by magnifying the focal ratio of an optical
system or placing small lens elements (referred to as micro lens
arrays) right in front each photoelectric transducer have been
made. While the above-mentioned micro lens arrays do guide beams of
light that fall between adjacent photoelectric transducers onto the
photoelectric transducers, they limit the positioning of the exit
pupil in the lens system. In other words, as the exit pupil in the
lens system approaches the imaging device, that is, as the angle
between the chief ray reaching the imaging device and the optical
axis become greater, off-axis light beams directed towards the
periphery of the screen form greater angles with respect to the
optical axis, and as a result, they do not reach the photoelectric
transducers, and cause insufficient light intensity.
[0008] In recent years, as digital cameras have become more
popular, users' needs have also become more diverse.
[0009] Zoom lenses that have a zoom ratio exceeding I Ox are
capable of capturing a subject in larger sizes. In particular,
since cameras with integrated lenses cannot have their lenses
changed, users of such cameras desire greater zoom ratios even if
it means they have to settle for larger cameras.
[0010] As zoom lenses with zoom ratios exceeding lOx, those, for
example, disclosed in Japanese Patent Application Publication Nos.
2005-215385 (Patent Document 1), 2003-295059 (Patent Document 2),
2005-128186 (Patent Document 3) and the like are known.
[0011] The zoom lenses disclosed in Patent Document 1 and Patent
Document 2 include four lens groups, which are, in order and from
the side of the object, a first lens group having a positive
refractive power, a second lens group having a negative refractive
power, a third lens group having a positive refractive power, and a
fourth lens group having a positive refractive power. The four lens
groups are so configured that when the lens position state changes
from a wide-angle end state to a telephoto end state, the first
lens group moves towards the object, the second lens group moves
towards the image, the third lens group moves towards the image
after first moving towards the object, and the fourth lens groups
moves towards the image after first moving towards the object. In
addition, the zoom lens disclosed in Patent Document 1 is so
configured that an aperture stop placed between the second lens
group and the third lens group moves independently of the other
lens groups.
[0012] The zoom lens disclosed in Patent Document 3 includes four
lens groups, a first lens group having a positive refractive power,
a second lens group having a negative refractive power, a third
lens group having a positive refractive power, and a fourth lens
group having a positive refractive power. These lens groups are so
configured that when the lens position state changes from the
wide-angle end state to the telephoto end state, the first lens
group and the third lens group are fixed in the direction of the
optical axis, the second lens group moves towards the image, and
the fourth lens group moves so as to compensate for changes in the
position of the plane of the image that accompany the movement of
the second lens group.
SUMMARY OF THE INVENTION
[0013] However, there is an issue with the above-mentioned zoom
lenses of related art in that, since the zooming function centers
on the second lens group, performance is compromised if the second
lens group is misaligned even by the smallest amount at the time of
manufacture.
[0014] In the zoom lens disclosed in the above-mentioned Patent
Document 1, the second lens group includes three single lenses.
Since the positive spherical aberration that occurs at the second
lens group is corrected by the image-side lens surface of a second
negative lens of the second lens group and the object-side lens
surface of a positive lens located on the image-side of the
above-mentioned negative lens, performance is easily compromised if
the above-mentioned two lens surfaces are misaligned.
[0015] The second lens group of the zoom lenses disclosed in Patent
Document 2 and Patent Document 3 includes, in order and from the
side of the object, a first negative lens, a second negative lens,
and a cemented lens of a positive lens and a negative lens. As a
result, it is possible to weaken the refractive power of the
image-side lens surface of the second negative lens, thereby
reducing performance degradation caused by a misalignment between
the second negative lens and the cemented lens.
[0016] However, in the zoom lenses disclosed in Patent Document 2
and Patent Document 3, there is an issue in that the diameter of
the first lens group becomes bigger due to the fact that there are
many lenses in the second lens group which causes the second lens
group to be thicker.
[0017] Accordingly, it is desirable to provide a variable focal
length lens system that achieves a high zoom ratio as well as
miniaturization, and an imaging apparatus using such a variable
focal length lens system. The present invention addresses the
issues above.
[0018] A variable focal length lens system according to an
embodiment of the present invention includes, in order and from the
side of the object, a first lens group having a positive refractive
power, a second lens group having a negative refractive power, a
third lens group having a positive refractive power, and a fourth
lens group having a positive refractive power. When the lens
position state changes from a wide-angle end state, where the focal
length is shortest, to a telephoto end state, where the focal
length is greatest, at least each of the lens groups from the
above-mentioned first lens group to the above-mentioned fourth lens
group is mobile, and the above-mentioned second lens group moves
towards the image while the above-mentioned third lens group moves
towards the object so that the gap between the above-mentioned
first lens group and the above-mentioned second lens group grows
bigger, while the gap between the above-mentioned second lens group
and the above-mentioned third lens group becomes smaller. At the
same time, the above-mentioned fourth lens group moves in the
direction of the optical axis in order to compensate for the change
in the position of the plane of the image that accompanies the
movement of each of the lens groups. The above-mentioned first lens
group is positioned closer to the object in the telephoto end state
as compared to the wide-angle end state. The second lens group
includes, in order and from the side of the object, a negative
lens, which is of a meniscus shape and which has a concave surface
and an aspherical surface on the image side, and a cemented
negative lens, which is of a biconcave lens and a positive lens of
a meniscus shape that has its convex surface facing the object.
Assuming f2a is the focal length of the negative lens placed in the
second lens group, f2B the focal length of the cemented negative
lens placed in the second lens group, D12t the distance between the
first lens group and the second lens group in the telephoto end
state, and ft the focal length of the overall lens system in the
telephoto end state, the following conditional equations hold
true:
0.15<f2a/f2b<0.3, and (1)
0.3<D12t/ft<0.45. (2)
[0019] In addition, an imaging apparatus according to an embodiment
of the present invention includes a variable focal length lens
system, and an imaging device which converts an optical image
formed by the above-mentioned variable focal length lens system
into electric signals. The above-mentioned variable focal length
lens system includes, in order and from the side of the object, a
first lens group having a positive refractive power, a second lens
group having a negative refractive power, a third lens group having
a positive refractive power, and a fourth lens group having a
positive refractive power. When the lens position state changes
from a wide-angle end state, where the focal length is shortest, to
a telephoto end state, where the focal length is greatest, at least
each of the lens groups from the above-mentioned first lens group
to the above-mentioned fourth lens group is mobile, and the
above-mentioned second lens group moves towards the image while the
above-mentioned third lens group moves towards the object so that
the gap between the above-mentioned first lens group and the
above-mentioned second lens group grows bigger, while the gap
between the above-mentioned second lens group and the
above-mentioned third lens group becomes smaller. At the same time,
the above-mentioned fourth lens group moves in the direction of the
optical axis in order to compensate for the change in the position
of the plane of the image that accompanies the movement of each of
the lens groups. The above-mentioned first lens group is positioned
closer to the object in the telephoto end state as compared to the
wide-angle end state. The second lens group includes, in order and
from the side of the object, a negative lens, which is of a
meniscus shape and which has a concave surface and an aspherical
surface on the image side, and a cemented negative lens, which is
of a biconcave lens and a positive lens of a meniscus shape that
has its convex surface facing the object. In addition, the
following conditional equations hold true: (1)
0.15<f2a/f2b<0.3, and (2) 0.3<D12t/ft<0.45.
[0020] According to the present invention, a high zoom ratio and
miniaturization may be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic diagram illustrating the allocation of
refractive power and the state of movement in relation to zooming
in several embodiments of a variable focal length lens system of
the present invention;
[0022] FIG. 2 illustrates the lens configuration for an embodiment
of a variable focal length lens system according to the present
invention;
[0023] FIG. 3, along with FIGS. 4 through 7, shows various
aberration graphs with respect to a numerical embodiment in which
specific values are applied to an embodiment of a variable focal
length lens system of the present invention, and the graphs in FIG.
3 illustrate the spherical aberration, astigmatism, distortion and
transverse aberration in a wide-angle end state;
[0024] FIG. 4 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a first mid-focal length
state;
[0025] FIG. 5 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a second mid-focal length
state;
[0026] FIG. 6 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a third mid-focal length
state;
[0027] FIG. 7 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a telephoto end state;
[0028] FIG. 8 illustrates the lens configuration for another
embodiment of a variable focal length lens system according to the
present invention;
[0029] FIG. 9, along with FIGS. 10 through 13, shows various
aberration graphs with respect to another numerical embodiment in
which specific values are applied to the variable focal length lens
system shown in FIG. 8, and the graphs in FIG. 9 illustrate the
spherical aberration, astigmatism, distortion and transverse
aberration in a wide-angle end state;
[0030] FIG. 10 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a first mid-focal length
state;
[0031] FIG. 11 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a second mid-focal length
state;
[0032] FIG. 12 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a third mid-focal length
state;
[0033] FIG. 13 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a telephoto end state;
[0034] FIG. 14 illustrates the lens configuration for another
embodiment of a variable focal length lens system according to the
present invention;
[0035] FIG. 15, along with FIGS. 16 through 19, shows various
aberration graphs with respect to another numerical embodiment in
which specific values are applied to the variable focal length lens
system shown in FIG. 14, and the graphs in FIG. 15 illustrate the
spherical aberration, astigmatism, distortion and transverse
aberration in a wide-angle end state;
[0036] FIG. 16 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a first mid-focal length
state;
[0037] FIG. 17 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a second mid-focal length
state;
[0038] FIG. 18 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a third mid-focal length
state;
[0039] FIG. 19 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a telephoto end state;
[0040] FIG. 20 illustrates the lens configuration for another
embodiment of a variable focal length lens system according to the
present invention;
[0041] FIG. 21, along with FIGS. 22 through 25, shows various
aberration graphs with respect to another numerical embodiment in
which specific values are applied to the variable focal length lens
system shown in FIG. 20, and the graphs in FIG. 21 illustrate the
spherical aberration, astigmatism, distortion and transverse
aberration in a wide-angle end state;
[0042] FIG. 22 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a first mid-focal length
state;
[0043] FIG. 23 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a second mid-focal length
state;
[0044] FIG. 24 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a third mid-focal length
state;
[0045] FIG. 25 illustrates the spherical aberration, astigmatism,
distortion and transverse aberration in a telephoto end state;
[0046] FIG. 26 is a schematic diagram illustrating the allocation
of refractive power and the state of movement in relation to
zooming in another embodiment of a variable focal length lens
system of the present invention; and
[0047] FIG. 27 is a block diagram illustrating an embodiment of an
imaging apparatus of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0048] Hereinbelow, embodiments of a variable focal length lens
system and imaging apparatus of the present invention are
described.
