VARIABLE MAGNIFICATION OPTICAL SYSTEM, OPTICAL APPARATUS, AND METHOD FOR MANUFACTURING VARIABLE MAGNIFICATION OPTICAL SYSTEM

FIELD

The present invention relates to a variable magnification optical system, an optical apparatus, and a method for manufacturing a variable magnification optical system.

BACKGROUND

Variable magnification optical systems used for cameras for photographs, electronic still cameras, video cameras and the like have been proposed (see, e.g., Patent Literature 1).

CITATION LIST
Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No. 2004-198529

SUMMARY

A variable magnification optical system of the present disclosure includes a plurality of lens groups; upon varying magnification the distances between the lens groups are varied; a final lens group closest to an image side of the lens groups includes at least one lens surface having a pole; and the following conditional equation is satisfied. A pole in the present disclosure refers to a point on a lens surface other than on an optical axis at which the optical axis crosses the tangent plane of the lens surface perpendicularly.

0.50<TL/fw<10.00

where

TL denotes the shorter of the total optical length in a wide-angle end state and the total optical length in a telephoto end state of the variable magnification optical system, and

fw denotes the focal length of the variable magnification optical system in the wide-angle end state.

−5.00<fRI/fR<5.00

where

fRI denotes the focal length of a lens in the final lens group including a lens surface having a pole, and

fR denotes the focal length of the final lens group.

A method for manufacturing a variable magnification optical system of the present disclosure is a method for manufacturing a variable magnification optical system including a plurality of lens groups. The method includes arranging the lens groups so that upon varying magnification the distances between the lens groups are varied; arranging so that a final lens group closest to an image side of the lens groups includes at least one lens surface having a pole; and arranging so that the following conditional equation is satisfied:

0.50<TL/fw<10.00

where

TL denotes the shorter of the total optical length in a wide-angle end state and the total optical length in a telephoto end state of the variable magnification optical system, and

fw denotes the focal length of the variable magnification optical system in the wide-angle end state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a variable magnification optical system of a first example.

FIG. 2A illustrates aberrations of the variable magnification optical system of the first example in the wide-angle end state.

FIG. 2B illustrates aberrations of the variable magnification optical system of the first example in an intermediate focal length state.

FIG. 2C illustrates aberrations of the variable magnification optical system of the first example in the telephoto end state.

FIG. 3 is a cross-sectional view of a variable magnification optical system of a second example.

FIG. 4A illustrates aberrations of the variable magnification optical system of the second example in the wide-angle end state.

FIG. 4B illustrates aberrations of the variable magnification optical system of the second example in an intermediate focal length state.

FIG. 4C illustrates aberrations of the variable magnification optical system of the second example in the telephoto end state.

FIG. 5 is a cross-sectional view of a variable magnification optical system of a third example.

FIG. 6A illustrates aberrations of the variable magnification optical system of the third example in the wide-angle end state.

FIG. 6B illustrates aberrations of the variable magnification optical system of the third example in an intermediate focal length state.

FIG. 6C illustrates aberrations of the variable magnification optical system of the third example in the telephoto end state.

FIG. 7 is a cross-sectional view of a variable magnification optical system of a fourth example.

FIG. 8A illustrates aberrations of the variable magnification optical system of the fourth example in the wide-angle end state.

FIG. 8B illustrates aberrations of the variable magnification optical system of the fourth example in an intermediate focal length state.

FIG. 8C illustrates aberrations of the variable magnification optical system of the fourth example in the telephoto end state.

FIG. 9 is a cross-sectional view of a variable magnification optical system of a fifth example.

FIG. 10A illustrates aberrations of the variable magnification optical system of the fifth example in the wide-angle end state.

FIG. 10B illustrates aberrations of the variable magnification optical system of the fifth example in an intermediate focal length state.

FIG. 10C illustrates aberrations of the variable magnification optical system of the fifth example in the telephoto end state.

FIG. 11 schematically illustrates a camera including a variable magnification optical system of the embodiment.

FIG. 12 is a schematic flowchart of a method for manufacturing a variable magnification optical system of the embodiment.

DESCRIPTION OF EMBODIMENTS

The following describes a variable magnification optical system, an optical apparatus, and a method for manufacturing a variable magnification optical system of an embodiment of the present application.

A variable magnification optical system of the present embodiment includes a plurality of lens groups; upon varying magnification the distances between the lens groups are varied; and a final lens group closest to an image side of the lens groups includes at least one lens surface having a pole.

Such a configuration enables the variable magnification optical system of the present embodiment to correct aberrations favorably and achieving downsizing of the variable magnification optical system.

Additionally, the variable magnification optical system of the present embodiment satisfies the following conditional equation:

0.50<TL/fw<10.00 (1)

where

TL denotes the shorter of the total optical length in a wide-angle end state and the total optical length in a telephoto end state of the variable magnification optical system, and

fw denotes the focal length of the variable magnification optical system in the wide-angle end state.

The variable magnification optical system of the present embodiment can correct curvature of field favorably by making the ratio of the total optical length of the variable magnification optical system to the focal length of the variable magnification optical system in the wide-angle end state in conditional equation (1) greater than the lower limit. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (1) at 0.50. To further ensure the effect of the present embodiment, the lower limit of conditional equation (1) is preferably set at 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 2.75, or 3.00, more preferably at 3.10.

The variable magnification optical system of the present embodiment can correct aberrations favorably and be downsized by making the ratio of the total optical length of the variable magnification optical system to the focal length of the variable magnification optical system in the wide-angle end state in conditional equation (1) less than the upper limit. The effect of the present embodiment can be further ensured by setting the upper limit of conditional equation (1) at 10.00. To further ensure the effect of the present embodiment, the upper limit of conditional equation (1) is preferably set at 9.50, 9.00, 8.50, 8.00, 7.75, 7.50, 7.25, 7.00, 6.80, or 6.60, more preferably at 6.50.

A small-sized variable magnification optical system of favorable optical performance can be achieved by the above configuration.

Additionally, the variable magnification optical system of the present embodiment satisfies the following conditional equation:

−5.00<fRI/fR<5.00 (2)

where

fRI denotes the focal length of a lens in the final lens group including a lens surface having a pole, and

fR denotes the focal length of the final lens group.

Conditional equation (2) defines the ratio of the focal length of a lens in the final lens group including a lens surface having a pole to the focal length of the final lens group. The variable magnification optical system of the present embodiment satisfying conditional equation (2) can correct curvature of field favorably.

To further ensure the effect of the present embodiment, the lower limit of conditional equation (2) is preferably set at −4.50, −4.00, −3.75, −3.50, −3.25, −3.00, −2.75, −2.50, −2.00, −1.60, −1.30, −1.00, −0.50, −0.10, 0.10, or 0.30, more preferably at 0.50. To further ensure the effect of the present embodiment, the upper limit of conditional equation (2) is preferably set at 4.50, 4.00, 3.50, 3.00, 2.75, 2.50, 2.25, 2.00, 1.75, 1.50, 1.35, 1.20, or 1.15, more preferably at 1.10.

