JP2016139087A - Imaging optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system that offers extremely small distortion aberration, a halt view angle of 43 degrees or greater, a back focus of approximately 1.2-1.4 times a focal length, good optical performance, and high-speed focusing capability.SOLUTION: An imaging optical system comprises a first lens group G1 having negative refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power and including an aperture stop S in order from the object side, and is configured such that the second lens group G2 is moved toward the object side along an optical axis when shifting focus from infinity to a close distance. The imaging optical system satisfies predefined conditional expressions.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging optical system suitable for a photographing lens used in a digital camera, a video camera, or the like.

  2. Description of the Related Art Conventionally, an interchangeable lens photographing apparatus generally has an optical viewfinder. Therefore, since it is necessary to arrange a mirror for guiding the light beam to the finder optical system between the imaging optical system and the image sensor, a long back focus is required. Therefore, a wide-angle lens is generally a retrofocus type that can ensure a back focus longer than the focal length as described in Patent Document 1.

  However, in recent years, a so-called mirrorless camera has appeared that can exchange lenses by using an electronic viewfinder that can transfer an image directly from the image sensor to the viewfinder. Since the mirrorless camera can omit the mirror to guide the light beam to the viewfinder optical system, it is possible to shorten the back focus of the taking lens, and it is necessary to make it an extreme retrofocus type even for wide-angle lenses. Absent. In addition, the focal length can be further shortened. (For example, patent document 2 is mentioned.)

JP-A-8-110467 JP 2012-173435 A

  In a retrofocus type imaging optical system, it is known that it is difficult to correct distortion well. The imaging optical system described in Patent Document 1 has a strong tendency for a retrofocus type in order to ensure a long back focus. Therefore, there is a problem that correction of distortion is insufficient.

  Although the imaging optical system of Patent Document 2 does not ensure a long back focus, the distortion aberration is still insufficiently corrected. If an attempt is made to shorten the focal length while maintaining the current back focus, the retrofitting is not possible. There is a problem that the tendency of the focus type must be strengthened, and further deterioration of distortion is inevitable. Further, in the imaging optical system of Patent Document 2, the first lens group having negative refractive power is composed of a negative lens and a positive lens, and only the first lens group has an effect of canceling chromatic aberration. The third lens group must have the effect of canceling out chromatic aberration, and it is necessary to increase the refractive power of each positive and negative lens for achromatization. There was a problem that became difficult.

  The present invention has been made in view of such a situation, and has an extremely small amount of distortion, an optical half-field angle of 43 degrees or more, and a back focus of about 1.2 to 1.4 times the focal length. It is an object of the present invention to provide an imaging optical system having good performance and capable of rapid focusing.

The first invention, which is a means for solving the above-mentioned problems, includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and an aperture stop S. Is configured to move the second lens group G2 along the optical axis toward the object side during focusing from infinity to a short distance. An imaging optical system characterized by satisfying the following conditional expression:
(1) vdLA> 70.0
(2) 0.80 <| f12 / f | <1.40
vdLA: Maximum Abbe number of the negative meniscus lens constituting the first lens group G1 with respect to the d-line f12: Combined focal length f1 of the first lens group G1 and the second lens group G2 at infinity Focal length at infinity in the system

  The second invention, which is means for solving the above-mentioned problems, is the imaging optical system according to the first invention, and the second lens group G2 is a single lens or a set of units. An imaging optical system configured.

  A third invention, which is a means for solving the above-mentioned problems, is an imaging optical system according to the first invention or the second invention, and the first lens group G1 is disposed on the object side. This is an imaging optical system composed only of a negative meniscus lens having a convex surface.

  A fourth invention, which is means for solving the above-mentioned problems, is an imaging optical system according to any one of the first to third inventions, and the first lens group G1 further includes: This is an imaging optical system composed of two negative meniscus lenses having a convex surface facing the object side.

  According to the present invention, the distortion is extremely small, the half angle of view is 43 degrees or more, the optical performance of the back focus is about 1.2 to 1.4 times the focal length, and quick focusing is possible. An imaging optical system can be provided.

