JP2013029658A - Imaging optical system - Google Patents

Abstract

An imaging optical system capable of suppressing a light beam emission angle while realizing an angle of view of 65 degrees or more, enabling quick and quiet focusing, and having a small size and good optical performance.
A first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a negative refractive power are arranged in order from the object side. The lens closest to the object side of the lens unit L1 includes a negative meniscus lens having a convex surface facing the object side. The second lens unit L2 includes a cemented lens L2F including a lens having a negative refractive power and a lens having a positive refractive power. The lens is composed of a lens L2R having a positive refractive power, and moves the second lens unit L2 along the optical axis toward the object side during focusing from infinity to a short distance, and further satisfies a predetermined conditional expression.
[Selection] Figure 1

Description

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

  In recent years, with the widespread use of imaging devices such as digital still cameras and video cameras, the number of pixels of the image sensor has been rapidly increasing, and an image-forming optical system with higher image quality has been demanded. Further, in recent years, an increasing number of cameras employ a large image sensor in order to obtain high image quality.

  If the number of pixels is the same, a large image sensor has a larger area per pixel than a small image sensor, so that a good image with less noise can be obtained.

  In addition, since solid-state imaging devices widely used in imaging devices generally have a characteristic that sensitivity decreases with respect to light having a large incident angle, the imaging optical system has a certain image according to the specifications of the solid-state imaging device. Side telecentricity is required.

  For this reason, in an imaging apparatus that inevitably uses a large solid-state imaging device, the diameter of the entire imaging optical system tends to increase.

  Furthermore, in recent years, it has been required to reduce the weight of the focus lens in order to realize not only a high-speed focusing operation at the time of still image shooting but also an improvement in autofocus followability at the time of moving image shooting.

  Therefore, as an optical system corresponding to a large solid-state image sensor, it is a problem to reduce the weight of the focus lens as much as possible while suppressing the incident angle to the image sensor, that is, the light emission angle from the imaging optical system. Become.

  For example, Patent Documents 1 and 2 disclose an imaging optical system having an angle of view of 60 degrees or more to cope with a large image sensor.

JP 2008-04-0033 A

JP 2011-059288 A

  In the imaging optical system, both miniaturization and performance improvement have been issues, but in the imaging optical system corresponding to a large solid-state imaging device, it is necessary to further suppress the incident angle of the light beam to the imaging device. become.

  The wide-angle lens described in Patent Document 1 adopts a retro-focus type lens configuration and realizes an angle of view of 75 degrees or more, but the incident angle of the maximum field angle principal ray on the image plane exceeds 20 degrees. .

  When this wide-angle lens is used in an image pickup apparatus equipped with a solid-state image pickup device, the sensitivity around the screen gradually decreases with respect to the sensitivity near the screen center. In order to alleviate this phenomenon, it is necessary to set the position of the microlens mounted on the solid-state image pickup device in advance according to the characteristic of the lens to be mounted.

  Therefore, it cannot be said that it is suitable for use in a system with interchangeable lenses that employs a solid-state imaging device.

  On the other hand, the wide-angle lens described in Patent Document 2 has an angle of view of 60 degrees or more, and an incident angle of the maximum field angle principal ray on the image plane is 20 degrees or less.

  Further, the wide-angle lens described in Patent Document 2 has the most object side surface convex toward the object side while the most image side surface is concave toward the image side in the first lens group closer to the object side than the stop, and vice versa. In addition, in the second lens group on the image side of the stop, the most object side surface is concave on the object side, and the most image side surface is convex on the image side.

  In general, by using a concentric lens shape with respect to the stop as described above, it is possible to reduce the incidence angle of off-axis chief rays on each surface and suppress the occurrence of astigmatism and coma on each surface. .

  However, in such an imaging optical system having only the first lens group and the second lens group, the refractive power arrangement changes greatly when the second lens group is moved by focusing, and coma aberration, distortion aberration, and magnification are increased. Variation in chromatic aberration increases.

  Therefore, in the wide-angle lens described in Patent Document 2, the aberration that occurs due to focusing is suppressed by reducing the aberration that occurs in the second lens group. Specifically, in the second lens group, in order from the object side, in addition to the joining (or separation) of the negative lens and the positive lens having a negative composite focal length, the separated positive components are arranged to cancel each other out. By correcting the aberration, the aberration generated due to focusing is corrected.

  However, since these aberrations increase as the angle of view increases, it is difficult to correct and suppress the variation, and it is difficult to further increase the angle of view.