[0049] A variable focal length lens system according to an
embodiment of the present invention may include, in order and from
the side of the object, a first lens group having a positive
refractive power, a second lens group having a negative refractive
power, a third lens group having a positive refractive power, and a
fourth lens group having a positive refractive power. When the lens
position state changes from a wide-angle end state, where the focal
length is shortest, to a telephoto end state, where the focal
length is greatest, at least each of the lens groups from the
above-mentioned first lens group to the above-mentioned fourth lens
group is mobile, and the above-mentioned second lens group moves
towards the image while the above-mentioned third lens group moves
towards the object so that the gap between the above-mentioned
first lens group and the above-mentioned second lens group grows
bigger, while the gap between the above-mentioned second lens group
and the above-mentioned third lens group becomes smaller. At the
same time, the above-mentioned fourth lens group moves in the
direction of the optical axis in order to compensate for the change
in the position of the plane of the image that accompanies the
movement of each of the lens groups. The above-mentioned first lens
group is positioned closer to the object in the telephoto end state
as compared to the wide-angle end state. The second lens group may
include, in order and from the side of the object, a negative lens,
which is of a meniscus shape and which has a concave surface and an
aspherical surface on the image side, and a cemented negative lens,
which is of a biconcave lens and a positive lens of a meniscus
shape that has its convex surface facing the object. The
conditional equations (1) 0.1521 f2a/f2b <0.3, and (2)
0.3<D12t/ft<0.45 are satisfied, where f2a is the focal length
of the negative lens placed in the second lens group, f2b is the
focal length of the cemented negative lens placed in the second
lens group, D12t is the distance between the first lens group and
the second lens group in the telephoto end state, and ft is the
focal length of the overall lens system in the telephoto end
state.
[0050] Therefore, according to a variable focal length lens system
of the present embodiment, both a high zoom ratio and
miniaturization can be achieved simultaneously.
[0051] In a variable focal length lens system of the present
embodiment, in order to achieve both a high zoom ratio and
miniaturization with the configuration described above, attention
is given to decreasing the load placed on the second lens group in
changing the lens position state, and, in order to secure stable
optical qualities at the manufacturing stage, to simplifying the
configuration of the second lens group.
[0052] Here, what is meant by decreasing the load placed on the
second lens group in changing the lens position state is
suppressing the change in the transverse magnification of the
second lens group.
[0053] Assuming that .phi.1 is the refractive power of the first
lens group, .phi.2 the refractive power of the second lens group,
Dw the gap between the principal points of the first lens group and
the second lens group in the wide-angle end state, and Dt the gap
between principal points of the first lens group and the second
lens group in the telephoto end state, the combined refractive
power at the wide-angle end state .phi.12w and the combined
refractive power at the telephoto end state .phi.12t may be
expressed as follows:
.phi.12w=.phi.1+.phi.2-.phi.1.phi.2Dw
.phi.12t=.phi.1+.phi.2-.phi.1.phi.2Dt,
while the transverse magnification .beta.2w and .beta.2t of the
second lens group in the wide-angle end state and the telephoto end
state, respectively, may be expressed as follows:
.beta.2w=.phi.1/.phi.12w
whose convex surface faces the object side, where the cemented lens
is placed on the image side of the negative lens with an air gap in
between, factors that may contribute to misalignment that occur
during incorporation into the lens chamber at the manufacturing
stage are reduced, and stable optical qualities are thereby
realized.
[0054] In particular, with respect to a variable focal length lens
system of the present embodiment, by clarifying the aberration
correction functions that each of the two lens components
configuring the second lens group is to serve, better performance
is achieved, and by reducing the effect of assembly errors at the
manufacturing stage, stable optical qualities are realized.
[0055] More specifically, the negative lens positioned closer to
the object has an aspherical surface and mainly plays the role of
correcting fluctuations in coma aberration that accompany changes
in the angle of field, and the cemented negative lens positioned
closer to the image plays mainly the role of correcting axial
aberration. By causing negative spherical aberration with the
cemented surfaces, the above-mentioned cemented negative lens is
capable of correcting axial aberration.
[0056] It is noted that while the above-mentioned cemented negative
lens may be separated into two lens elements, namely a negative
lens and a positive lens, when they are separated as such, there
arises a need to sufficiently suppress performance degradation that
may be caused by any misalignment between the negative lens and the
positive lens. This is because positive spherical aberration is
caused by the lens surface on the image side of the negative lens,
negative spherical aberration is caused by the lens surface on the
object side of the positive lens, and they are made to cancel each
other out.
[0057] By sufficiently widening the gap between the negative lens
and the positive lens, it is possible to weaken the refractive
power and thereby suppress performance degradation, but this causes
the lens diameter to become bigger. In addition, since
.beta.2t=.phi.1/.phi.12t,
and therefore, the change in transverse magnification
.beta.2t/.beta.2w may be expressed as follows:
.beta. 2 t / .beta. 2 w = .phi. 12 w / .phi. 12 t = ( .phi.1 +
.phi.2 - .phi.1 .phi.2 Dw ) / ( .phi.1 + .phi.2 - .phi.1 .phi.2 Dt
) ##EQU00001##
Since .phi.1>0, and .phi.2<0, .phi.1+.phi.2 is relatively
small, and as a result, the change in the transverse magnification
of the second lens group is dependent upon the amount of change in
the gap between the first lens group and the second lens group,
namely, (Dw-Dt).
[0058] In a variable focal length lens system of the present
embodiment, by decreasing (Dw-Dt), which is the amount of change in
the gap between the first lens group and the second lens group, the
load placed on the second lens group in zooming is reduced, and the
occurrence of off-axis aberrations caused by the second lens group
in connection with the change in the lens position state is
suppressed, thereby achieving better performance.
[0059] With respect to a variable focal length lens system of the
present embodiment, what is meant by simplifying the configuration
of the second lens group is configuring the second lens group with
two negative lens components (here, "one lens component" refers to
a single lens or one cemented lens).
[0060] When the second lens group includes three or more lens
components, factors that may contribute to misalignment which occur
when the lenses are incorporated into the lens chamber at the
manufacturing state increase, and it thus becomes difficult to
secure stable optical qualities.
[0061] In a variable focal length lens system of the present
embodiment, by configuring the second lens group with a negative
lens, which has a meniscus shape, a concave surface facing the
image side, and an aspherical surface image side, and a cemented
negative lens, which has a negative biconcave lens and a positive
lens the second lens group becomes thicker, it becomes impossible
to secure a sufficient amount of movement for the second lens
group.
[0062] As mentioned above, with respect to a variable focal length
lens system of the present embodiment, by simplifying the
configuration of the second lens group, the second lens group
becomes thinner, and it is thereby possible to reduce the lens
diameter of the first lens group.
[0063] With respect to a variable focal length lens system of the
present embodiment, by moving the first lens group closer towards
the object side in the telephoto end state as compared to the
wide-angle end state, the off-axis light beam that is incident upon
the first lens group in the wide-angle end state is brought closer
to the optical axis, and coma aberration that occurs in the
periphery of the screen is thus well corrected for.
[0064] In addition, when the lens position state changes from the
wide-angle end state to the telephoto end state, by moving the
third lens group towards the object, the change in the transverse
magnification of the third lens group that accompanies the change
in the lens position state is increased, and the reduction in the
change of the transverse magnification of the second lens group is
thus compensated for.
[0065] By configuring a variable focal length lens system of the
present embodiment in the manner described above while satisfying
conditional equations (1) and (2), a higher zoom ratio and a
smaller lens diameter can be achieved simultaneously.
0.15<f2a/f2b<0.3 Conditional Equation (1)
Conditional equation (1) is a conditional equation that defines the
focal length of the above-mentioned cemented negative lens, and is
a conditional equation that is necessary in order to simplify the
configuration of the second lens group.
[0066] When the upper limit value of conditional equation (1) is
exceeded (i.e. the refractive power of the cemented negative lens
becomes stronger), it becomes impossible to correct the positive
spherical aberration that occurs with respect to the cemented
negative lens alone, and as a result, it becomes difficult to
obtain the desired optical performance.