A small-sized variable magnification optical system of favorable optical performance can be achieved by the above configuration.

In the variable magnification optical system of the present embodiment, the lens groups preferably include at least one focusing lens group having positive refractive power and configured to move in the direction of an optical axis at focusing.

The variable magnification optical system of the present embodiment having such a configuration can reduce variations in curvature of field at focusing.

In the variable magnification optical system of the present embodiment, one of the at least one focusing lens group is preferably adjacent to the final lens group.

The variable magnification optical system of the present embodiment having such a configuration can reduce variations in curvature of field at focusing.

The variable magnification optical system of the present embodiment preferably satisfies the following conditional equation:

0.20<|fF/fR|<5.00 (3)

where

fF denotes the focal length of the focusing lens group adjacent to the final lens group, and

fR denotes the focal length of the final lens group.

The variable magnification optical system of the present embodiment can reduce the power of the focusing lens group and variations in coma aberration at focusing by making the ratio of the focal length of the focusing lens group adjacent to the final lens group to the focal length of the final lens group in conditional equation (3) greater than the lower limit. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (3) at 0.20. To further ensure the effect of the present embodiment, the lower limit of conditional equation (3) is preferably set at 0.30, 0.40, 0.50, 0.60, 0.70, 0.75, 0.80, 0.85, 0.90, 0.93, 0.95, or 0.98, more preferably at 1.00.

The variable magnification optical system of the present embodiment can reduce the moving distance of the focusing lens group and variations in coma aberration at focusing by making the ratio of the focal length of the focusing lens group adjacent to the final lens group to the focal length of the final lens group in conditional equation (3) less than the upper limit. The effect of the present embodiment can be further ensured by setting the upper limit of conditional equation (3) at 5.00. To further ensure the effect of the present embodiment, the upper limit of conditional equation (3) is preferably set at 4.75, 4.50, 4.25, 4.00, 3.80, 3.60, or 3.50, more preferably at 3.40.

Preferably, the variable magnification optical system of the present embodiment further includes an aperture stop; the lens groups preferably include a front group including one or more lens groups closer to an object side than the aperture stop; a rear group placed closer to the image side than the aperture stop, including the focusing lens group, and having positive refractive power; and the final lens group placed closer to the image side than the rear group and having negative refractive power.

The variable magnification optical system of the present embodiment having such a configuration can reduce variations in aberrations at varying magnification.

Preferably, the variable magnification optical system of the present embodiment includes a plurality of lenses respectively including lens surfaces having a pole; of the lens surfaces having a pole, at least two lens surfaces are adjacent to each other with an air layer in between; and the radii of curvature of the two lens surfaces adjacent to each other with an air layer in between have the same sign on an optical axis.

The variable magnification optical system of the present embodiment having such a configuration can correct curvature of field favorably because of a difference in image height between adjacent lenses.

In the variable magnification optical system of the present embodiment, a final lens in the final lens group closest to the image side preferably includes a lens surface having a pole.

The variable magnification optical system of the present embodiment having such a configuration can correct curvature of field favorably because luminous flux is divided at the final lens according to image heights.

The variable magnification optical system of the present embodiment preferably satisfies the following conditional equation:

0.20<|fRI/fw|<5.00 (4)

where

fRI denotes the focal length of a lens in the final lens group including a lens surface having a pole.

The variable magnification optical system of the present embodiment satisfying conditional equation (4) can correct curvature of field and the like favorably. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (4) at 0.20. To further ensure the effect of the present embodiment, the lower limit of conditional equation (4) is preferably set at 0.30, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, or 0.80, more preferably at 0.85.

The effect of the present embodiment can be further ensured by setting the upper limit of conditional equation (4) at 5.00. To further ensure the effect of the present embodiment, the upper limit of conditional equation (4) is preferably set at 4.80, 4.50, 4.35, 4.00, 3.85, 3.70, 3.50, 3.35, 3.10, 3.00, or 2.85, more preferably at 2.70.

In the variable magnification optical system of the present embodiment, one of the at least one lens surface in the final lens group having a pole preferably satisfies the following conditional equation:

0.10<k/h<1.00 (5)

where

k denotes the height of the pole from an optical axis, and

h denotes the effective radius of the lens surface having a pole.

The variable magnification optical system of the present embodiment satisfying conditional equation (5) can correct curvature of field and astigmatism favorably. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (5) at 0.10. To further ensure the effect of the present embodiment, the lower limit of conditional equation (5) is preferably set at 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, or 0.70, more preferably at 0.72.

The effect of the present embodiment can be further ensured by setting the upper limit of conditional equation (5) at 1.00. To further ensure the effect of the present embodiment, the upper limit of conditional equation (5) is preferably set at 0.99, 0.97, 0.95, 0.94, 0.93, or 0.92, more preferably at 0.90.

In the variable magnification optical system of the present embodiment, a lens surface closest to the image side of the at least one lens surface in the final lens group having a pole preferably satisfies the following conditional equation:

0.40<k/h<1.00. (6)

The variable magnification optical system of the present embodiment satisfying conditional equation (6) can correct curvature of field and astigmatism favorably. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (6) at 0.40. To further ensure the effect of the present embodiment, the lower limit of conditional equation (6) is preferably set at 0.43, 0.45, 0.48, 0.50, 0.52, 0.54, 0.60, 0.65, 0.70, or 0.75, more preferably at 0.78.

The effect of the present embodiment can be further ensured by setting the upper limit of conditional equation (6) at 1.00. To further ensure the effect of the present embodiment, the upper limit of conditional equation (6) is preferably set at 0.99, 0.98, 0.97, 0.95, or 0.93, more preferably at 0.90.

The variable magnification optical system of the present embodiment preferably satisfies the following conditional equation:

0.10<BFw/fw<1.00 (7)

where

BFw denotes the back focus of the variable magnification optical system in the wide-angle end state.

The variable magnification optical system of the present embodiment facilitates disposing a mechanical member of a barrel by making the ratio of the back focus of the variable magnification optical system in the wide-angle end state to the focal length of the variable magnification optical system in the wide-angle end state in conditional equation (7) less than the lower limit. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (7) at 0.10. To further ensure the effect of the present embodiment, the lower limit of conditional equation (7) is preferably set at 0.15, 0.18, 0.20, or 0.23, more preferably at 0.25.

The variable magnification optical system of the present embodiment can prevent increase in field curvature aberration caused by symmetry breaking of the optical system, by making the ratio of the back focus of the variable magnification optical system in the wide-angle end state to the focal length of the variable magnification optical system in the wide-angle end state in conditional equation (7) less than the upper limit. The effect of the present embodiment can be further ensured by setting the upper limit of conditional equation (7) at 1.00. To further ensure the effect of the present embodiment, the upper limit of conditional equation (7) is preferably set at 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, or 0.55, more preferably at 0.50.

The variable magnification optical system of the present embodiment preferably satisfies the following conditional equation:

29.00<νR (8)

where

νR denotes the Abbe number of one of lenses in the final lens group including a lens surface having a pole.