It is a lens block diagram in the infinite distance which concerns on Example 1 of the imaging optical system of this invention. FIG. 6 is a longitudinal aberration diagram of the imaging optical system of Example 1 at an imaging distance of infinity. FIG. 6 is a longitudinal aberration diagram of the imaging optical system of Example 1 at a shooting distance of 200 mm. FIG. 3 is a lateral aberration diagram at the photographing distance infinite for the imaging optical system according to Example 1. 3 is a lateral aberration diagram at the photographing distance 200 mm of the imaging optical system of Example 1. FIG. It is a lens block diagram in the infinite distance which concerns on Example 2 of the imaging optical system of this invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance infinity of the imaging optical system according to Example 2. 6 is a longitudinal aberration diagram of the imaging optical system of Example 2 at a shooting distance of 200 mm. FIG. 6 is a lateral aberration diagram at an imaging distance infinite for the imaging optical system of Example 2. FIG. FIG. 6 is a lateral aberration diagram at the photographing distance 200 mm in the imaging optical system according to Example 2. It is a lens block diagram in the infinite distance which concerns on Example 3 of the imaging optical system of this invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance infinite for the imaging optical system according to Example 3. FIG. 6 is a longitudinal aberration diagram of the imaging optical system of Example 3 at a shooting distance of 200 mm. FIG. 6 is a lateral aberration diagram at an imaging distance infinite for the imaging optical system according to Example 3. 6 is a lateral aberration diagram at the photographing distance 200 mm of the imaging optical system of Example 3. FIG. It is a lens block diagram in the infinite distance which concerns on Example 4 of the imaging optical system of this invention. FIG. 10 is a longitudinal aberration diagram at an imaging distance infinite for the imaging optical system according to Example 4; FIG. 6 is a longitudinal aberration diagram of the imaging optical system of Example 4 at a shooting distance of 200 mm. FIG. 6 is a lateral aberration diagram at an imaging distance infinite for the imaging optical system according to Example 4. 6 is a lateral aberration diagram at the photographing distance of 200 mm in the imaging optical system of Example 4. FIG.

The imaging optical system according to the present invention has, as the first invention, negative refraction in order from the object side, as can be seen from the lens configuration diagrams of the embodiments of the present invention shown in FIGS. 1, 6, 11, and 16. A first lens group G1 having a power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power including an aperture stop S. An imaging optical system satisfying the following conditional expression, wherein the second lens group G2 is moved to the object side along the optical axis during focusing.
(1) vdLA> 70.0
(2) 0.80 <| f12 / f | <1.40
vdLA: Maximum Abbe number of the negative meniscus lens constituting the first lens group G1 with respect to the d-line f12: Combined focal length f1 of the first lens group G1 and the second lens group G2 at infinity Focal length at infinity in the system

  First, the refractive power arrangement of the first lens group G1, the second lens group G2, and the third lens group G3 will be described. The imaging optical system of the present invention includes a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power. By adopting a retrofocus type refracting power arrangement consisting of the above, it is possible to cope with a lens interchangeable camera while being a wide angle lens having a half angle of view of 43 degrees or more.

  In the imaging optical system according to the present invention, since the first lens group G1 has a negative refractive power, the distortion occurring in a large under-periphery in the first lens group G1 as compared with the vicinity of the lens center. In this case, a negative meniscus aspheric lens whose refractive power is weakened is arranged to correct it appropriately.

In the present invention, the distortion at the time of photographing at infinity is expressed by the calculation formula (A). In the present invention, the difference between the maximum value and the minimum value of the distortion aberration D from the optical axis to the maximum image height is corrected properly within 1%.
(A) D = (Y−y0) / y0 * 100 [%]
D: Distortion aberration Y: Actual image height y0: Reasonable height

  Conditional expression (1) defines the maximum Abbe number for the d-line of the negative meniscus lens constituting the first lens group G1. By defining the maximum Abbe number for the d-line of the negative meniscus lens constituting the first lens group G1, a preferable range for suppressing lateral chromatic aberration is defined.