  For example, when the method of Patent Document 2 is applied to a wide-angle lens having an angle of view of 65 degrees or more, the positive refractive power of the second lens group becomes strong in order to ensure the back focus. At this time, in order to suppress the occurrence of astigmatism, coma and the like that increase at the periphery of the screen, an increase in the number of constituent elements of the second lens group cannot be avoided, leading to an increase in the weight of the second lens group. In addition, it is difficult to realize a quick focusing operation.

  The present invention solves the above-mentioned problems, and can reduce the light emission angle while realizing an angle of view of 65 degrees or more, and can perform quick and quiet focusing, and is a compact imaging optical system with good optical performance. The purpose is to provide.

In order to achieve the above object, the imaging optical system embodying the present invention includes, in order from the object side, a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and a negative lens unit. The third lens unit L3 has a refractive power, the most object side lens of the first lens unit L1 is a negative meniscus lens having a convex surface facing the object side, and the second lens unit L2 has a negative refractive power. The lens is composed of a cemented lens L2F composed of a lens and a lens having a positive refractive power, and a lens L2R having a positive refractive power, and moves the second lens unit L2 along the optical axis toward the object side during focusing from infinity to a short distance. The following conditional expression is satisfied.
(1) 0.3 <f1 / f3 <1.0
(2) 0.1 <f2R / f2F <0.7
here,
f1: Focal length of the first lens unit L1 f3: Focal length of the third lens unit L3 f2F: Composite focal length of the cemented lens L2F at the front of the second lens unit f2R: Focal length of the positive lens L2R at the rear of the second lens unit

Furthermore, the imaging optical system for carrying out the present invention satisfies the following conditional expression in the above invention.
(3) 0 <| f2 / r2F | <0.5
here,
r2F: radius of curvature of the most object side surface of the second lens unit L2 f2: focal length of the second lens unit L2

  In the imaging optical system for carrying out the present invention, in the above invention, at least the lens closest to the object side in the first lens unit L1 and the lens closest to the image side in the second lens unit L2 are composed of aspherical surfaces.

  According to the present invention, it is an imaging optical system used for a digital camera, a silver salt camera, a video camera, etc., and the light emission angle is suppressed while realizing an angle of view of 65 degrees or more, and it is suitable for video shooting. In addition, it is possible to provide an imaging optical system that can perform a quiet focus and is small and has good optical performance.

Sectional view of the lens at infinity of the imaging optical system of Example 1 Longitudinal aberration diagram of the imaging optical system of Example 1 at infinity Longitudinal aberration diagram of the imaging optical system of Example 1 at a shooting distance of 400 mm Transverse aberration diagram at infinity of the imaging optical system of Example 1 Lateral aberration diagram of the imaging optical system of Example 1 at a shooting distance of 400 mm Lens cross-sectional view at infinity of the imaging optical system of Example 2 Longitudinal aberration diagram of the imaging optical system of Example 2 at infinity Longitudinal aberration diagram of the imaging optical system of Example 2 at a shooting distance of 400 mm Transverse aberration diagram at infinity of the imaging optical system of Example 2 Lateral aberration diagram of the imaging optical system of Example 2 at a shooting distance of 400 mm Lens cross-sectional view at infinity of the imaging optical system of Example 3 Longitudinal aberration diagram of the imaging optical system of Example 3 at infinity Longitudinal aberration diagram of the imaging optical system of Example 3 at a shooting distance of 400 mm Transverse aberration diagram at infinity of the imaging optical system of Example 3 Lateral aberration diagram of the imaging optical system of Example 3 at a shooting distance of 400 mm Lens cross-sectional view at infinity of the imaging optical system of Example 4 Longitudinal aberration diagram of the imaging optical system of Example 4 at infinity Longitudinal aberration diagram of the imaging optical system of Example 4 at a shooting distance of 400 mm Transverse aberration diagram at infinity of the imaging optical system of Example 4 Lateral aberration diagram of the imaging optical system of Example 4 at a shooting distance of 400 mm Lens cross section at infinity of the imaging optical system of Example 5 Longitudinal aberration diagram of the imaging optical system of Example 5 at infinity Longitudinal aberration diagram of the imaging optical system of Example 5 at a shooting distance of 400 mm Transverse aberration diagram at infinity of the imaging optical system of Example 5 Lateral aberration diagram of the imaging optical system of Example 5 at a shooting distance of 400 mm Lens cross-sectional view at infinity of the imaging optical system of Example 6 Longitudinal aberration diagram of the imaging optical system of Example 6 at infinity Longitudinal aberration diagram of the imaging optical system of Example 6 at a shooting distance of 400 mm Transverse aberration diagram at infinity of the imaging optical system of Example 6 Lateral aberration diagram of the imaging optical system of Example 6 at a shooting distance of 400 mm