The variable magnification optical system of the present embodiment can correct chromatic aberration favorably by making the value of conditional equation (8) greater than the lower limit. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (8) at 29.00. To further ensure the effect of the present embodiment, the lower limit of conditional equation (8) is preferably set at 30.00, 33.00, 35.00, or 38.00, more preferably at 40.00.

The variable magnification optical system of the present embodiment preferably satisfies the following conditional equation:

29.00<νR1 (9)

where

νR1 denotes the Abbe number of a lens closest to the image side of lenses in the final lens group including a lens surface having a pole.

The variable magnification optical system of the present embodiment can correct chromatic aberration favorably by making the value of conditional equation (9) greater than the lower limit. The effect of the present embodiment can be further ensured by setting the lower limit of conditional equation (9) at 29.00. To further ensure the effect of the present embodiment, the lower limit of conditional equation (9) is preferably set at 30.00, 33.00, 35.00, or 38.00, more preferably at 40.00.

A small-sized variable magnification optical system of favorable optical performance can be achieved by the above configuration.

An optical apparatus of the present embodiment includes a variable magnification optical system having the above configuration. This enables achieving a small-sized optical apparatus of favorable optical performance.

A method for manufacturing a variable magnification optical system of the present embodiment is a method for manufacturing a variable magnification optical system including a plurality of lens groups. The method includes arranging the lens groups so that upon varying magnification the distances between the lens groups are varied; arranging so that a final lens group closest to an image side of the lens groups includes at least one lens surface having a pole; and arranging so that the following conditional equation (1) is satisfied:

0.50<TL/fw<10.00 (1)

where

TL denotes the shorter of the total optical length in a wide-angle end state and the total optical length in a telephoto end state of the variable magnification optical system, and

fw denotes the focal length of the variable magnification optical system in the wide-angle end state.

A small-sized variable magnification optical system of favorable optical performance can be manufactured by such a method for manufacturing a variable magnification optical system.

NUMERICAL EXAMPLES

Examples of the present application will be described below with reference to the drawings.

First Example

FIG. 1 is a cross-sectional view of a variable magnification optical system of a first example.

The variable magnification optical system of the present example includes a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, a fifth lens group G5 having positive refractive power, a sixth lens group G6 having positive refractive power, and a seventh lens group G7 having negative refractive power, in order from an object side. The seventh lens group G7 is a final lens group closest to an image side of the lens groups. An aperture stop S is disposed between the third lens group G3 and the fourth lens group G4.

The first lens group G1 consists of a negative meniscus lens L11 convex on the object side and a positive cemented lens composed of a negative meniscus lens L12 convex on the object side and a positive meniscus lens L13 convex on the object side, in order from the object side.

The second lens group G2 consists of a positive cemented lens composed of a biconvex positive lens L21 and a negative meniscus lens L22 convex on the image side.

The third lens group G3 consists of a positive cemented lens composed of a negative meniscus lens L31 convex on the object side and a biconvex positive lens L32.

The fourth lens group G4 consists of a biconcave negative lens L41, a positive meniscus lens L42 convex on the object side, and a positive meniscus lens L43 convex on the object side.

The fifth lens group G5 consists of a positive cemented lens composed of a biconvex positive lens L51 and a negative meniscus lens L52 convex on the image side.

The sixth lens group G6 consists of a biconvex positive lens L61.

The seventh lens group G7 consists of a positive cemented lens composed of a positive meniscus lens L71 convex on the image side and a negative meniscus lens L72 convex on the image side as well as a negative meniscus lens L73 convex on the image side.

On an image plane I is disposed an imaging device (not shown) constructed from CCD, CMOS or the like.

Upon varying magnification from a wide-angle end state to a telephoto end state, the lens groups in the variable magnification optical system of the present example having the above configuration move along the optical axis so that the distance between the first lens group G1 and the second lens group G2, the distance between the second lens group G2 and the third lens group G3, the distance between the third lens group G3 and the fourth lens group G4, the distance between the fourth lens group G4 and the fifth lens group G5, the distance between the fifth lens group G5 and the sixth lens group G6, and the distance between the sixth lens group G6 and the seventh lens group G7 are varied. More specifically, the first lens group G1 moves to the image side temporarily and then to the object side. The fourth lens group G4 moves to the object side temporarily and then to the image side. The second lens group G2, the third lens group G3, the fifth lens group G5, the sixth lens group G6, and the seventh lens group G7 move to the object side.

The variable magnification optical system of the present example focuses by moving the fifth lens group G5 and the sixth lens group G6 as focusing lens groups along the optical axis. The sixth lens group G6, which is one of the focusing lens groups, is adjacent to the seventh lens group G7, which is the final lens group.

In the variable magnification optical system of the present example, the front group includes the first lens group G1, the second lens group G2, and the third lens group G3. In the variable magnification optical system of the present example, the rear group includes the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6.

In the variable magnification optical system of the present example, the lens surfaces in the final lens group having a pole are the surface on the image side of the negative meniscus lens L72 (26th surface) and the surface on the object side of the negative meniscus lens L73 (27th surface); the 26th and 27th surfaces are adjacent to each other with an air layer in between; and the 27th surface is closest to the image side. Of the negative meniscus lenses L72 and L73, which are lenses in the final lens group including a lens surface having a pole, the negative meniscus lens L73 is closest to the image side. The final lens is the negative meniscus lens L73.

Table 1 below shows specifications of the variable magnification optical system of the present example. In Table 1, fw denotes the focal length in the wide-angle end state, ft the focal length in the telephoto end state, FnoW the F-number in the wide-angle end state, FnoT the F-number in the telephoto end state, TL the shorter of the total optical length in the wide-angle end state and the total optical length in the telephoto end state, BFw the back focus in the wide-angle end state, and BFt the back focus in the telephoto end state.

In [Lens specifications], m denotes the positions of the optical surfaces counted from the object side, r the radii of curvature, d the surface-to-surface distances, nd the refractive indices for d-line (wavelength 587.6 nm), and vd the Abbe numbers for d-line. In [Lens specifications], the radius of curvature r=∞ means a plane. In [Lens specifications], the optical surfaces with “*” are aspherical surfaces.

In [Aspherical data], ASP denotes the optical surface corresponding to the aspherical data, K the conic constant, and A4 to A10 the spherical constants.

The aspherical surfaces are expressed by equation (a) below, where the height in the direction perpendicular to the optical axis is denoted by y, the distance along the optical axis from the tangent plane at the vertex of an aspherical surface to the aspherical surface at height y (a sag) by S(y), the radius of curvature of a reference sphere (paraxial radius of curvature) by r, the conic constant by K, and the n-th order aspherical coefficient by An. In the examples, the second order aspherical coefficient A2 is 0. “E-n” denotes “×10⁻ⁿ.”

S(y)=(y²/r)/{1+(1−K×y²/r²)/^1/2}+A4×y⁴+A6×y⁶+A8×y⁸+A10×y¹⁰+A12×y¹² (a)

The unit of the focal lengths f, the radii of curvature r, and the other lengths listed in Table 1 is “mm.” However, the unit is not limited thereto because the optical performance of a proportionally enlarged or reduced optical system is the same as that of the original optical system.