  When the lower limit of conditional expression (1) is exceeded, the refractive index difference of each wavelength of the negative meniscus lens becomes large. That is, the dispersion becomes large, and it becomes difficult to correct the lateral chromatic aberration well.

  In addition, regarding the conditional expression (1) described above, the lower limit value is further limited to 80.0, so that the above-described effect can be further ensured and effective for correcting chromatic aberration of the secondary spectrum.

  Conditional expression (2) defines the ratio of the combined focal length f12 of the first lens group G1 and the second lens group G2 at infinity to the focal length f of the entire lens system at infinity. . By satisfying conditional expression (2), the proper back aberration and the distance between the second lens group G2 and the third lens group G3 are appropriate, and the proper lens aberration is maintained while preventing the lens from becoming too long. Is possible.

  When the upper limit of conditional expression (2) is exceeded, the back focus is shortened, but the focal length f3 of the third lens group G3 is increased, and the distance between the second lens group G2 and the third lens group G3 is increased. Increases the overall length.

  If the lower limit of conditional expression (2) is exceeded, the refractive power of the combined focal length f12 of the first lens group G1 and the second lens group G2 will become strong, and the occurrence of distortion will increase. As a result, it becomes difficult to correct distortion.

  In the above-described conditional expression (2), a more preferable effect can be expected by further limiting the lower limit value to 0.90 and further limiting the upper limit value to 1.30.

  Furthermore, regarding the conditional expression (2) described above, the above-mentioned effect can be further ensured by further limiting the lower limit value to 0.95 and further limiting the upper limit value to 1.10.

  The imaging optical system according to the second invention is the first invention, and it is desirable that the second lens group G2 is constituted by a single lens or a set of units. However, a unit refers to a lens group that moves in the same way during focusing.

  Since the second lens group G2 is configured to move toward the object side along the optical axis during focusing from infinity to a short distance, it is desirable that the focus group be lightweight. If the focus group is lightweight, not only quick focusing can be performed, but also the actuator for moving the focus lens can be made smaller.

  The imaging optical system according to the third invention is the first or second invention, and the first lens group G1 is preferably composed only of a negative meniscus lens having a convex surface facing the object side. .

  In the case of a retro-focus type wide-angle lens, the light beam height of the off-axis light beam incident on the first lens group is much higher than the light beam height of the axial light beam. Therefore, the light beam of the off-axis light beam is strongly subjected to the downward bending action, so that negative distortion is increased. Therefore, considering the lens shape so that the incident angle of off-axis rays to the first lens group and the declination angle of the first lens group are reduced, the first lens group is only a negative meniscus lens having a convex surface facing the object side. It is optimal to be configured, and the occurrence of aberrations such as distortion can be suppressed, contributing to optical performance.

  Further, the imaging optical system according to a fourth aspect of the present invention is any one of the first to third aspects, wherein the first lens group G1 includes two negative meniscus lenses having a convex surface facing the object side. It is desirable that

  Furthermore, by using two negative meniscus lenses, it is possible to further suppress distortion by further optimizing the incident angle of off-axis rays to the first lens group and the declination angle of the first lens group. it can. Although it is possible to reduce the occurrence of distortion by inserting a positive lens closer to the image plane than the negative meniscus lens of the first lens group G1, the height of the off-axis light beam incident on the positive lens and the on-axis light beam can be reduced. The difference in beam height is smaller than the difference between the beam height of the off-axis light beam incident on the negative meniscus lens and the light beam height of the on-axis light beam, so that the negative lens causes negative distortion due to the positive lens effect. In the case of a small beam, the positive lens effect is stronger than the negative meniscus lens effect in the vicinity of the center, and a large positive distortion occurs only at the intermediate angle of view. Therefore, it is not preferable to insert a positive lens in the first lens group G1 for the purpose of suppressing the occurrence of distortion.

  Next, a lens configuration of an example according to the imaging optical system of the present invention will be described. In the following description, the lens configuration is described in order from the object side to the image side.

  In [Surface data], the surface number is the number of the lens surface or aperture stop counted from the object side, r is the radius of curvature of each surface, d is the distance between the surfaces, nd is the refractive index with respect to the d-line (wavelength 587.56 nm). , Vd represents the Abbe number of the d line, and the effective radius represents the ray height.