[0067] On the contrary, when the lower limit value of conditional
equation (1) is not satisfied (i.e. the refractive power of the
negative lens becomes stronger), the change, which accompanies the
change in the lens position state, in the height of the off-axis
light beam that passes through the negative lens becomes smaller.
As a result, it becomes difficult to correct the change in off-axis
aberration that accompanies the change in the lens position
state.
0.3<D12t/ft<0.45 Conditional Equation (2)
[0068] As described above, with a variable focal length lens system
of the present embodiment, the amount of change in the gap between
the first lens group and the second lens group, which accompanies
the change in the lens position state, is made smaller. In the
wide-angle end state, since the first lens group and the second
lens group are placed in close proximity to each other, the
above-mentioned amount of change in the gap is approximately
comparable to the gap between the first lens group and the second
lens group in the telephoto end state.
[0069] In addition, if Z (=ft/fw) is taken to be the zoom ratio,
then D12t/ft=D12t/(fwZ). Since fw serves to normalize at the focal
length for the wide-angle end state, conditional equation (2)
defines the value which is obtained by dividing the amount of
change in the gap between the first lens group and ,the second lens
group by the zoom ratio.
[0070] When the upper limit value for conditional equation (2) is
exceeded, the range of the transverse magnification of the second
lens group becomes greater. Therefore, when the configuration of
the second lens group is simplified, fluctuations in the off-axis
aberration which accompany the change in the lens position state
become more significant, and it thus becomes difficult to obtain
the desired optical performance.
[0071] On the contrary, when the lower limit value for conditional
equation (2) is not satisfied, the range of the transverse
magnification of the second lens group becomes smaller. However,
the load placed upon the other lens groups becomes too big, and it
thus becomes difficult to obtain the desired optical
performance.
[0072] According to an embodiment of a variable focal length lens
system of the present invention, in order to better correct for the
on-axis aberration that occurs due to the cemented negative lens in
the second lens group and to further improve performance, it is
desirable that conditional equation (3) shown below be satisfied,
where n2N is the refractive index of, with respect to the d-line,
the negative lens of the cemented negative lens placed in the
second lens group, and n2P is the refractive index of, with respect
to the d-line, the positive lens of the cemented negative lens
placed in the second lens group:
0.3<n2P-n2N (3)
[0073] Conditional equation (3) defines the negative spherical
aberration that occurs at the cemented surfaces within the cemented
negative lens.
[0074] When the lower limit value of conditional equation (3) is
not satisfied, the difference in refractive index between the two
lenses that configure the cemented negative lens becomes smaller.
As a result, there is no choice but to reduce the radius of
curvature of the cemented surfaces, causing the occurrence of a
high order spherical aberration and making it difficult to obtain
the desired optical performance, and at the same time the second
lens group becomes thicker.
[0075] According to an embodiment of a variable focal length lens
system of the present invention, during close-range focusing, it is
desirable that the fourth lens group move in the direction of the
optical axis, and conditional equations (4) and (5) shown below be
satisfied, where .beta.2w is the transverse magnification of the
second lens group in the wide-angle end state, and .beta.2t is the
transverse magnification of the second lens group in the telephoto
end state:
-1<.beta.2w<0 (4)
.beta.2t<-1 (5)
[0076] Generally, in a zoom lens, close-range focusing is performed
by moving one of the lens groups making up the zoom lens in the
direction of the optical axis. In a zoom lens whose first lens
group has a positive refractive power, since the lens diameter of
the first lens group is big, if close-range focusing is to be
performed by moving the first lens group, the drive system has to
be bigger in size, causing the lens tube diameter to become
bigger.
[0077] In particular, as auto-focusing functions have become
popular, faster operation speeds have been desired. In order to
increase operation speed, it would be effective to reduce the
amount of work (=weight.times.distance) that needs to be performed
during auto-focusing, and a method of performing close-range
focusing by moving a lens group that is positioned closer to the
image than is the first lens group would therefore be suitable to
this end.
[0078] However, in a positive-negative-positive-positive four-group
zoom lens, when a position where the transverse magnification
.beta.2 of the second lens group is x-1 and is held while changing
the lens position state from the wide-angle end state to the
telephoto end state, it is difficult to perform close-range
focusing by way of the second lens group. This is because when the
position is such that .beta.2=-1, it is impossible to perform
close-range focusing, and the direction of movement for the range
-1<.beta.2<0 is the opposite of that for the range
.beta.2<-1.
[0079] As described above, by performing close-range focusing by
moving the fourth lens group, transverse magnification .beta.2 of
the second lens group becomes free. As a result, it becomes
possible to weaken the refractive power of the second lens group,
the degree of freedom in correcting for aberrations is enhanced,
and further improvements in performance can be expected.
[0080] Conditional equations (4) and (5) signify that, by
performing close-range focusing through the fourth lens group,
restrictions on the transverse magnification of the second lens
group disappear, and the degree of freedom in correcting for
aberrations is enhanced.
[0081] In addition, when the lens position state changes from the
wide-angle end state to the telephoto end state, the fourth lens
group first moves towards the object while the transverse
magnification of the second lens group is between -1 and 0, and the
fourth lens group moves towards the image once the transverse
magnification of the second lens group becomes smaller than -1.
[0082] With respect to a subject that is at a predetermined
distance, the distance to be covered in order to perform
close-range focusing is greater in the telephoto end state as
compared to the wide-angle end state. As described above, by having
the fourth lens group move, since the gap between the third lens
group and the fourth lens group in the telephoto end state is
sufficiently widened, it is possible to secure enough space for
movement that is required for close-range focusing in the telephoto
end state.
[0083] In a variable focal length lens system of the present
embodiment, as described above, by decreasing the load placed on
the second lens group in zooming, the configuration of the second
lens group is simplified, but in order to maintain a predetermined
zoom ratio, a lens group that is to compensate for the load related
to zooming that is taken away from the second lens group is
necessary.
[0084] As such, in a variable focal length lens system of the
present embodiment, in relation to the fact that the contribution
that the second lens group makes in zooming is decreased, the third
lens group partially shoulders the load related to zooming by
moving the third lens group towards the object in changing the lens
position state from the wide-angle end state to the telephoto end
state.
[0085] In an embodiment of a variable focal length lens system of
the present invention, in order to further improve performance, it
is desirable that conditional equation (6) shown below be
satisfied, where .DELTA.3 is the amount of movement of the third
lens group when the lens position state changes from the wide-angle
end state to the telephoto end state:
0.17<.DELTA.3/ft<0.25 (6)
[0086] Conditional equation (6) defines the proportion of zooming
that the third lens group is responsible for, and defines the
fluctuation in on-axis aberration that occurs when the lens
position state is varied.
[0087] When the upper limit value of conditional equation (6) is
exceeded, the proportion of zooming that the third lens group is
responsible for becomes greater. In other words, the transverse
magnification of the third lens group varies to a greater extent.
As a result, the fluctuation in on-axis aberration that occurs due
to the third lens group when the lens position state changes
becomes greater, and it thus becomes difficult to achieve better
performance and greater zoom ratios.
[0088] When the lower limit value of conditional equation (6) is
not satisfied, the transverse magnification of the fourth lens
group varies to a greater extent, causing the amount of movement of
the fourth lens group to increase significantly particularly in the
telephoto end state, and it thus causes the drive mechanism that
performs close-range focusing to become more complex.
[0089] In an embodiment of a variable focal length lens system of
the present invention, it is desirable to provide a fifth lens
group on the image side of the fourth lens group, and it is
desirable to have the fifth lens group configured with a negative
parts group having a negative refractive power, and a positive
parts group having a positive refractive power that is positioned
on the image side of the above-mentioned negative parts group with
an air gap in between.
[0090] The fifth lens group performs the functions described
below.
[0091] One is the function of adjusting the exit pupil position. By
providing the negative parts group having a negative refractive
power and the positive parts group having a positive refractive
power on the image side of the negative parts group with an air gap
in between, the exit pupil position is distanced from the plane of
the image. In other words, it becomes possible for the principal
ray to reach the image plane position in a state where it is almost
parallel to the optical axis.
[0092] The other function is that of correcting for distortion. By
positioning the negative parts group having a negative refractive
power in such a manner that the lens surface on the image side has
a strong concave surface facing the image side, it becomes possible
to correct for negative distortion that is likely to occur in the
wide-angle end state.
[0093] In an embodiment of a variable focal length lens system of
the present invention, by having the above-mentioned fifth lens
group fixed in the direction of the optical axis when the lens
position state is varied, it is possible to simplify, the structure
of the lens tube.
[0094] In a variable focal length lens system according to an
embodiment of the present invention equipped with the fifth lens
group, it is desirable that the third lens group be configured with
a cemented positive lens of a positive lens and a negative
lens.
[0095] In a positive-negative-positive-positive four-group zoom
lens of related art, since there is only one lens group that has a
negative refractive-power, negative distortion that is likely to
occur in the wide-angle end state was corrected for by configuring
the third lens group with a positive parts group having a positive
refractive power and a negative parts group having a negative
refractive power. As described above, by providing the fifth lens
group, it is possible to correct for negative distortion by way of
the fifth lens group. As a result, it becomes unnecessary to
configure the third lens group with a positive parts group and a
negative parts group.
[0096] However, as described above, since the third lens group is
partially responsible for zooming, in order to correct for the
spherical aberration that occurs in association with the change in
the lens position state or in order to correct for chromatic
aberration, a configuration using a cemented positive lens of a
positive lens and a negative lens is desirable, and by adopting
such a configuration, further enhancement of performance can be
achieved.