  As can be seen from the lens cross-sectional views shown in FIGS. 1, 6, 11, 16, 21, and 26, the imaging optical system of the present invention includes a first lens unit L1 having a negative refractive power and a positive lens unit. The second lens unit L2 having a negative refractive power and the third lens unit L3 having a negative refractive power, and the lens closest to the object side of the first lens unit L1 is configured by a negative meniscus lens having a convex surface facing the object side. The second lens unit L2 includes a cemented lens L2F composed of a negative refracting power lens and a positive refracting power lens and a positive refracting power lens L2R. When focusing from infinity to a short distance, the second lens unit L2 emits light. It is configured to move to the object side along the axis.

The imaging optical system of the present invention having the above configuration satisfies the following conditional expression.
(1) 0.3 <f1 / f3 <1.0
(2) 0.1 <f2R / f2F <0.7
here,
f1: Focal length of the first lens unit L1 f3: Focal length of the third lens unit L3 f2F: Composite focal length of the cemented lens L2F at the front of the second lens unit f2R: Focal length of the positive lens L2R at the rear of the second lens unit

  Conditional expression (1) defines the ratio between the focal length f1 of the first lens unit L1 and the focal length f3 of the third lens unit L3.

  When the lower limit value of conditional expression (1) is exceeded, the focal length of the third lens unit L3 becomes relatively longer and the magnification burden on the third lens unit L3 decreases, but the movement of the second lens unit L2 during focusing is reduced. The amount increases. At this time, the height of the light beam in the second lens unit L2 at the time of focusing on infinity increases, leading to an increase in lens diameter.

  As a result, the weight of the second lens unit L2 increases, and sufficient silence and speed cannot be achieved in the focusing operation.

  When the upper limit value of conditional expression (1) is exceeded, the negative refractive power of the first lens unit L1 is insufficient, and the divergence effect sufficient to realize a wide angle of view of 65 degrees or more with only the first lens unit L1. Cannot be obtained. Therefore, the negative refractive power of the negative lens in the cemented lens L2F in the front part of the second lens unit L2 must be increased.

  On the other hand, since the positive refractive power of the entire second lens unit L2 that is the focus group needs to be maintained, the positive refractive power of the positive lens in the second lens unit L2 is increased, and the curvature radius of each surface is small. As a result, the occurrence of coma becomes particularly large.

  At this time, in order to sufficiently correct aberrations in the second lens unit L2, it is necessary to add a convex component, and an increase in the total lens length and an increase in focus weight are inevitable.

  Conditional expression (2) defines the focal length ratio between the focal length f2F of the cemented lens L2F in the front part of the second lens unit L2 and the focal length f2R of the lens L2R having a positive refractive power in the rear part.

  If the positive refractive power of the cemented lens L2F in the front part of the second lens unit L2 is increased beyond the lower limit value of the conditional expression (2), the spherical aberration that is over in the vicinity of the marginal cannot be corrected.

  When the positive refractive power of the cemented lens L2F in the front part of the second lens unit L2 becomes weaker than the upper limit value of the conditional expression (2), the rear part of the second lens unit L2, which is the focus group, is sufficiently suppressed in order to sufficiently suppress the emission angle. The refractive power burden of the lens L2R having positive refractive power increases. At this time, since the radius of curvature of the positive lens L2R becomes small, the incident angle of off-axis rays becomes tight, and the meridional coma aberration and curvature of field cannot be corrected well.

Further, it is desirable that the imaging optical system of the present invention further satisfies the following conditional expression.
(3) | f2 / r2F | <0.5
here,
r2F: radius of curvature of the most object side surface of the second lens unit L2 f2: focal length of the second lens unit L2

  Conditional expression (3) defines the ratio of the radius of curvature of the most object-side surface of the second lens unit L2 to the focal length of the second lens unit L2.

  When the upper limit value of conditional expression (3) is exceeded, the radius of curvature of the surface closest to the object side of the second lens unit L2 becomes relatively small and a source of sagittal coma aberration is generated, so that a uniform image is obtained up to the periphery of the screen. I can't. Also, the sensitivity to manufacturing errors of the cemented lens L2F at the front of the second lens unit L2 tends to increase.