  The * (asterisk) attached to the surface number indicates that the lens surface shape is an aspherical surface. Further, BF represents back focus, and the object surface distance represents the distance from the subject to the lens first surface.

  The (diaphragm) attached to the surface number indicates that the aperture stop S is located at that position, and (flare cut) indicates that the flare cut F is located at that position. In addition, ∞ (infinity) is written in the radius of curvature with respect to the plane, the aperture stop S or the flare cut F.

[Aspherical data] indicates an aspherical coefficient that gives the aspherical shape of the lens surface marked with * in [Surface data]. The shape of the aspheric surface is y for the displacement from the optical axis in the direction perpendicular to the optical axis, z for the displacement (sag amount) from the intersection of the aspheric surface and the optical axis in the optical axis direction, and r for the radius of curvature of the reference spherical surface. When the conic coefficient is K, 4, 6, 8, and the 10th-order aspheric coefficient is A4, A6, A8, and A10, the coordinates of the aspheric surface are expressed by the following equations.

  [Various data] shows values such as the focal length in each focal length state.

  [Variable interval data] indicates the value of the variable interval and BF (back focus) in each focal length state.

  [Lens Group Data] indicates the surface number of the most object side constituting each lens group and the combined focal length of the entire group.

  In the aberration diagrams corresponding to each example, d, g, and C represent d-line, g-line, and C-line, respectively, and ΔS and ΔM represent sagittal image plane and meridional image plane, respectively. .

  Further, in the lens configuration diagrams shown in FIGS. 1, 6, 11, and 16, I is the image plane, and the alternate long and short dash line passing through the center is the optical axis.

  In all the values of the following specifications, the focal length f, the radius of curvature r, the lens surface interval d, and other length units described are in millimeters (mm) unless otherwise specified. In the system, the same optical performance can be obtained even in proportional expansion and proportional reduction, and the present invention is not limited to this.

  FIG. 1 is a lens configuration diagram of an imaging optical system according to Example 1 of the present invention. In order from the object side, the lens unit includes a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 has a negative refractive power as a whole, and the first lens group G1 A negative meniscus lens L1a having a convex surface facing the object side and a negative meniscus lens L1b having a convex surface facing the object side, both lens surfaces of the negative meniscus lens L1a have a predetermined aspherical shape.

  The second lens group G2 has a negative refractive power as a whole, and is composed of a biconcave negative lens L2a.

  The third lens group G3 has a positive refractive power as a whole, and includes two lenses, an aperture stop S, a negative meniscus lens L3a having a convex surface facing the object side, and a biconvex positive lens L3b. A cemented lens composed of two lenses, a cemented lens, a flare cut F, a biconvex positive lens L3c, a negative meniscus lens L3d having a convex surface facing the object side, and a biconvex positive lens L3e; A negative meniscus lens L3h including a cemented lens including two lenses, a convex positive lens L3f and a negative meniscus lens L3g having a concave surface facing the object side, and a negative meniscus lens L3h having a concave surface facing the object side. The image-side lens surface has a predetermined aspherical shape.

  The second lens group G2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

Subsequently, specification values of the imaging optical system according to Example 1 are shown below.
Numerical example 1
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 * 24.3233 2.0000 1.58913 61.25
2 * 10.8623 5.5093
3 20.9206 1.2000 1.49700 81.60
4 11.4711 (d4)
5 -68.6637 1.0000 1.43700 95.10
6 316.0852 (d6)
7 (Aperture) ∞ 2.6501
8 37.9119 0.8000 1.59282 68.62
9 10.6710 3.8497 1.51680 64.19
10 -36.9412 3.3000
11 (flare cut) ∞ 2.4648
12 22.5426 3.4623 1.43700 95.10
13 -728.6284 3.1921
14 106.0910 2.0067 1.58144 40.89
15 20.7523 5.9354 1.43700 95.10
16 -20.7523 2.5257
17 38.7382 5.5152 1.43700 95.10
18 -15.7572 0.7500 1.88300 40.80
19 -70.3393 2.5105
20 -31.8947 1.1000 1.80610 40.73
21 * -57.6037 (BF)
Image plane ∞