[0097] In addition, in achieving smaller lens diameters, the
positioning of the aperture stop is also important.
[0098] In general, when the aperture stop is positioned closer to
the center of the optical system, it is possible to make the lens
diameter of each of the lens groups smaller.
[0099] In a variable focal length lens system according to an
embodiment of the present invention, the lens diameter is made
smaller by positioning an aperture stop between the second lens
group and the third lens group which brings the height of the
off-axis luminous flux that is incident upon the first lens group
closer to the optical axis in the wide-angle end state. In
addition, by positioning the first lens group and the second lens
group in proximity to each other, the off-axis luminous flux that
passes through the second lens group in the wide-angle end state
can be changed actively in accordance with the change in the angle
of field, and fluctuations in coma aberration that accompany
changes in the angle of field can thus be well corrected for.
[0100] In addition, with this configuration, where the aperture
stop is positioned between the second lens group and the third lens
group, by appropriately setting the focal lengths of the lens
groups placed on the image side of the aperture stop (these lens
groups will hereinafter be referred to as "latter groups"), it
becomes possible to further miniaturize the first lens group.
[0101] In order to increase the zoom ratio to extreme extents, it
is also necessary to widen the angle of field in the wide-angle end
state.
[0102] The longer the focal length is in the telephoto end state,
the bigger a subject can be photographed by getting closer to the
subject. However, there is an issue in that the overall length of
the lens becomes longer. With respect to a camera with a built-in
lens, since the lens cannot be changed, it is unsuitable for indoor
shooting unless a wide-conversion lens or the like is attached.
[0103] In a variable focal length lens system according to an
embodiment of the present invention, in achieving a higher zoom
ratio, attention is given to the fact that indoor shooting can be
performed adequately without a conversion lens by widening the
angle of field in the wide-angle end state.
[0104] In general, in order to achieve wider angles, because the
angle of field becomes wider, the off-axis luminous flux that is
incident upon the first lens group moves away from the optical
axis. In other words, the lens diameter of the first lens group
becomes greater.
[0105] In a variable focal length lens system according to an
embodiment of the present invention, as a method of bringing the
height at which the off-axis luminous flux is incident upon the
first lens group closer to the optical axis, attention is given to
reducing the angle formed between the off-axis luminous flux and
the optical axis at the aperture stop position. For this reason,
the aperture stop is positioned between the second lens group and
the third lens group, and the aperture stop moves so as to narrow
the gap between the second lens group and the aperture stop as the
lens position state changes from the wide-angle end state to the
telephoto end state.
[0106] In related art, in recording the image of a subject by an
imaging device, the exit pupil position is distanced from the image
plane so as to prevent shading by a micro lens array. In other
words, it is almost an image side telecentric optical system.
[0107] In an image side telecentric optical system, the exit pupil
is positioned at infinity, that is, it is characteristic in that
the principal ray emerging from the optical system is parallel with
the optical axis. In other words, the aperture stop is positioned
at the object side focal position of the partial optical system
(latter group) positioned on the image side of the aperture
stop.
[0108] For this reason, the longer the focal length of the partial
optical system (latter group) on the image side of the aperture
stop is, the smaller the angle formed between the off-axis luminous
flux and the optical axis at the aperture stop position can be
made.
[0109] As such, in a variable focal length lens system according to
an embodiment of the present invention, by extending the focal
length of the latter group, the effective aperture of the first
lens group is prevented from becoming large even when the angle of
view is widened.
[0110] Therefore, in a variable focal length lens system according
to an embodiment of the present invention, in order to reduce the
lens diameter, assuming fw is the focal length of the overall lens
system in the wide-angle end state, and that f35w is the combined
focal length of the third lens group through the fifth lens group
in the wide-angle end state, it is desirable that conditional
equation (7) shown below be satisfied:
0.25<fw/f35w<0.3 (7)
[0111] When the upper limit value of conditional equation (7) is
exceeded, since the focal length of the latter group becomes
shorter, the angle formed between the principal ray and the optical
axis at the aperture stop position becomes bigger. As a result, the
off-axis luminous flux that is incident upon the first lens group
in the wide-angle end state moves away from the optical axis, and
it becomes difficult to achieve a sufficient reduction in the lens
diameter.
[0112] When the lower limit value of conditional equation (7) is
not satisfied, the gap between the second lens group and the third
lens group required in the wide-angle end state in order to
maintain the focal length in the wide-angle end state becomes
extremely large, and it becomes difficult to reduce the overall
length of the lens.
[0113] With a variable focal length lens system according to an
embodiment of the present invention, in order to achieve a balance
between a reduction in. the lens diameter and better performance,
assuming Dsw is the distance between the aperture stop and the
image plane in the wide-angle end state, and that TLw is the
overall length of the lens in the wide-angle end state, it is
desirable that conditional equation (8) shown below be
satisfied:
0.4<Dsw/TLw<0.55 (8)
[0114] Conditional equation (8) defines the position of the
aperture stop in the wide-angle end state.
[0115] When the lower limit value of conditional equation (8) is
not satisfied, the position of.the aperture stop in the wide-angle
end state moves towards the image plane. Thus, the off-axis
luminous flux passing through the first lens group moves away from
the optical axis, and it becomes difficult to achieve a further
reduction in the lens diameter.
[0116] On the other hand, when the upper limit value of conditional
equation (8) is exceeded, the distance between the aperture stop
and the second lens group becomes shorter. Thus, the refractive
power of the second lens group becomes too strong, and as a result,
it becomes difficult to correct for fluctuations in coma aberration
that accompany changes in the angle of field, and further
improvements in performance become difficult to achieve.
[0117] With a variable focal length lens system according to an
embodiment of the present invention, by having the aperture stop
and the third lens group move together, it is possible to simplify
the structure of the lens tube.
[0118] With respect to a variable focal length lens system
according to an embodiment of the present invention, in order to
further improve performance, it is preferable that the first lens
group include three lenses, which are, in order and from the side
of the object, a cemented lens, which is of a negative lens and a
positive lens, and a positive lens.
[0119] Since the on-axis luminous flux is incident upon the first
lens group with a wide luminous flux diameter in the telephoto end
state, it is likely to give rise to negative spherical aberration.
In addition, since the off-axis luminous flux is distanced from the
optical axis when it is incident, off-axis aberration is likely to
occur.
[0120] By placing the cemented lens of a negative lens and a
positive lens on the side of the first lens group that is closest
to the object, negative spherical aberration and on-axis chromatic
aberration are well corrected for. The positive lens placed on the
image side of the above-mentioned cemented lens mainly corrects for
fluctuations in coma aberration that accompany changes in the angle
of field. By clarifying the function of each lens, it is possible
to achieve better optical performance.
[0121] With a variable focal length lens system according to an
embodiment of the present invention, in order to correct for
fluctuations in various aberrations that occur as the position of a
subject changes, it is desirable that the fourth lens group
include, in order and from the side of the object, a positive lens
whose convex surface faces the image, and a negative lens whose
concave surface faces the object.
[0122] By adopting a doublet configuration, it becomes possible to
correct for both off-axis and on-axis aberrations at the same time,
and fluctuations in various aberrations that occur when the
position of the subject changes can thus be well corrected for.
[0123] With a variable focal length lens system according to an
embodiment of the present invention, in order to better suppress
chromatic aberration, it is desirable that a glass material having
high anomalous dispersion properties be used for the first lens
group.
[0124] In particular, of the lenses that make up the first lens
group, by having the positive lens in the cemented lens be of a
glass material having high anomalous dispersion properties, it is
possible to well correct for secondary dispersion that occurs in
the center portion of the screen in the telephoto end state.
[0125] With a variable focal length lens system according to each
embodiment of the present invention, by employing an aspherical
lens, it is possible to realize better optical performance. In
particular, by introducing an aspherical surface into the fifth
lens group, it becomes possible to further enhance central
performance.
[0126] Further, even better optical performance can also be
achieved by employing a plurality of aspherical surfaces.
[0127] In addition, with a variable focal length lens system
according to each embodiment of the present invention, it is
possible to shift the image by shifting, as a shift lens group, one
lens group of the constituent lens groups or a group of parts
within one lens group in a direction that is almost perpendicular
to the optical axis. Further, by combining a drive system with a
detection system that detects movements of the camera that cause
blurring, and a computation system that computes the amount of
correction in accordance with the output from the detection system,
where the drive system shifts the above-mentioned shift lens group
in accordance with the output from the computation system, it is
possible to have it function as an image stabilizing optical
system.
[0128] With variable focal length lens systems of each of the
configurations described above, it is desirable to have, in
particular, either the third lens group or the positive parts group
in the fifth lens group function as the shift lens group.
[0129] This is because the third lens group is positioned close to
the aperture stop, the off-axis luminous flux passes through a
position close to the optical axis, and fluctuations in off-axis
aberration, when the lens group is shifted, are small. In addition,
this is because, with respect to the positive parts group in the
fifth lens group, the exit pupil is far from the position of the
image plane, and fluctuations in off-axis aberration that occur
when the positive parts group is shifted are small.
[0130] Next, specific embodiments of a zoom lens of the present
invention and numerical embodiments in which actual numerical
values are applied to the above-mentioned specific embodiments will
be described with reference to drawings and tables.