The above reference symbols in Table 1 will also be used similarly in the tables of the other examples described below.

TABLE 1

[General specifications]

fw
24.800

ft
67.899

FnoW
2.918

FnoT
2.919

BFw
11.754

BFt
20.313

TL
158.763

[Lens specifications]

m
r
d
nd
νd

1)
216.2097
2.900
1.69343
53.30

* 2)
29.8289
14.391

3)
307.5459
2.100
1.59349
67.00

4)
36.0228
6.545
2.00100
29.12

5)
73.1086
D5

6)
185.2739
6.802
1.81600
46.59

7)
−50.5827
1.500
1.90200
25.26

8)
−131.0353
D8

9)
39.0819
1.500
1.85000
27.03

10)
25.5513
10.624
1.59319
67.90

11)
−146.6131
D11

12)
∞
2.189
(Aperture stop)

13)
−78.2028
1.000
1.90265
35.73

14)
44.8279
0.200

15)
29.9936
2.451
1.48749
70.31

16)
47.5101
0.246

17)
40.9589
3.646
1.94595
17.98

18)
141.2376
D18

19)
45.7656
7.200
1.48749
70.31

20)
−25.4158
1.300
1.73800
32.26

21)
−114.4359
D21

22)
960.5587
4.203
1.58887
61.13

*23)
−50.4632
D23

24)
−108.3950
6.899
1.81600
46.59

25)
−24.6078
1.500
1.81930
45.76

*26)
−86.0097
5.884

*27)
−30.0456
1.500
1.58887
61.13

28)
−454.6183
BFw/BFt

[Aspherical data]

ASP: 2nd surface

K:
0.0000

A4:
2.47030E−06
A6:
1.29637E−09
A8:−8.00742E−13

A10:
1.31247E−15
A12:
−3.37400E−19

ASP: 23rd surface

K:
1.0000

A4:
1.41469E−05
A6:
−3.83973E−08
A8: 1.80756E−10

A10:
−1.29883E−13

ASP: 26th surface

K:
1.0000

A4:
5.74243E−06
A6:
9.46155E−08
A8: −7.42534E−11

A10:
−2.32790E−13

ASP: 27th surface

K:
1.0000

A4:
2.57159E−05
A6:
1.23215E−07
A8: −2.69647E−10

A10:
1.45442E−13

[Focal length data of groups]

Groups
Starting surfaces
Focal lengths

f1
1
−48.395

f2
6
105.403

f3
9
64.392

f4
13
−112.410

f5
19
134.882

f6
22
81.543

f7
24
−60.633

[Variable distance data]

W
M
T

D5
57.738
11.990
3.100

D8
1.000
4.757
1.000

D11
1.900
12.709
26.370

D18
18.418
11.653
10.584

D21
3.797
10.128
10.797

D23
2.268
4.129
2.018

W: Wide-angle end state

M: Intermediate focal length

T: Telephoto end state

FIG. 2A illustrates aberrations of the variable magnification optical system of the first example in the wide-angle end state. FIG. 2B illustrates aberrations of the variable magnification optical system of the first example in an intermediate focal length state. FIG. 2C illustrates aberrations of the variable magnification optical system of the first example in the telephoto end state.

In the graphs of aberrations, FNO and Y denote F-number and image height, respectively. More specifically, the graph of spherical aberration shows the value of F-number corresponding to the maximum aperture, the graphs of astigmatism and distortion show the maximum of image height, and the graph of coma aberration shows the value of image height. d and g denote d-line and g-line (wavelength 435.8 nm), respectively. In the graph of astigmatism, the solid lines and the broken lines show a sagittal plane and a meridional plane, respectively. The reference symbols in the graphs of aberrations of the present example will also be used in those of the other examples described below.

The graphs of aberrations suggest that the variable magnification optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

Second Example

FIG. 3 is a cross-sectional view of a variable magnification optical system of a second example.

The variable magnification optical system of the present example includes a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive refractive power, a sixth lens group G6 having positive refractive power, and a seventh lens group G7 having negative refractive power, in order from an object side. The seventh lens group G7 is a final lens group closest to an image side of the lens groups. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

The first lens group G1 consists of a positive cemented lens composed of a negative meniscus lens L11 convex on the object side and a biconvex positive lens L12 as well as a positive meniscus lens L13 convex on the object side, in order from the object side.

The second lens group G2 consists of a negative meniscus lens L21 convex on the object side, a positive cemented lens composed of a biconcave negative lens L22 and a biconvex positive lens L23, and a negative meniscus lens L24 convex on the image side, in order from the object side.

The third lens group G3 consists of a biconvex positive lens L31, a negative cemented lens composed of a biconvex positive lens L32 and a biconcave negative lens L33, and a positive meniscus lens L34 convex on the object side, in order from the object side.

The fourth lens group G4 consists of a positive cemented lens composed of a negative meniscus lens L41 convex on the object side and a biconvex positive lens L42.

The fifth lens group G5 consists of a negative meniscus lens L51 convex on the image side and a biconvex positive lens 52, in order from the object side.

The sixth lens group G6 consists of a positive meniscus lens L61 convex on the image side.

The seventh lens group G7 consists of a positive cemented lens composed of a positive meniscus lens G71 convex on the image side and a negative meniscus lens G72 convex on the image side as well as a biconcave negative lens G73, in order from the object side.

On an image plane I is disposed an imaging device (not shown) constructed from CCD, CMOS or the like.

Upon varying magnification from a wide-angle end state to a telephoto end state, the lens groups in the variable magnification optical system of the present example having the above configuration move along the optical axis so that the distance between the first lens group G1 and the second lens group G2, the distance between the second lens group G2 and the third lens group G3, the distance between the third lens group G3 and the fourth lens group G4, the distance between the fourth lens group G4 and the fifth lens group G5, the distance between the fifth lens group G5 and the sixth lens group G6, and the distance between the sixth lens group G6 and the seventh lens group G7 are varied. More specifically, the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, the fifth lens group G5, the sixth lens group G6, and the seventh lens group G7 move to the object side.

In the variable magnification optical system of the present example, the front group includes the first lens group G1 and the second lens group G2. In the variable magnification optical system of the present example, the rear group includes the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6.

In the variable magnification optical system of the present example, the lens surfaces in the final lens group having a pole are the surface on the image side of the negative meniscus lens L72 (32nd surface) and the surface on the object side of the negative lens L73 (33rd surface); the 32nd and 33rd surfaces are adjacent to each other with an air layer in between; and the 33rd surface is closest to the image side. Of the negative meniscus lens L72 and the negative lens L73, which are lenses in the final lens group including a lens surface having a pole, the negative lens L73 is closest to the image side. The final lens is the negative lens L73.

Table 2 below shows specifications of the variable magnification optical system of the present example.