[Aspherical data]
1 side 2 side 21 side
K 0.00000 -1.00000 0.00000
A4 -3.75518E-05 5.90593E-07 3.90101E-05
A6 4.36935E-08 -9.34038E-08 2.80426E-08
A8 -5.91274E-11 -3.08947E-11 5.23922E-10
A10 0.00000E + 00 0.00000E + 00 1.35285E-13

[Various data]
INF 200mm
Focal length 13.98 13.28
F number 3.53 3.54
Full angle of view 2ω 90.74 92.90
Statue height Y 14.20 14.20
Total lens length 89.25 89.25

[Variable interval data]
INF 200mm
d0 110.7500
d4 17.5523 13.0242
d6 4.3541 8.8822
BF 17.5750 17.5750

[Lens group data]
Group Start surface Focal length
G1 1 -19.82
G2 5 -128.98
G12 1 -15.13
G3 7 20.57

  FIG. 6 is a lens configuration diagram of the imaging optical system according to Example 2 of the present invention. In order from the object side, the lens unit includes a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 has a negative refractive power as a whole, and the first lens group G1 A negative meniscus lens L1a having a convex surface facing the object side and a negative meniscus lens L1b having a convex surface facing the object side, both lens surfaces of the negative meniscus lens L1a have a predetermined aspherical shape.

  The second lens group G2 has a negative refractive power as a whole, and is composed of a biconcave negative lens L2a.

  The third lens group G3 has a positive refractive power as a whole, and includes two lenses, an aperture stop S, a negative meniscus lens L3a having a convex surface facing the object side, and a biconvex positive lens L3b. A cemented lens including a cemented lens, a flare cut F, a positive meniscus lens L3c having a convex surface facing the object side, a negative meniscus lens L3d having a convex surface facing the object side, and a biconvex positive lens L3e. A lens, a cemented lens composed of two lenses, a biconvex positive lens L3f and a negative meniscus lens L3g having a concave surface facing the object side, and a negative meniscus lens L3h having a concave surface facing the object side, The lens surface on the image side of the negative meniscus lens L3h has a predetermined aspherical shape.

  The second lens group G2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

Subsequently, specification values of the imaging optical system according to Example 2 are shown below.
Numerical example 2
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 * 23.0837 2.0000 1.58313 59.46
2 * 9.0102 3.1875
3 16.1661 1.2000 1.49700 81.60
4 10.5125 (d4)
5 -200.0000 1.0000 1.43700 95.10
6 77.0673 (d6)
7 (Aperture) ∞ 2.6974
8 33.1050 0.8000 1.59282 68.62
9 9.9000 3.5521 1.51680 64.19
10 -29.6381 3.3000
11 (flare cut) ∞ 1.4753
12 18.5751 3.1373 1.43700 95.10
13 202.4366 3.3777
14 68.6065 1.4048 1.83481 42.72
15 18.8114 4.7258 1.43700 95.10
16 -18.8114 2.6357
17 40.1618 4.7212 1.43700 95.10
18 -15.6140 0.7500 1.88300 40.80
19 -62.2753 2.5693
20 -27.7936 1.1000 1.80610 40.73
21 * -47.8074 (BF)
Image plane ∞

[Aspherical data]
1 side 2 side 21 side
K 0.00000 -1.00000 0.00000
A4 -3.96887E-05 3.35668E-05 4.27783E-05
A6 2.94290E-08 -1.00793E-07 8.80624E-08
A8 -5.15347E-11 -1.13985E-09 3.92712E-10
A10 0.00000E + 00 0.00000E + 00 2.22145E-12


[Various data]
INF 200mm
Focal length 13.97 13.28
F number 4.13 4.13
Full angle of view 2ω 90.90 92.68
Statue height Y 14.20 14.20
Total lens length 82.60 82.60

[Variable interval data]
INF 200mm
d0 117.4043
d4 16.7970 12.9201
d6 4.4772 8.3541
BF 17.6874 17.6874

[Lens group data]
Group Start surface Focal length
G1 1 -18.01
G2 5 -127.16
G12 1 -13.96
G3 7 19.33

  FIG. 11 is a lens configuration diagram of the imaging optical system according to Example 3 of the present invention. In order from the object side, the lens unit includes a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 has a negative refractive power as a whole, and the first lens group G1 A negative meniscus lens L1a having a convex surface facing the object side and a negative meniscus lens L1b having a convex surface facing the object side, both lens surfaces of the negative meniscus lens L1a have a predetermined aspherical shape.