[0131] It is noted that an aspherical surface is introduced in each
of the embodiments, and the shape of the above-mentioned aspherical
surface is to be defined by equation 1 shown below, where x is the
sag amount, y the height from the optical axis, c the curvature, K
the conic constant, A, B, C and D the fourth-, sixth-, eighth- and
tenth-order, respectively, aspherical coefficients, and where the
direction in which light travels is taken to be the positive
direction.
x=cy.sup.2/(1+(1-(1+.kappa.)c.sup.2y.sup.2).sup.1/2)+Ay.sup.4+By.sup.6+.
. . [Equation 1]
[0132] FIG. 1 illustrates the allocation of refractive power with
respect to a variable focal length lens system according to first
through fourth embodiments of the present invention and this
variable focal length lens system includes, in order and from the
side of the object: a first lens group G1 having a positive
refractive power, a second lens group G2 having a negative
refractive power, a third lens group G3 having a positive
refractive power, a fourth lens group G4 having a positive
refractive power, and a fifth lens group G5 having a positive
refractive power. In zooming from a wide-angle end state (the state
shown on the upper side) to a telephoto end state (the state shown
on the lower side), the first lens group through the fourth lens
group move along an optical axis x as indicated with the arrow in
such a manner that the air gap between the first lens group G1 and
the second lens group G2 widens, while the air gap between the
second lens group G2 and the third lens group G3 narrows. In other
words, after first moving towards the image, the first lens group
GI then moves towards the object, while the second lens group G2
moves towards the image, the third lens group G3 moves towards the
object, the fifth lens group is stationary, and the fourth lens
group G4 moves so as to correct for changes in the position of the
image plane that occur in association with the movements of each
lens group while it also moves towards the object during
close-range focusing.
[0133] FIG. 2 illustrates the lens configuration of first
embodiment 1 of a variable focal length lens system of the present
invention. The first lens group G1 includes, in order and from the
side of the object, a cemented lens L11, which is of a negative
lens having a meniscus shape and whose convex surface is turned
towards the object and a positive lens whose convex surface is
turned towards the object, as well as a positive lens L12 whose
convex surface is turned towards the object. The second lens group
G2 includes, in order and from the side of the object, a negative
lens L21 of a meniscus shape that has an aspherical surface on the
image side and whose concave surface is turned towards the image,
as well as a cemented negative lens L22, which is of a negative
lens having a bi-concave shape and a positive lens of a meniscus
shape and whose convex surface is turned towards the object. The
third lens group G3 includes, in order and from the side of the
object, a cemented positive lens L3, which is of a positive lens of
a bi-convex shape and that has an aspherical surface on the object
side and a negative lens of a meniscus shape and whose concave
surface is tumed towards the object. The fourth lens group G4
includes, in order and from the side of the object, a cemented lens
L4, which is of a positive lens having a meniscus shape with an
aspherical surface on the object side and whose concave surface is
tumed towards the object and a negative lens of a men iscus shape
whose concave surface is tumed towards the object. The fifth lens
group G5 includes, in order and from the side of the object, a
negative lens L51 of a meniscus shape whose concave surface is
tumed towards the image, and a cemented lens L52, which is of a
positive lens of a bi-convex shape with an aspherical surface on
the object side and a negative lens of a meniscus shape whose
concave surface is turned towards the object. In addition, an
aperture stop S is positioned between the second lens group G2 and
the third lens group G3, and this aperture stop S moves in a
direction x of the optical axis as the lens position state
changes.
[0134] In table 1, the lens data of numerical embodiment 1, in
which actual numerical values are applied to the above-mentioned
first embodiment 1, are shown. In the tables indicating the lens
data of this numerical embodiment 1 as well as of each of the
numerical embodiments described afterwards, the surface number
indicates the ith optical surface counting from the side of the
object, the radius of curvature indicates the radius of curvature
of the ith surface counting from the side of the object, the
surface gap indicates the axial surface gap between the ith optical
surface counting from the side of the object and the i+/th optical
surface, the refractive index indicates the refractive index, with
respect to the d-line (.lamda.=587.6 nm), of the glass material
that has the ith optical surface on the object side, and the Abbe
number indicates the Abbe number, with respect to the d-line, of
the glass material that has the ith optical surface on the object
side. In addition, f indicates the focal length, FNO indicates the
F-number, and 2.omega. indicates the angle of field.
TABLE-US-00001 TABLE 1 f 1.00~2.05~4.24~7.39~14.10 FNO
2.86~3.26~3.64~3.70~4.61 2.omega.
71.67.degree.~36.11.degree.~18.01.degree.~10.38.degree.~5.42.degr-
ee. SURFACE RADIUS OF SURFACE REFRACTIVE ABHE NUMBER CURVATURE GAP
INDEX NUMBER 1: 10.9095 0.276 1.90366 31.1 2: 5.8998 1.168 1.49700
81.6 3: -32.2964 0.038 4: 5.0254 0.706 1.60300 65.5 5: 20.8025 (D5)
6: 12.0074 0.133 1.90366 31.1 7: 1.4993 1.027 8: -2.6542 0.114
1.48749 70.4 9: 2.4572 0.358 1.94595 18.0 10: 8.0874 (D10) 11:
0.0000 (D11) (Aperture Stop) 12: 4.2067 0.552 1.69350 53.3 13:
-2.5440 0.114 1.76182 26.6 14: -5.8499 (D14) 15: -5.5627 0.272
1.60300 65.5 16: -2.0160 0.076 1.90366 31.1 17: -2.7080 (D17) 18:
23.7981 0.095 1.88300 40.8 19: 2.8530 0.285 20: 2.3420 0.666
1.58313 59.5 21: -2.3784 0.095 1.84666 23.8 22: -4.0106 1.794 23:
0.0000 0.152 1.51680 64.2 24: 0.0000 (Bf)
[0135] The seventh, twelfth, fifteenth and twentieth surfaces are
aspherical. As 5 such, the fourth- (A), sixth- (B), eighth- (C) and
tenth-order (D) aspheric coefficients of these surfaces in
numerical embodiment 1 are shown in table 2 along with their conic
constants (K). It is noted that in table 2 and the subsequent
tables showing the aspherical coefficients, "E-i" is an exponential
notation to base 10, in other words, "E-i" represents "10.sup.-i",
and, "0.12345E-05" represents, for example,
"0.12345.times.10.sup.-5".
TABLE-US-00002 TABLE 2 7th .kappa. = 0.000000 A = -0.135737E-02 B =
-0.521916E-03 C = -0.347911E-02 D = +0.413344E-02 Surface 12.sup.th
.kappa. = 0.000000 A = -0.673780E-02 B = +0.479402E-02 C =
+0.796889E-02 D = +0.458605E-02 Surface 15.sup.th .kappa. =
0.000000 A = -0.627487E-02 B = -0.353678E-02 C = +0.663879E-02 D =
-0.423531E-02 Surface 20th .kappa. = 0.000000 A = -0.117751E-01 B =
+0.335768E-02 C = -0.409342E-02 D = +0.140861E-02 Surface
[0136] As the lens position state changes from the wide-angle end
state to the telephoto end state, surface gap D5 between the first
lens group G 1 and the second lens group G2, surface gap D10
between the second lens group G2 and the aperture stop S, surface
gap D11 between the aperture stop S and the third lens group G3,
surface gap D14 between the third lens group G3 and the fourth lens
group G4, and surface gap D17 between the fourth lens group G4 and
the fifth lens group G5 change. As such, values for each of the
above-mentioned surface gaps with respect to numerical embodiment 1
at the wide-angle end (f=1.000), three mid-focal lengths between
the wide-angle end and the telephoto end (f=2.053), (f=4.238) and
(f=7.393), and the telephoto end (f=14.105) are shown in table 3
along with the respective focal lengths f.
TABLE-US-00003 TABLE 3 (Variable Gap Table) f 1.000 2.053 4.238
7.393 14.105 Db 0.171 1.715 3.246 4.335 4.962 D10 4.414 2.381 1.252
0.754 0.514 D11 1.548 1.262 1.101 1.018 0.228 D14 1.956 1.423 0.854
1.030 2.635 D17 0.359 1.638 2.759 2.764 2.507 Bf 0.177 0.177 0.177
0.177 0.177
[0137] Corresponding values for conditional equations (1) through
(8) with respect to numerical embodiment 1 are indicated in table
4.
TABLE-US-00004 TABLE 4 f2a = -1.907 f2b = -8.853 f35w = 0.272 (1)
f2a/f2b = 0.215 (2) D12t/ft = 0.352 (3) n2P - n2N = 0.458 (4)
.beta.2w = -0.248 (5) .beta.2t = -1.539 (6) .DELTA.3/ft = 0.200 (7)
fw/f35w = 0.272 (8) Dsw/TLw = 0.492
[0138] FIGS. 3 through 7 show various aberration graphs for
numerical embodiment I focused at infinity, where FIG. 3 is for the
wide-angle end state (f=1.000), FIG. 4 is for a first mid-focal
length state (f=2.053), FIG. 5 is for a second mid-focal length
state (f=4.238), FIG. 6 is for a third mid-focal length state
(f=7.393), and FIG. 7 is for the telephoto end state
(f=14.105).
[0139] In the various aberration graphs in FIGS. 3 through 7, the
solid line in the spherical aberration graphs indicates spherical
aberration, the solid line in the astigmatism graphs indicates the
sagittal image plane while the broken line indicates the meridional
image plane. In the transverse aberration graphs, A represents the
angle of field, while y indicates the image height.