TABLE 2

[General specifications]

fw
24.700

ft
117.000

FnoW
4.063

FnoT
4.066

BFw
11.455

BFt
38.827

TL
134.455

[Lens specifications]

m
r
d
nd
νd

1)
233.5776
2.000
1.85000
27.03

2)
87.6482
6.431
1.59319
67.90

3)
−959.0443
0.200

4)
60.1618
4.651
1.77250
49.62

5)
146.6456
D5

* 6)
117.5696
1.500
1.82098
42.50

7)
18.3423
6.793

8)
−54.1107
1.000
1.59319
67.90

9)
25.8545
4.820
1.85000
27.03

10)
−104.7590
1.300

11)
−35.7972
1.000
1.77250
49.62

12)
−130.0576
D12

13)
∞
2.000
(Aperture stop)

*14)
29.2194
5.294
1.55332
71.68

15)
−70.1452
1.936

16)
191.4975
3.770
1.49782
82.57

17)
−43.7144
1.000
1.95000
29.37

18)
100.0764
0.200

19)
52.3316
3.117
1.89286
20.36

20)
2501.4801
D20

21)
52.8575
1.000
1.88898
30.72

22)
19.7421
6.865
1.59319
67.90

23)
−108.3585
D23

24)
−26.4757
1.000
1.97639
21.60

25)
−41.4541
0.200

26)
178.6947
4.819
1.76043
37.84

27)
−45.8627
D27

28)
−106.6816
2.571
1.81600
46.59

*29)
−46.0714
D29

30)
−54.9936
4.015
1.79979
21.02

31)
−29.3478
1.500
1.81600
46.59

*32)
−45.2224
0.638

*33)
−36.3222
1.500
1.81951
45.71

34)
228.7540
BFw/BFt

[Aspherical data]

ASP: 6th surface

K:
1.0000

A4:
5.41835E−06
A6:
−1.00509E−08
A8:
1.79459E−11

A10:
−1.19492E−14

ASP: 14th surface

K:
1.0000

A4:
−8.73105E−06
A6:
9.15653E−09
A8:
−3.61397E−11

A10:
7.79894E−14

ASP: 29th surface

K:
1.0000

A4:
1.09444E−05
A6:
−5.46104E−09
A8:
7.47476E−12

A10:
1.54099E−14

ASP: 32nd surface

K:
1.0000

A4:
−2.47778E−06
A6:
4.98007E−08
A8:
4.30324E−10

A10:
−8.73793E−13

ASP: 33rd surface

K:
1.0000

A4:
3.23230E−06
A6:
5.85216E−08
A8:
3.47364E−10

A10:
−7.19137E−13

[Focal length data of groups]

Groups
Starting surfaces
Focal lengths

f1
1
110.518

f2
6
−20.307

f3
14
38.507

f4
21
136.085

f5
24
113.890

f6
28
97.518

f7
30
−42.419

[Variable distance data]

W
M
T

D5
2.000
28.786
42.092

D12
21.164
5.661
2.000

D20
8.937
4.555
2.000

D23
6.958
12.760
21.599

D27
2.000
10.310
9.817

D29
10.821
5.716
2.000

FIG. 4A illustrates aberrations of the variable magnification optical system of the second example in the wide-angle end state. FIG. 4B illustrates aberrations of the variable magnification optical system of the second example in an intermediate focal length state. FIG. 4C illustrates aberrations of the variable magnification optical system of the second example in the telephoto end state.

The graphs of aberrations suggest that the variable magnification optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

Third Example

FIG. 5 is a cross-sectional view of a variable magnification optical system of a third example.

The variable magnification optical system of the present example includes a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having negative refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive refractive power, and a sixth lens group G6 having negative refractive power, in order from an object side. The sixth lens group G6 is a final lens group closest to an image side of the lens groups. An aperture stop S is disposed between the third lens group G3 and the fourth lens group G4.

The first lens group G1 consists of a positive cemented lens composed of a negative meniscus lens L11 convex on the object side and a biconvex positive lens L12, in order from the object side.

The second lens group G2 consists of a negative cemented lens composed of a biconcave negative lens L21 and a positive meniscus lens L22 convex on the object side, in order from the object side.

The third lens group G3 consists of a negative meniscus lens L31 convex on the image side.

The fourth lens group G4 consists of a biconvex positive lens L41, a biconvex positive lens L42, a biconvex positive lens L43, and a negative meniscus lens L44 convex on the object side, in order from the object side.

The fifth lens group G5 consists of a biconvex positive lens L51.

The sixth lens group G6 consists of a biconvex positive lens L61, a biconcave negative lens L62, a biconvex positive lens L63, and a biconcave negative lens L64, in order from the object side.

On an image plane I is disposed an imaging device (not shown) constructed from CCD, CMOS or the like.

Upon varying magnification from a wide-angle end state to a telephoto end state, the lens groups in the variable magnification optical system of the present example having the above configuration move along the optical axis so that the distance between the first lens group G1 and the second lens group G2, the distance between the second lens group G2 and the third lens group G3, the distance between the third lens group G3 and the fourth lens group G4, the distance between the fourth lens group G4 and the fifth lens group G5, and the distance between the fifth lens group G5 and the sixth lens group G6 are varied. More specifically, the second lens group G2 and the third lens group G3 move to the image side temporarily and then to the object side. The first lens group G1, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6 move to the object side.

The variable magnification optical system of the present example focuses by moving the third lens group G3 and the fifth lens group G5 as focusing lens groups along the optical axis. The fifth lens group G5, which is one of the focusing lens groups, is adjacent to the sixth lens group G6, which is the final lens group.

In the variable magnification optical system of the present example, the lens surfaces in the final lens group having a pole are the surface on the image side of the positive lens L61 (21st surface), the surface on the object side of the negative lens L62 (22nd surface), the surfaces on the object side and on the image side of the positive lens L63 (24th and 25th surfaces), and the surface on the image side of the negative lens L64 (27th surface); the 21st and 22nd surfaces are adjacent to each other with an air layer in between; and the 27th surface is closest to the image side. Of the positive lens L61, the negative lens L62, the positive lens L63, and the negative lens L64, which are lenses in the final lens group including a lens surface having a pole, the negative lens L64 is closest to the image side. The final lens is the negative lens L64.

Table 3 below shows specifications of the variable magnification optical system of the present example.

TABLE 3

[General specifications]

fw
41.218

ft
130.898

FnoW
1.460

FnoT
2.428

BFw
10.671

BFt
37.896

TL
129.421

[Lens specifications]

m
r
d
nd
νd

* 1)
82.8316
3.000
1.89286
20.36

2)
66.9706
10.222
1.49782
82.57

3)
−242.7859
D3

* 4)
−120.1511
2.201
1.88300
40.69

* 5)
57.2914
4.785
1.92286
18.90

* 6)
354.5248
D6

* 7)
−32.5395
1.630
1.58913
61.22

* 8)
−422.5439
D8

9)
∞
1.500
(Aperture stop)

*10)
159.3869
3.156
1.88300
40.69

11)
−126.7940
0.100

*12)
57.8313
6.782
1.49782
82.57

*13)
−264.4384
0.100

14)
43.8755
7.657
1.49782
82.57

*15)
−102.4023
0.100

*16)
93.9056
1.777
1.96300
24.11

*17)
27.7244
D17

*18)
30.0338
7.496
1.49782
82.57

*19)
−52.3192
D19

*20)
463.2651
3.006
1.92286
18.90

*21)
−95.3639
0.122

*22)
−72.1888
1.433
1.58913
61.22

*23)
30.1205
4.982

*24)
49.5222
2.134
1.69350
53.20

*25)
−206.0064
1.873

*26)
−82.7023
1.500
1.74320
49.26

*27)
42.0814
BFw/BFt

[Aspherical data]