  The second lens group G2 has a negative refractive power as a whole, and is composed of a negative meniscus lens L2a having a concave surface directed toward the object side.

  The third lens group G3 has a positive refractive power as a whole. The third lens group G3 includes a flare cut F, an aperture stop S, a negative meniscus lens L3a having a convex surface facing the object side, and a biconvex positive lens L3b. A cemented lens composed of two lenses, a cemented lens composed of a single lens, a positive meniscus lens L3c with a concave surface facing the object side, a negative meniscus lens L3d with a convex surface facing the object side, and a biconvex positive lens L3e An image of a biconvex positive lens L3b including a lens and a cemented lens including two lenses, a positive meniscus lens L3f having a concave surface facing the object side and a negative meniscus lens L3g having a concave surface facing the object side. The lens surface on the side has a predetermined aspherical shape.

  The second lens group G2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

Subsequently, specification values of the imaging optical system according to Example 3 are shown below.
Numerical Example 3
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 * 23.0082 2.0000 1.58913 61.25
2 * 10.5500 3.5667
3 20.5747 1.2000 1.49700 81.60
4 11.2177 (d4)
5 -48.2096 0.8000 1.49700 81.60
6 -643.3350 (d6)
7 (flare cut) ∞ 3.7000
8 (Aperture) ∞ 0.8327
9 16.4396 1.5000 1.77250 49.62
10 12.2389 2.7713 1.59201 67.02
11 * -129.3729 4.2553
12 -68.5672 2.4013 1.72916 54.67
13 -18.8724 2.6683
14 104.2574 0.8500 1.88300 40.80
15 13.9002 4.3051 1.43700 95.10
16 -29.9419 4.2847
17 -229.8410 5.1989 1.43700 95.10
18 -11.2967 0.8500 1.80611 40.73
19 -28.7754 (BF)
Image plane ∞

[Aspherical data]
1 side 2 side 11 side
K 0.00000 -1.00000 0.00000
A4 6.16610E-06 6.15401E-05 9.16687E-05
A6 -1.46961E-07 -1.04199E-07 9.47152E-09
A8 3.79843E-10 -1.18186E-09 3.67952E-09
A10 -5.81863E-13 0.00000E + 00 0.00000E + 00
A12

[Various data]
INF 200mm
Focal length 14.07 13.46
F number 3.97 3.97
Full angle of view 2ω 90.50 91.83
Statue height Y 14.20 14.20
Total lens length 82.08 82.08

[Variable interval data]
INF 200mm
d0 117.9197
d4 11.9058 7.5487
d6 10.3918 14.7490
BF 18.5984 18.5984

[Lens group data]
Group Start surface Focal length
G1 1 -19.97
G2 5 -104.91
G12 1 -15.16
G3 7 20.48

  FIG. 16 is a lens configuration diagram of the imaging optical system according to Example 4 of the present invention. In order from the object side, the lens unit includes a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 has a negative refractive power as a whole, and the first lens group G1 A negative meniscus lens L1a having a convex surface facing the object side and a negative meniscus lens L1b having a convex surface facing the object side, both lens surfaces of the negative meniscus lens L1a have a predetermined aspherical shape.

  The second lens group G2 has a negative refractive power as a whole, and is composed of a cemented lens composed of two lenses, a positive meniscus lens L2a having a concave surface facing the object side and a biconcave negative lens L2b. ing.