[0140] From these aberration graphs, it is obvious that various
aberrations are well corrected for in numerical embodiment 1, and
that numerical embodiment 1 is superior in terms of imaging
performance.
[0141] FIG. 8 illustrates the lens configuration of a second
embodiment 2 of a variable focal length lens system of the present
invention. A first lens group G1 includes, in order and from the
side of the object, a cemented lens L11, which is of a negative
lens having a meniscus shape and whose convex surface is turned
towards the object and a positive lens whose convex surface is
turned towards the object, as well as a positive lens L12 whose
convex surface is turned towards the object. A second lens group G2
includes, in order and from the side of the object, a negative lens
L21 of a meniscus shape that has an aspherical surface on the image
side and whose concave surface is turned towards the image, as well
as a cemented negative lens L22, which is of a negative lens having
a bi-concave shape and a positive lens of a meniscus shape and
whose convex surface is turned towards the object. A third lens
group G3 includes, in order and from the side of the object, a
cemented positive lens L3, which is of a positive lens of a
bi-convex shape and that has an aspherical surface on the object
side and a negative lens of a meniscus shape and whose concave
surface is turned towards the object. A fourth lens group G4
includes, in order and from the side of the object, a cemented lens
L4, which is of a positive lens having a meniscus shape with an
aspherical surface on the object side and whose concave surface is
turned towards the object and a negative lens of a meniscus shape
whose concave surface is turned towards the object. A fifth lens
group G5 includes, in order and from the side of the object, a
negative lens L51 of a meniscus shape whose concave surface is
turned towards the image, and a cemented lens L52, which is of a
positive lens of a bi-convex shape with an aspherical surface on
the object side and a negative lens of a meniscus shape whose
concave surface is turned towards the object. In addition, an
aperture stop S is positioned between the second lens group G2 and
the third lens group G3, and this aperture stop S moves in a
direction x of the optical axis as the lens position state
changes.
[0142] In table 5, the lens data of numerical embodiment 2, in
which actual numerical values are applied to the above-mentioned
second embodiment 2, are shown.
TABLE-US-00005 TABLE 5 f 1.00~2.05~4.24~7.39~14.10 FNO
2.86~3.26~3.64~3.70~4.61 2.omega.
71.67.degree.~36.11.degree.~18.01.degree.~10.38.degree.~5.42.degr-
ee. SURFACE RADIUS OF SURFACE REFRACTIVE ABHE NUMBER CURVATURE GAP
INDEX NUMBER 1: 10.5457 0.276 1.90366 31.1 2: 5.5755 1.065 1.49700
81.6 3: -48.9373 0.038 4: 4.8926 0.750 1.60300 65.5 5: 20.8886 (D5)
6: 11.1408 0.133 1.88300 40.8 7: 1.4287 0.951 8: -3.2164 0.114
1.48749 70.4 9: 2.0242 0.420 1.84666 23.8 10: 7.4083 (D10) 11:
0.0000 (D11) (Aperture Stop) 12: 4.1790 0.552 1.69350 53.3 13:
-2.6765 0.114 1.75520 27.5 14: -6.1128 (D14) 15: -5.4223 0.270
1.58313 59.5 16: -1.8453 0.076 1.90366 31.1 17: -2.4960 (D17) 18:
23.8024 0.095 1.88300 40.8 19: 2.8536 0.285 20: 2.3608 0.666
1.58313 59.5 21: -2.4097 0.095 1.84666 23.8 22: -4.0484 1.776 23:
0.0000 0.152 1.51680 64.2 24: 0.0000 (Bf)
[0143] The seventh, twelfth, fifteenth and twentieth surfaces are
all aspherical. As such, the fourth- (A), sixth- (B), eighth- (C)
and tenth-order (D) aspheric coefficients of these surfaces in
numerical embodiment 2 are shown in table 6 along with their conic
constants (.kappa.).
TABLE-US-00006 TABLE 6 7th .kappa. = 0.000000 A = -0.195289E-02 B =
-0.996592E-03 C = -0.452079E-02 D = +0.348160E-02 Surface 12.sup.th
.kappa. = 0.000000 A = -0.691555E-02 B = +0.394528E-02 C =
-0.598708E-02 D = +0.329867E-02 Surface 15.sup.th .kappa. =
0.000000 A = -0.679746E-02 B = -0.111337E-02 C = +0.190339E-02 D =
-0.118063E-02 Surface 20th .kappa. = 0.000000 A = -0.111597E-01 B =
+0.318369E-02 C = -0.371284E-02 D = +0.116364E-02 Surface
[0144] As the lens position state changes from the wide-angle end
state to the telephoto end state, surface gap D5 between the first
lens group G1 and the second lens group G2, surface gap D10 between
the second lens group G2 and the aperture stop 5, surface gap D11
between the aperture stop S and the third lens group G3, surface
gap D14 between the third lens group G3 and the fourth lens group
G4, and surface gap D17 between the fourth lens group G4 and the
fifth lens group G5 change. As such, values for each of the
above-mentioned surface gaps with respect to numerical embodiment 2
at the wide-angle end (f=1.000), three mid-focal lengths between
the wide-angle end and the telephoto end (f=1.977), (f32 3.860) and
(f=7.395), and the telephoto end (f=14.105) are shown in table 7
along with the respective focal lengths f.
TABLE-US-00007 TABLE 7 (Variable Gap Table) f 1.000 1.977 3.860
7.395 14.105 D5 0.171 1.701 3.114 4.452 5.121 D10 4.539 2.518 1.340
0.693 0.571 D11 1.605 1.319 1.158 1.075 0.285 D14 1.778 1.223 0.697
0.776 3.296 D17 0.449 1.611 2.661 2.733 1.740 Bf 0.177 0.177 0.177
0.177 0.177
[0145] Corresponding values for conditional equations (1) through
(8) with respect to numerical embodiment 2 are indicated in table
8.
TABLE-US-00008 TABLE 8 f2a = -1.868 f2b = -11.501 f35w = 0.277 (1)
f2a/f2b = 0.162 (2) D12t/ft = 0.363 (3) n2P - n2N = 0.359 (4)
.beta.2w = -0.252 (5) .beta.2t = -1.651 (6) .DELTA.3/ft = 0.199 (7)
fw/f35w = 0.277 (8) Dsw/TLw = 0.489
[0146] FIGS. 9 through 13 show various aberration graphs for
numerical embodiment 2 focused at infinity, where FIG. 9 is for the
wide-angle end state (f=1.000), FIG. 10 is for a first mid-focal
length state (f=1.977), FIG. 11 is for a second mid-focal length
state (f=3.860), FIG. 12 is for a third mid-focal length state
(f=7.395), and FIG. 13 is for the telephoto end state
(f=14.105).
[0147] In the various aberration graphs in FIGS. 9 through 13, the
solid line in the spherical aberration graphs indicates spherical
aberration, the solid line in the astigmatism graphs indicates the
sagittal image plane while the broken line indicates the meridional
image plane. In the transverse aberration graphs, A represents the
angle of field, while y indicates the image height.
[0148] From these aberration graphs, it is obvious that various
aberrations are well corrected for in numerical embodiment 2, and
that numerical embodiment 2 is superior in terms of imaging
performance.
[0149] FIG. 14 illustrates the lens configuration of a third
embodiment 3 of a variable focal length lens system of the present
invention. A first lens group G1 includes, in order and from the
side of the object, a cemented lens L11, which is of a negative
lens having a meniscus shape and whose convex surface is turned
towards the object and a positive lens whose convex surface is
turned towards the object, as well as a positive lens L12 whose
convex surface is tumed towards the object. A second lens group G2
includes, in order and from the side of the object, a negative lens
L21 of a meniscus shape that has an aspherical surface on the image
side and whose concave surface is turned towards the image, as well
as a cemented negative lens L22, which is of a negative lens having
a bi-concave shape and a positive lens of a meniscus shape and
whose convex surface is turned towards the object. A third lens
group G3 includes, in order and from the side of the object, a
cemented positive lens L3, which is of a. positive lens of a
bi-convex shape and that has an aspherical surface on the object
side and a negative lens of a meniscus shape and whose concave
surface is turned towards the object. A fourth lens group G4
includes, in order and fromthe side of the object, a cemented lens
L4, which is of a positive lens having a meniscus shape with an
aspherical surface on the object side and whose concave surface is
turned towards the object and a negative lens of a men iscus shape
whose concave surface is turned towards the object. A fifth lens
group G5 includes, in order and from the side of the object, a
negative lens L51 of a meniscus shape whose concave surface is
turned towards the image, and a cemented lens L52, which is of a
positive lens of a bi-convex shape with an aspherical surface on
the object side and a negative lens of a meniscus shape whose
concave surface is turned towards the object. It is noted that
there is an extremely thin resin layer on the image-side lens
surface of the negative lens L21 in the second lens group G2, and
that the image-side surface of this resin layer is aspherical. In
addition, an aperture stop S is positioned between the second lens
group G2 and the third lens group G3, and this aperture stop S
moves in a direction x of the optical axis as the lens position
state changes.
[0150] In table 9, the lens data of numerical embodiment 3, in
which actual numerical values are applied to the above-mentioned
third embodiment 3, are shown.
TABLE-US-00009 TABLE 9 f 1.00~2.05~4.24~7.39~14.10 FNO
2.86~3.26~3.64~3.70~4.61 2.omega.