ASP: 1st surface

K:
1.0000

A4:
−2.76888E−08
A6:
−1.42190E−11
A8:
−1.51976E−15

A10:
0.00000E+00

ASP: 4th surface

K:
1.0000

A4 :
5.16437E−06 A6:
A6:
−2.54235E−09
A8:
9.97190E−14

A10:
0.00000E+00

ASP: 5th surface

K:
1.0000

A4:
2.30703E−06
A6:
3.96346E−09
A8:
−4.51403E−12

A10:
0.00000E+00

ASP: 6th surface

K:
1.0000

A4:
3.56773E−06
A6:
−1.13793E−09
A8:
−3.26259E−12

A10:
0.00000E+00

ASP: 7th surface

K:
1.0000

A4:
1.46926E−06
A6:
−5.54330E−11
A8:
1.86600E−11

A10:
0.00000E+00

ASP: 8th surface

K:
1.0000

A4:
2.27322E−06
A6:
−1.96168E−09
A8:
1.33973E−11

A10:
0.00000E+00

ASP: 10th surface

K:
1.0000

A4:
−8.46912E−06
A6:
6.18341E−10
A8:
−1.20691E−11

A10:
0.00000E+00

ASP: 12th surface

K:
1.0000

A4:
−3.35954E−06
A6:
−3.14246E−09
A8:
5.51747E−12

A10:
0.00000E+00

ASP: 13th surface

K:
1.0000

A4:
−6.60389E−06
A6:
−1.04867E−08
A8:
7.80931E−12

A10:
0.00000E+00

ASP: 15th surface

K:
1.0000

A4:
3.86065E−06
A6:
−7.71540E−09
A8:
9.20129E−12

A10:
0.00000E+00

ASP: 16th surface

K:
1.0000

A4:
3.32157−E06
A6:
−1.40119E−08
A8:
1.36738E−11

A10:
0.00000E+00

ASP: 17th surface

K:
1.0000

A4:
−9.75720E−06
A6:
−3.36474E−09
A8:
−1.21055E−11

A10:
0.00000E+00

ASP: 18th surface

K:
1.0000

A4:
−1.44803E−05
A6:
8.84782E−10
A8:
−1.49170E−11

A10:
0.00000E+00

ASP: 19th surface

K:
1.0000

A4:
3.80299E−06
A6:
−4.89754E−09
A8:
4.99904E−12

A10:
0.00000E+00

ASP: 20th surface

K:
1.0000

A4:
2.80494E−06
A6:
−1.96075E−08
A8:
1.74481E−10

A10:
0.00000E+00

ASP: 21st surface

K:
1.0000

A4:
4.06798E−06
A6:
6.38920E−09
A8:
9.23842E−11

A10:
0.00000E+00

ASP: 22nd surface

K:
1.0000

A4:
4.10047E−05
A6:
−6.58416E−08
A8:
5.69369E−11

A10:
0.00000E+00

ASP: 23rd surface

K:
1.0000

A4:
−5.63912E−06
A6:
3.45717E−08
A8:
−2.88915E−10

A10:
0.00000E+00

ASP: 24th surface

K:
1.0000

A4:
−9.53059E−05
A6:
−2.05939E−07
A8:
8.35742E−10

A10:
0.00000E+00

ASP: 25th surface

K:
1.0000

A4:
2.41063E−05
A6:
−1.80146E−07
A8:
4.31393E−10

A10:
0.00000E+00

ASP: 26th surface

K:
1.0000

A4:
7.16008E−06
A6:
6.38334E−08
A8:
−6.89847E−10

A10:
0.00000E+00

ASP: 27th surface

K:
1.0000

A4:
−9.05858E−05
A6:
1.89181E−07
A8:
−4.52460E−10

A10:
0.00000E+00

[Focal length data of groups]

Groups
Starting surfaces
Focal

f1
1
144.363

f2
4
−107.344

f3
7
−59.934

f4
10
49.980

f5
18
39.524

f6
20
−38.717

[Variable distance data]

W
M
T

D3
1.500
34.626
45.000

D6
12.713
10.569
9.851

D8
18.403
7.028
1.500

D17
10.486
11.358
13.197

D19
10.093
5.814
1.500

FIG. 6A illustrates aberrations of the variable magnification optical system of the third example in the wide-angle end state. FIG. 6B illustrates aberrations of the variable magnification optical system of the third example in an intermediate focal length state. FIG. 6C illustrates aberrations of the variable magnification optical system of the third example in the telephoto end state.

The graphs of aberrations suggest that the variable magnification optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

Fourth Example

FIG. 7 is a cross-sectional view of a variable magnification optical system of a fourth example.

The variable magnification optical system of the present example includes a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive refractive power, and a sixth lens group G6 having negative refractive power, in order from an object side. The sixth lens group G6 is a final lens group closest to an image side of the lens groups. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

The first lens group G1 consists of a negative cemented lens composed of a negative meniscus lens L11 convex on the object side and a positive meniscus lens L12 convex on the object side as well as a biconvex positive lens L13, in order from the object side.

The second lens group G2 consists of a negative meniscus lens L21 convex on the object side, a negative cemented lens composed of a biconcave negative lens L22 and a biconvex positive lens L23, and a negative meniscus lens L24 convex on the image side, in order from the object side.

The third lens group G3 consists of a biconvex positive lens L31, a negative cemented lens composed of a positive meniscus lens L32 convex on the image side and a negative meniscus lens L33 convex on the image side, a biconvex positive lens L34, and a negative cemented lens composed of a biconcave negative lens L35 and a biconvex positive lens L36, in order from the object side.

The fourth lens group G4 consists of a biconcave negative lens L41 and a biconvex positive lens L42, in order from the object side.

The fifth lens group G5 consists of a positive meniscus lens L51 convex on the image side.

The sixth lens group G6 consists of a positive cemented lens composed of a positive meniscus lens L61 convex on the image side and a negative meniscus lens L62 convex on the image side as well as a negative meniscus lens L63 convex on the image side, in order from the object side.

On an image plane I is disposed an imaging device (not shown) constructed from CCD, CMOS or the like.

Upon varying magnification from a wide-angle end state to a telephoto end state, the lens groups in the variable magnification optical system of the present example having the above configuration move along the optical axis so that the distance between the first lens group G1 and the second lens group G2, the distance between the second lens group G2 and the third lens group G3, the distance between the third lens group G3 and the fourth lens group G4, the distance between the fourth lens group G4 and the fifth lens group G5, and the distance between the fifth lens group G5 and the sixth lens group G6 are varied. More specifically, the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6 move to the object side.