  The third lens group G3 has a positive refractive power as a whole, and includes two lenses, an aperture stop S, a negative meniscus lens L3a having a convex surface facing the object side, and a biconvex positive lens L3b. A cemented lens composed of two lenses, a cemented lens, a flare cut F, a biconvex positive lens L3c, a negative meniscus lens L3d having a convex surface facing the object side, and a biconvex positive lens L3e; A negative meniscus lens L3h including a cemented lens including two lenses, a convex positive lens L3f and a negative meniscus lens L3g having a concave surface facing the object side, and a negative meniscus lens L3h having a concave surface facing the object side. The image-side lens surface has a predetermined aspherical shape.

  The second lens group G2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

Subsequently, specification values of the imaging optical system according to Example 4 are shown below.
Numerical Example 4
Unit: mm
[Surface data]
Surface number rd nd vd
Object ∞ (d0)
1 * 24.4914 2.0000 1.58313 59.46
2 * 10.1923 5.0443
3 20.5045 1.2000 1.49700 81.60
4 11.1542 (d4)
5 -163.0811 1.2922 1.83481 42.72
6 -70.0000 0.8000 1.49700 81.60
7 80.2887 (d7)
8 (Aperture) ∞ 1.1651
9 31.5920 0.8000 1.59282 68.62
10 10.9270 3.4846 1.48749 70.44
11 -31.9827 3.3000
12 (flare cut) ∞ 4.6359
13 23.7463 3.6743 1.43700 95.10
14 -97.6865 2.8555
15 132.4828 0.7500 1.83481 42.72
16 28.9897 4.8214 1.43700 95.10
17 -20.7481 3.6788
18 36.5138 5.5079 1.43700 95.10
19 -15.7784 0.7500 1.88300 40.80
20 -70.9689 2.6458
21 -32.6440 1.1000 1.80610 40.73
22 * -60.9047 (BF)
Image plane ∞

[Aspherical data]
1 side 2 side 22 side
K 0.00000 -1.00000 0.00000
A4 -3.88749E-05 7.20337E-06 3.61522E-05
A6 4.44487E-08 -1.17461E-07 4.09738E-08
A8 -6.25055E-11 -2.24384E-10 3.21264E-10
A10 0.00000E + 00 0.00000E + 00 5.62204E-13
A12

[Various data]
INF 200mm
Focal length 13.97 13.28
F number 3.99 3.99
Full angle of view 2ω 90.89 92.62
Statue height Y 14.20 14.20
Total lens length 89.15 89.15

[Variable interval data]
INF 200mm
d0 110.8529
d4 17.8172 12.9513
d7 4.4872 9.3531
BF 17.3369 17.3369

[Lens group data]
Group Start surface Focal length
G1 1 -18.25
G2 5 -154.10
G12 1 -14.55
G3 7 20.56

  In addition, a list of corresponding values of the conditional expressions in each of these examples is shown.

[Values for conditional expressions]
Conditional expression / Example 1 2 3 4
(1) vdLA> 70.0 81.6 81.6 81.6 81.6
(2) 0.80 <| f12 / f | <1.40 1.08 1.00 1.08 1.04

G1 First lens group G2 Second lens group G3 Third lens group G12 Synthesis of first lens group and second lens group S Aperture stop F Flare cut

Claims (4)

In order from the object side, the first lens group G1 having negative refractive power, the second lens group G2 having negative refractive power, and the third lens group G3 having positive refractive power including the aperture stop S are configured. An imaging optical system satisfying the following conditional expression, wherein the second lens group G2 is moved to the object side along the optical axis during focusing from infinity to a short distance.
(1) vdLA> 70.0
(2) 0.80 <| f12 / f | <1.40
vdLA: Maximum Abbe number of the negative meniscus lens constituting the first lens group G1 with respect to the d-line f12: Combined focal length f1 of the first lens group G1 and the second lens group G2 at infinity Focal length at infinity in the system   The imaging optical system according to claim 1, wherein the second lens group G <b> 2 includes a single lens or a set of units.   3. The imaging optical system according to claim 1, wherein the first lens group G <b> 1 includes only a negative meniscus lens having a convex surface directed toward the object side.   4. The imaging optical system according to claim 1, wherein the first lens group G <b> 1 includes two negative meniscus lenses having a convex surface directed toward the object side. 5.

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