71.67.degree.~36.11.degree.~18.01.degree.~10.38.degree.~5.42.degr-
ee. SURFACE RADIUS OF SURFACE REFRACTIVE ABHE NUMBER CURVATURE GAP
INDEX NUMBER 1: 11.6243 0.276 1.90366 31.1 2: 5.9054 1.079 1.49700
81.6 3: -33.4114 0.038 4: 5.0031 0.729 1.60300 65.5 5: 20.9308 (D5)
6: 10.8446 0.133 1.88300 40.8 7: 1.4643 0.019 1.53420 41.7 8:
1.4648 0.921 9: -3.1331 0.114 1.48749 70.4 10: 2.0122 0.420 1.84666
23.8 11: 0.0000 (D11) 12: 0.0000 (D12) (Aperture Stop) 13: 4.0413
0.552 1.69350 53.3 14: -2.7308 0.114 1.75520 27.5 15: -6.2793 (D15)
16: -4.6751 0.257 1.58313 59.5 17: -1.8286 0.076 1.90366 31.1 18:
-2.4194 (D18) 19: 23.8018 0.095 1.88300 40.8 20: 2.8535 0.293 21:
2.3568 0.666 1.58313 59.5 22: -2.3938 0.095 1.84666 23.8 23:
-4.0070 1.866 24: 0.0000 0.095 1.51680 64.2 25: 0.0000 (Bf)
[0151] The eighth, thirteenth, sixteenth and twenty-first surfaces
are all aspherical. As such, the fourth- (A), sixth- (B), eighth-
(C) and tenth-order (D) aspheric coefficients of these surfaces in
numerical embodiment 3 are shown in table 10 along with their conic
constants (.kappa.).
TABLE-US-00010 TABLE 10 8th .kappa. = 0.000000 A = -0.434984E-03 B
= +0.572353E-02 C = -0.126050E-01 D = +0.978155E-02 Surface 13th
.kappa. = 0.000000 A = -0.689014E-02 B = +0.425011E-02 C =
-0.697951E-02 D = +0.398211E-02 Surface 16th .kappa. = 0.000000 A =
-0.755406E-02 B = -0.208868E-02 C = +0.370596E-02 D = -0.231137E-02
Surface 21st .kappa. = 0.000000 A = -0.115363E-01 B = +0.325661E-02
C = -0.395446E-02 D = +0.128002E-02 Surface
[0152] As the lens position state changes from the wide-angle end
state to the telephoto end state, surface gap D5 between the first
lens group G1 and the second lens group G2, surface gap D11 between
the second lens group G2 and the aperture stop S, surface gap D12
between the aperture stop S and the third lens group G3, surface
gap D15 between the third lens group G3 and the fourth lens group
G4, and surface gap D18 between the fourth lens group G4 and the
fifth lens group G5 change. As such, values for each of the
above-mentioned surface gaps with respect to numerical embodiment 3
at the wide-angle end (f=1.000), three mid-focal lengths between
the wide-angle end and the telephoto end (f=1.977), (f=3.860) and
(f=7.394), and the telephoto end (f=14.105) are shown in table 11
along with the respective focal lengths f.
TABLE-US-00011 TABLE 11 (Variable Gap Table) f 1.000 1.977 3.860
7.394 14.105 D5 0.171 1.761 3.185 4.556 5.222 D11 4.581 2.594 1.399
0.762 0.571 D12 1.605 1.319 1.158 1.075 0.285 D15 1.804 1.240 0.677
0.804 3.098 D18 0.316 1.502 2.612 2.646 1.771 Bf 0.214 0.214 0.214
0.214 0.214
[0153] Corresponding values for conditional equations (1) through
(8) with respect to numerical embodiment 3 are indicated in table
12.
TABLE-US-00012 TABLE 12 f2a = -1.928 f2b = -10.606 f35w = 0.278 (1)
f2a/f2b = 0.182 (2) D12t/ft = 0.370 (3) n2P - n2N = 0.359 (4)
.beta.2w = -0.250 (5) .beta.2t = -1.619 (6) .DELTA.3/ft = 0.195 (7)
fw/f35w = 0.278 (8) Dsw/TLw = 0.487
[0154] FIGS. 15 through 19 show various aberration graphs for
numerical. embodiment 3 focused at infinity, where FIG. 15 is for
the wide-angle end state (f=1.000), FIG. 16 is for a first
mid-focal length state (f=1.977), FIG. 17 is for a second mid-focal
length state (f=3.860), FIG. 18 is for a third mid-focal length
state (f=7.394), and FIG. 19 is for the telephoto end state
(f=14.105).
[0155] In the various aberration graphs in FIGS. 15 through 19, the
solid line in the spherical aberration graphs indicates spherical
aberration, the solid line in the astigmatism graphs indicates the
sagittal image plane while the broken line indicates the meridional
image plane. In the transverse aberration graphs, A represents the
angle of field, while y indicates the image height.
[0156] From these aberration graphs, it is obvious that various
aberrations are well corrected for in numerical embodiment 3, and
that numerical embodiment 3 is superior in terms of imaging
performance.
[0157] FIG. 20 illustrates the lens configuration of a fourth
embodiment 4 of a variable focal length lens system of the present
invention. A first lens group G1 includes, in order and from the
side of the object, a cemented lens L11, which is of a negative
lens having a meniscus shape and whose convex surface is turned
towards the object and a positive lens whose convex surface is
turned towards the object, as well as a positive lens L12 whose
convex surface is turned towards the object. A second lens group G2
includes, in order and from the side of the object, a negative lens
L21 of a meniscus shape that has an aspherical surface on the image
side and whose concave surface is turned towards the image, as well
as a cemented negative lens L22, which is of a negative lens having
a bi-concave shape and a positive lens of a meniscus shape and
whose convex surface is turned towards the object. A third lens
group G3 includes, in order and from the side of the object, a
cemented positive lens L3, which is of a positive lens of a
bi-convex shape and that has an aspherical surface on the object
side and a negative lens of a meniscus shape and whose concave
surface is turned towards the object. A fourth lens group G4
includes, in order and from the side of the object, a cemented lens
L4, which is of a positive lens having a meniscus shape with an
aspherical surface on the object side and whose concave surface is
turned towards the object and a negative lens of a meniscus shape
whose concave surface is turned towards the object. A fifth lens
group G5 includes, in order and from the side of the object, a
negative lens L51 of a meniscus shape whose concave surface is
turned towards the image, and a cemented lens L52, which is of a
positive lens of a bi-convex shape with an aspherical surface on
the object side and a negative lens of a meniscus shape whose
concave surface is turned towards the object. It is noted that
there is an extremely thin resin layer on the image-side lens
surface of the negative lens L21 in the second lens group G2, and
that the image-side surface of this resin layer is aspherical. In
addition, an aperture stop S is positioned in proximity to the
third lens group G3 on its object side, and this aperture stop S
moves in a direction x of the optical axis together with the third
lens group G3 as the lens position state changes.
[0158] In table 13, the lens data of numerical embodiment 4, in
which actual numerical values are applied to the above-mentioned
fourth embodiment 4, are shown.
TABLE-US-00013 TABLE 13 f 1.00~2.05~4.24~7.39~14.10 FNO
2.86~3.26~3.64~3.70~4.61 2.omega.
71.67.degree.~36.11.degree.~18.01.degree.~10.38.degree.~5.42.degr-
ee. SURFACE RADIUS OF SURFACE REFRACTIVE ABHE NUMBER CURVATURE GAP
INDEX NUMBER 1: 11.6243 0.276 1.90366 31.1 2: 5.9054 1.079 1.49700
81.6 3: -33.4114 0.038 4: 5.0031 0.729 1.60300 65.5 5: 20.9308 (D5)
6: 10.8446 0.133 1.88300 40.8 7: 1.4643 0.019 1.53420 41.7 8:
1.4648 0.921 9: -3.1331 0.114 1.48749 70.4 10: 2.0122 0.420 1.84666
23.8 11: 7.1401 (D11) 12: 0.0000 0.285 (Aperture Stop) 13: 4.0413
0.552 1.69350 53.3 14: -2.7308 0.114 1.75520 27.5 15: -6.2793 (D15)
16: -4.6751 0.257 1.58313 59.5 17: -1.8286 0.076 1.90366 31.1 18:
-2.4194 (D18) 19: 23.8018 0.095 1.88300 40.8 20: 2.8535 0.293 21:
2.3568 0.666 1.58313 59.5 22: -2.3938 0.095 1.84666 23.8 23:
-4.0070 1.866 24: 0.0000 0.095 1.51680 64.2 25: 0.0000 (Bf)
[0159] The eighth, thirteenth, sixteenth and twenty-first surfaces
are all aspherical. As such, the fourth- (A), sixth- (B), eighth-
(C) and tenth-order (D) aspheric coefficients of these surfaces in
numerical embodiment 4 are shown in table 14 along with their conic
constants (.kappa.).