The variable magnification optical system of the present example focuses by moving the fourth lens group G4 and the fifth lens group G5 as focusing lens groups along the optical axis. The fifth lens group G5, which is one of the focusing lens groups, is adjacent to the sixth lens group G6, which is the final lens group.

In the variable magnification optical system of the present example, the lens surfaces in the final lens group having a pole are the surface on the image side of the negative meniscus lens L62 (32nd surface) and the surface on the object side of the negative meniscus lens L63 (33rd surface); the 32nd and 33rd surfaces are adjacent to each other with an air layer in between; and the 33rd surface is closest to the image side. Of the negative meniscus lenses L62 and L63, which are lenses in the final lens group including a lens surface having a pole, the negative meniscus lens L63 is closest to the image side. The final lens is the negative meniscus lens L63.

Table 4 below shows specifications of the variable magnification optical system of the present example.

TABLE 4

[General specifications]

fw
24.700

ft
67.900

FnoW
3.534

FnoT
5.704

BFw
11.454

BFt
37.762

TL
128.454

[Lens specifications]

m
rd
nd
νd

1)
1117.9689
2.000
1.85000
27.03

2)
151.6754
6.000
1.59319
67.90

3)
604.3570
0.200

4)
95.1148
6.000
1.80400
46.60

5)
−3888.8614
D5

* 6)
77.0311
1.500
1.82098
42.50

7)
18.3277
10.191

8)
−39.8674
1.000
1.59319
67.90

9)
32.2316
3.964
1.85000
27.03

10)
−160.4566
2.810

11)
−20.7240
1.000
1.77250
49.62

12)
−26.4134
D12

13)
∞
2.000
(Aperture stop)
2.000

*14)
25.9174
3.517
1.55332
71.68

15)
−106.0252
2.266

16)
−37.8522
3.006
1.49782
82.57

17)
−18.6967
1.000
1.95000
29.37

18)
−26.7934
0.553

19)
35.6642
3.342
1.89286
20.36

20)
−191.1865
3.584

21)
−146.6275
1.000
1.92643
24.50

22)
14.7466
4.904
1.59319
67.90

23)
−120.3128
D23

24)
−51.116
51.000
1.98283
26.42

25)
737.3403
4.356

26)
42.3632
5.569
1.72907
37.37

27)
−71.7670
D27

28)
−133.5324
1.826
1.81932
45.76

*29)
−70.5109
D29

30)
−36.9754
4.433
1.83984
19.98

31)
−22.5369
1.500
1.86211
37.55

*32)
−32.1387
1.139

*33)
−25.0000
1.500
1.83552
42.13

34)
−73.1491
BFw/BFt

[Aspherical data]

ASP: 6th surface

K:
1.0000

A4:
4.42790E−06
A6:
−4.84239E−10
A8:
−9.10319E−12

A10:
3.51555E−14

ASP: 14th surface

K:
1.0000

A4 :
−7.97690E−06
A6:
−4.21779E−09
A8:
1.20186E−10

A10:
−6.81333E−13

ASP: 29th surface

K:
1.0000

A4 :
1.49515E−05
A6:
−1.13726E−08
A8:
4.96744E−11

A10:
−1.20573E−13

ASP: 32nd surface

K:
1.0000

A4:
1.46066E−05
A6:
7.69919E−08
A8:
3.39086E−10

A10:
−9.94878E−13

ASP: 33rd surface

K:
1.0000

A4:
2.64437E−05
A6:
7.82319E−08
A8:
2.81284E−10

A10:
−8.35503E−13

[Focal length data of groups]

Groups
Starting surfaces
Focal lengths

f1
1
147.795

f2
6
−21.765

f3
14
28.551

f4
21
104.520

f5
24
180.000

f6
28
−55.064

[Variable distance data]

W
M
T

D5
2.000
17.953
24.917

D12
18.868
5.788
2.000

D24
5.964
8.699
10.664

D28
2.000
4.108
5.039

D30
7.009
4.668
3.540

FIG. 8A illustrates aberrations of the variable magnification optical system of the fourth example in the wide-angle end state. FIG. 8B illustrates aberrations of the variable magnification optical system of the fourth example in an intermediate focal length state. FIG. 8C illustrates aberrations of the variable magnification optical system of the fourth example in the telephoto end state.

The graphs of aberrations suggest that the variable magnification optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

Fifth Example

FIG. 9 is a cross-sectional view of a variable magnification optical system of a fifth example.

The variable magnification optical system of the present example includes a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power, in order from an object side. The fourth lens group G4 is a final lens group closest to an image side of the lens groups. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

The third lens group G3 consists of a biconvex positive lens L31, a positive cemented lens composed of a positive meniscus lens L32 convex on the image side and a negative meniscus lens L33 convex on the image side, a biconvex positive lens L34, a negative cemented lens composed of a negative meniscus lens L35 convex on the object side and a positive meniscus lens L36 convex on the object side, a biconcave negative lens L37, a biconvex positive lens L38, and a positive meniscus lens L39 convex on the image side, in order from the object side.

The fourth lens group G4 consists of a positive cemented lens composed of a positive meniscus lens L41 convex on the image side and a negative meniscus lens L42 convex on the image side as well as a negative meniscus lens L43 convex on the image side, in order from the object side.

On an image plane I is disposed an imaging device (not shown) constructed from CCD, CMOS or the like.

The variable magnification optical system of the present example focuses by moving the negative lens L37, the positive lens L38, and the positive meniscus lens L39 in the third lens group G3 along the optical axis.

In the variable magnification optical system of the present example, the lens surfaces in the final lens group having a pole are the surface on the image side of the negative meniscus lens L42 (32nd surface) and the surface on the object side of the negative meniscus lens L43 (33rd surface); the 32nd and 33rd surfaces are adjacent to each other with an air layer in between; and the 33rd surface is closest to the image side. Of the negative meniscus lenses L42 and L43, which are lenses in the final lens group including a lens surface having a pole, the negative meniscus lens L43 is closest to the image side. The final lens is the negative meniscus lens L43.

Table 5 below shows specifications of the variable magnification optical system of the present example.

TABLE 5

[General specifications]

fw
24.699

ft
67.894

FnoW
3.183

FnoT
5.856

BFw
11.452

BFt
45.888

TL
128.452

[Lens specifications]

m
r
d
nd
νd

1)
1079.5916
2.000
1.85000
27.03

2)
131.0401
4.000
1.59319
67.90

3)
250.0000
0.200

4)
150.0000
6.006
1.80400
46.60

5)
−348.2905
D5

* 6)
58.0611
1.500
1.82098
42.50

7)
19.6123
14.025

8)
−29.0748
1.000
1.59319
67.90

9)
31.5055
8.443
1.85000
27.03

10)
−106.9081
2.211

11)
−22.1747
1.000
1.77250
49.62

12)
−31.3884
D12

13)
∞
2.000
(Aperture stop)