TABLE-US-00014 TABLE 14 8th .kappa. = 0.000000 A = -0.434984E-03 B
= +0.572353E-02 C = -0.126050E-01 D = +0.978155E-02 Surface 13th
.kappa. = 0.000000 A = -0.689014E-02 B = +0.425011E-02 C =
-0.697951E-02 D = +0.398211E-02 Surface 16th .kappa. = 0.000000 A =
-0.755406E-02 B = -0.208868E-02 C = +0.370596E-02 D = -0.231137E-02
Surface 21st .kappa. = 0.000000 A = -0.115363E-01 B = +0.325661E-02
C = -0.395446E-02 D = +0.128002E-02 Surface
[0160] As the lens position state changes from the wide-angle end
state to the telephoto end state, surface gap D5 between the first
lens group G1 and the second lens group G2, surface gap D11 between
the second lens group G2 and the aperture stop S, surface gap D15
between the third lens group G3 and the fourth lens group G4, and
surface gap D18 between the fourth lens group 04 and the fifth lens
group G5 change. As such, values for each of the above-mentioned
surface gaps with respect to numerical embodiment 4 at the
wide-angle end (f=1.000), three mid-focal lengths between the
wide-angle end and the telephoto end (f=1.977), (f=3.860) and
(f=7.394), and the telephoto end (f=14.105) are shown in table 15
along with the respective focal lengths f.
TABLE-US-00015 TABLE 15 (Variable Gap Table) f 1.000 1.977 3.860
7.394 14.105 D5 0.171 1.761 3.185 4.556 5.222 D11 4.581 2.594 1.399
0.762 0.511 D15 1.804 1.240 0.677 0.804 3.098 D18 0.316 1.502 2.612
2.646 1.771 Bf 0.214 0.214 0.214 0.214 0.214
[0161] Corresponding values for conditional equations (1) through
(8) with respect to numerical embodiment 4 are indicated in table
16.
TABLE-US-00016 TABLE 16 f2a = -1.928 f2b = -10.606 f35w = 0.278 (1)
f2a/f2b = 0.182 (2) D12t/ft = 0.370 (3) n2P - n2N = 0.359 (4)
.beta.2w = -0.250 (5) .beta.2t = -1.619 (6) .DELTA.3/ft = 0.195 (7)
fw/f35w = 0.278 (8) Dsw/TLw = 0.407
[0162] FIGS. 21 through 25 show various aberration graphs for
numerical embodiment 4 focused at infinity, where FIG. 21 is for
the wide-angle end state (f=1.000), FIG. 22 is for a first
mid-focal length state (f=1.977), FIG. 23 is for a second mid-focal
length state (f=3.860), FIG. 24 is for a third mid-focal length
state (f=7.394), and FIG. 25 is for the telephoto end state
(f=14.105).
[0163] In the various aberration graphs in FIGS. 21 through 25, the
solid line in the spherical aberration graphs indicates spherical
aberration, the solid line in the astigmatism graphs indicates the
sagittal image plane while the broken line indicates the meridional
image plane. In the transverse aberration graphs, A represents the
angle of field, while y indicates the image height.
[0164] From these aberration graphs, it is obvious that various
aberrations are well corrected for in numerical embodiment 4, and
that numerical embodiment 4 is superior in terms of imaging
performance.
[0165] In the above-mentioned embodiments 1 to 4, if a
configuration is adopted where the fifth lens group G5 is fixed in
the direction of optical axis x but a partial parts group (for
example, the positive parts group L52) in the fifth lens group G5
can be shifted in a direction that is perpendicular to optical axis
x so as to shift the image, the transverse magnification of the
positive parts group L52 in the fifth lens group G5 can be varied
by moving the fifth lens group G5 in the direction of optical axis
x, and the shift amount that is required for a correction by a
predetermined angle can be brought closer between the telephoto end
state and the wide-angle end state.
[0166] In addition to the above-mentioned first to fourth
embodiments 1 to 4, a variable focal length lens system of the
present invention may also be configured with the allocation of
refractive power like the one shown in FIG. 26.
[0167] In other words, a variable focal length lens system 5
according to a fifth embodiment of the present invention includes,
in order and from the side of the object, a first lens group G1
having a positive refractive power, a second lens group G2 having a
negative refractive power, a third lens group G3 haying a positive
refractive power, and a fourth lens group G4 having a positive
refractive power. In zooming from a wide-angle end state (the state
shown on the upper side) to a telephoto end state (the state shown
on the lower side), the first lens group through the fourth lens
group move along an optical axis x in such a manner that the air
gap between the first lens group G1 and the second lens group G2
widens, while the air gap between the second lens group G2 and the
third lens group G3 narrows. Here, after first moving towards the
image, the first lens group G1 then moves towards the object, while
the second lens group G2 moves towards the image, the third lens
group G3 moves towards the object, and the fourth lens group G4
moves so as to correct for changes in the position of the image
plane that occur in association with the movements of each lens
group while it also moves towards the object during close-range
focusing.
[0168] Even with this fifth embodiment, it is still possible to
reap the benefits of the present invention.
[0169] It is noted that, with respect to embodiments 1 through 5,
it is naturally possible to provide a low pass filter in order to
prevent occurrences of moire stripes on the image side of the lens
system or to provide an infrared cut filter in accordance with the
spectral sensitivity characteristics of the photoelectric
transducers.
[0170] An imaging apparatus according to an embodiment of the
present invention includes a variable focal length lens system, and
an imaging device which converts an optical image formed by the
above-mentioned variable focal length lens system into electric
signals. The above-mentioned variable focal length lens system
includes, in order and from the side of the object, a first lens
group having a positive refractive power, a second lens group
having a negative refractive power, a third lens group having a
positive refractive power, and a fourth lens group having a
positive refractive power. When the lens position changes from a
wide-angle end state, where the focal length is shortest, to a
telephoto end state, where the focal length is greatest, at least
each of the lens groups from the above-mentioned first lens group
to the above-mentioned fourth lens group is mobile, and the
above-mentioned second lens group moves towards the image while the
above-mentioned third lens group moves towards the object so that
the gap between the above-mentioned first lens group and the
above-mentioned second lens group grows bigger, while the gap
between the above-mentioned second lens group and the
above-mentioned third lens group becomes smaller. At the same time,
the above-mentioned fourth lens group moves in the direction of the
optical axis in order to compensate for changes in the position of
the plane of the image that accompany the movement of each of the
lens groups. The above-mentioned first lens group is positioned
closer to the object in the telephoto end state as compared to the
wide-angle end state. The second lens group includes, in order and
from the side of the object, a negative lens of a meniscus shape
having a concave surface and an aspherical surface on the image
side, a cemented negative lens, which is of a biconcave lens and a
positive lens of a meniscus shape that has its convex surface
facing the object. In addition, the following conditional equations
hold true: (1) 0.15<f2a/f2b<0.3, and (2)
0.3<D12t/ft<0.45. Thus, with an imaging apparatus of the
present embodiment, while keeping itself small, it is possible to
achieve imaging with a high zoom ratio.
[0171] FIG. 27 is a block diagram illustrating a specific
embodiment of an imaging apparatus of the present invention.
[0172] An imaging apparatus 10 includes a variable focal length
lens system 20, and an imaging device 30 which converts an optical
image formed by the above-mentioned variable focal length lens
system 20 into electric signals. As examples of the imaging device
30, such photoelectric transducers as CCDs (Charge Coupled Devices)
and CMOSs (Complementary Metal-Oxide Semiconductors) and the like
may be used. For the above-mentioned variable focal length lens
system 20, a variable focal length lens system according to the
present embodiment may be used, and in FIG. 27, a variable focal
length lens system 1 according to the first embodiment shown in
FIG. 1 is illustrated in a simplified manner where each of the lens
groups is shown as a single lens. Naturally, in addition to the
variable focal length lens system 1 according to the first
embodiment, variable focal length lens systems 2 through 5
according to the second through fifth embodiments, or a variable
focal length lens system of the present invention configured in a
manner that is different from those disclosed in the present
specification may also be used.
[0173] Electric signals formed by the above-mentioned imaging
device 30 are sent to a control circuit 50 as focus control signals
by an image separation circuit 40, and image signals are sent to an
image processing circuit. Signals sent to the image processing
circuit are processed to a state that is suitable for subsequent
processing, and are provided to various processes such as
displaying by a display apparatus, recording to a recording medium,
transferring by communications means and the like.
[0174] External operation signals, such as operations through a
zoom button and the like, for example, are inputted to the control
circuit 50, and various processes are performed in accordance with
these operation signals. For example, if a zoom command by way of
the zoom button is inputted, in order to realize the focal length
state that is commanded, drive sections 51a, 52a, 53a and 54a are
made to operate via driver circuits 51, 52, 53 and 54, thereby
moving the first lens group G1, the second lens group G2, the third
lens group G3 and the fourth lens group G4 to predetermined
positions. Positional information regarding the first lens group
G1, the second lens group G2, the third lens group G3 and the
fourth lens group G4 obtained through respective sensors 51b, 52b,
53b and 54b is inputted to the control circuit 50 and are referred
to in outputting command signals to the driver circuits 51, 52, 53
and 54. In addition, the control circuit 50 checks the focus state
based on signals sent from the above-mentioned image separation
circuit 40, and controls, for example, the fourth lens group G4 via
the driver circuit 54 in order to obtain the optimal focus
state.
[0175] The above-mentioned imaging apparatus 10 may be applied to
various products. For example, it may be applied widely to various
cameras, such as digital still cameras, digital video cameras and
the like, or as the camera section of digital devices such as
mobile phones into which cameras are incorporated or PDAs (Personal
Digital Assistants) into which cameras are incorporated.
[0176] It is noted that the application of a zoom lens of the
present invention is by no means limited to digital cameras, and
that it may of course be applied to, for example, cameras that use
silver salt films as media.
[0177] In addition, the specific forms and structures of the
various parts and the numerical values indicated in the embodiments
and numerical embodiments described herein are merely examples for
implementing the present invention, and the scope of the invention
should in no way be limited thereby.
* * * * *