*14)
25.4805
4.020
1.55332
71.68

15)
−113.5173
2.153

16)
−239.9198
3.891
1.49782
82.57

17)
−22.1721
1.000
1.95000
29.37

18)
−39.0858
0.200

19)
52.2652
2.726
1.89286
20.36

20)
−1068.6197
2.000

21)
49.5620
1.000
1.84986
29.09

22)
13.5449
4.613
1.59319
67.90

23)
75.8355
9.162

24)
−64.9984
1.000
1.98765
23.25

25)
98.0551
1.159

26)
42.6108
4.661
1.66696
26.88

27)
−59.111
62.260

28)
−676.8447
2.263
1.48749
70.32

*29)
−62.6788
D29

30)
−42.7013
5.543
1.70633
24.58

31)
−17.9430
1.500
1.89105
33.79

*32)
−34.7690
1.119

*33)
−26.5315
1.500
1.88300
40.69

34)
−82.1646
BFw/BFt

[Aspherical data]

ASP: 6th surface

K:
1.0000

A4:
3.37459E−06
A6:
−1.04691E−09
A8:
1.98567E−12

A10:
6.24320E−15

ASP: 14th surface

K:
1.0000

A4:
−1.13875E−05
A6:
4.02722E−09
A8:
9.68479E−12

A10:
−6.13774E−14

ASP: 29th surface

K:
1.0000

A4:
2.17948E−05
A6:
−1.90983E−08
A8:
1.44726E−10

A10:
−5.65784E−13

ASP: 32nd surface

K:
1.0000

A4:
1.48261E−05
A6:
8.77718E−08
A8:
2.97989E−10

A10:
−9.31413E−13

ASP: 33rd surface

K:
1.0000

A4:
2.17627E−05
A6:
8.04358E−08
A8:
2.99418E−10

A10:
−8.62499E−13

[Focal length data of groups]

Groups
Starting surfaces
Focal lengths

f1
1
242.287

f2
6
−21.345

f4
30
−42.099

[Variable distance data]

W
M
T

D5
2.000
22.941
28.574

D12
15.558
5.125
2.000

D2 9
5.287
4.827
4.760

FIG. 10A illustrates aberrations of the variable magnification optical system of the fifth example in the wide-angle end state. FIG. 10B illustrates aberrations of the variable magnification optical system of the fifth example in an intermediate focal length state. FIG. 10C illustrates aberrations of the variable magnification optical system of the fifth example in the telephoto end state.

The graphs of aberrations suggest that the variable magnification optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

A small-sized variable magnification optical system of favorable optical performance can be achieved according to the above examples.

The following are a list of the conditional equations and the values for the conditional equations in the examples.

fF denotes the focal length of the focusing lens group adjacent to the final lens group, and fR denotes the focal length of the final lens group. fRI denotes the focal length of a lens in the final lens group including a lens surface having a pole. k denotes the height of the pole from an optical axis, h denotes the effective radius of the lens surface having a pole. νR denotes the Abbe number of one of lenses in the final lens group including a lens surface having a pole, and νR1 denotes the Abbe number of a lens closest to the image side of lenses in the final lens group including a lens surface having a pole.

[List of conditional equations]

(1)
TL/fw

(2)
fRI/fR

(3)
fF/fR

(4)
fRI/fw

(5) (6)
k/h

(7)
BFw/fw

(8)
vR

(9)
vR1

[Values for conditional equations]

Example 1
Example 2
Example 3
Example 4
Example 5

(1)
6.402
5.444
3.140
5.201
5.201

(2)
0.902
0.899
0.964
0.837
1.068

0.702
2.522
−1.492,
1.713
1.032

0.927,

−2.219

(3)
1.345
2.299
1.021
3.269
3.362

(4)
2.206,
1.545,
0.906,
1.867,
1.820,

1.715
4.322
1.402,
3.819
1.759

0.871,

2.084

(5) (6)
0.803,
0.858,
0.565,
0.860,
0.960,

0.728
0.850
0.980,
0.832
0.893

0.496,

0.736,

0.979

(7)
0.474
0.464
0.259
0.464
0.464

(8)
61.13,
45.71,
49.26,
42.13,
40.69,

45.76
46.59
53.20,
37.55
33.79

61.22,

18.90

(9)
61.13
45.71
49.26
42.13
40.69

The above examples illustrate specific examples of the present invention, and the present invention is not limited thereto. The following details can be appropriately employed unless the optical performance of the variable magnification optical system of the embodiment of the present application is lost.

The lens surfaces of the lenses constituting any of the variable magnification optical systems of the above examples may be covered with antireflection coating having high transmittance in a wide wavelength range. This reduces flares and ghosts, and enables achieving optical performance with high contrast.

Next, a camera including the variable magnification optical system of the present embodiment is described with reference to FIG. 11.

FIG. 11 schematically illustrates a camera including the variable magnification optical system of the present embodiment.

The camera 1 is a “mirror-less camera” of an interchangeable lens type including the variable magnification optical system according to the first example as an imaging lens 2.

In the camera 1, light from an object (subject) (not shown) is condensed by the imaging lens 2, and reaches an imaging device 3. The imaging device 3 converts the light from the subject to image data.

When a release button (not shown) is pressed by a photographer, the image data is stored in a memory (not shown). In this way, the photographer can take a picture of the subject with the camera 1.

The variable magnification optical system of the first example mounted on the camera 1 as the imaging lens 2 is a small-sized variable magnification optical system of favorable optical performance. Thus the camera 1 can be small and achieve favorable optical performance. When a camera is configured by including any one of the variable magnification optical systems of the second to fifth examples as the imaging lens 2, the camera can have the same effect as the camera 1.

Finally, a method for manufacturing a variable magnification optical system of the present embodiment is briefly described with reference to FIG. 12.

FIG. 12 is a schematic flowchart of a method for manufacturing a variable magnification optical system of the present embodiment.

The method for manufacturing a variable magnification optical system of the present embodiment shown in FIG. 12 is a method for manufacturing a variable magnification optical system including a plurality of lens groups, and includes the following steps S1, S2, S3, and S4:

Step S1: preparing Lens groups one of which includes a lens surface having a pole;

Step S2: arranging the lens groups so that upon varying magnification the distances between the lens groups are varied;

Step S3: arranging so that a final lens group closest to an image side of the lens groups includes at least one lens including a lens surface having a pole; and

Step S4: arranging so that the variable magnification optical system satisfies the following conditional equation (1):

0.50<TL/fw<10.00 (1)

where

TL denotes the shorter of the total optical length in a wide-angle end state and the total optical length in a telephoto end state of the variable magnification optical system, and

fw denotes the focal length of the variable magnification optical system in the wide-angle end state.

A small-sized variable magnification optical system of favorable optical performance can be manufactured by the method for manufacturing a variable magnification optical system of the present embodiment.

Note that those skilled in the art can make various changes, substitutions, and modifications without departing from the spirit and scope of the present invention.

REFERENCE SIGNS LIST

- S aperture stop
- I image plane
- 1 camera
- 2 imaging lens
- 3 imaging device

Number	Date	Country	Kind
2020-012564	Jan 2020	JP	national
2020-012573	Jan 2020	JP	national

VARIABLE MAGNIFICATION OPTICAL SYSTEM, OPTICAL APPARATUS, AND METHOD FOR MANUFACTURING VARIABLE MAGNIFICATION OPTICAL SYSTEM

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