  In the imaging optical system of the present invention, it is preferable that at least the lens closest to the object side of the first lens unit L1 and the lens closest to the image side of the second lens unit L2 are composed of aspherical surfaces.

  Compared to the case where the lens closest to the object side of the first lens unit L1 is composed of only a spherical surface, an aspherical surface having a shape in which the negative refractive power is weakened as the distance from the optical axis is reduced, thereby reducing distortion. Can do.

  In addition, the most image side lens of the second lens unit L2 has an aspherical surface that has a shape that weakens the positive refractive power as the distance from the optical axis increases, compared to the case where the lens is composed only of a spherical surface. Astigmatism that fluctuates with changes can be effectively suppressed.

  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.

  FIG. 1 is a lens configuration diagram of an imaging optical system according to Example 1 of the present invention.

  The first lens unit L1 includes a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. Has negative refractive power.

  Further, the object side lens surface of the negative meniscus lens closest to the object has a predetermined aspherical shape.

  The second lens unit L2 includes a front lens L2F having a positive refractive power and a rear lens L2R having a positive refractive power, and has a positive refractive power as a whole.

  The front lens L2F is composed of a cemented lens including a biconcave lens and a biconvex lens.

  The rear lens L2R is composed of a biconvex lens.

  The second lens unit L2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, the both lens surfaces of the biconvex lens constituting the rear lens L2R have a predetermined aspherical shape.

  The third lens unit L3 includes a biconcave lens and a biconvex lens, and has a negative refractive power as a whole.

  The image side lens surface of the biconvex lens has a predetermined aspherical shape.

  FIG. 6 is a lens configuration diagram of the imaging optical system according to Example 2 of the present invention.

  The first lens unit L1 includes a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. Has negative refractive power.

  Further, the object side lens surface of the negative meniscus lens closest to the object has a predetermined aspherical shape.

  The second lens unit L2 includes a front lens L2F having a positive refractive power and a rear lens L2R having a positive refractive power, and has a positive refractive power as a whole.

  The front lens L2F is composed of a cemented lens including a biconcave lens and a biconvex lens.

  The rear lens L2R is composed of a biconvex lens.

  The second lens unit L2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

  The image side lens surface of the biconvex lens constituting the rear lens L2R has a predetermined aspherical shape.

  The third lens unit L3 includes a biconcave lens and a biconvex lens, and has a negative refractive power as a whole.

  The image side lens surface of the biconvex lens has a predetermined aspherical shape.

  FIG. 11 is a lens configuration diagram of the imaging optical system according to Example 3 of the present invention.

  The first lens unit L1 includes a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. Has negative refractive power.

  Further, the object side lens surface of the negative meniscus lens closest to the object has a predetermined aspherical shape.

  The second lens unit L2 includes a front lens L2F having a positive refractive power and a rear lens L2R having a positive refractive power, and has a positive refractive power as a whole.

  The front lens L2F is composed of a cemented lens including a biconcave lens and a biconvex lens.

  The rear lens L2R is a positive meniscus lens having a convex surface facing the image side.

  The second lens unit L2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, the image side lens surface of the positive meniscus lens constituting the rear lens L2R has a predetermined aspherical shape.

  The third lens unit L3 includes a cemented lens including a biconcave lens and a biconvex lens, and has a negative refractive power as a whole.

  The image side lens surface of the biconvex lens has a predetermined aspherical shape.

  FIG. 16 is a lens configuration diagram of the imaging optical system according to Example 4 of the present invention.

  The first lens unit L1 includes a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. Has negative refractive power.

  Further, the object side lens surface of the negative meniscus lens closest to the object has a predetermined aspherical shape.

  The second lens unit L2 includes a front lens L2F having a positive refractive power and a rear lens L2R having a positive refractive power, and has a positive refractive power as a whole.

  The front lens L2F is composed of a cemented lens including a biconcave lens and a biconvex lens.

  The rear lens L2R is a positive meniscus lens having a convex surface facing the image side.

  The second lens unit L2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, the image side lens surface of the positive meniscus lens constituting the rear lens L2R has a predetermined aspherical shape.

  The third lens unit L3 includes a cemented lens including a biconcave lens and a biconvex lens, and has a negative refractive power as a whole.

  The image side lens surface of the biconvex lens has a predetermined aspherical shape.

  FIG. 21 is a lens configuration diagram of the imaging optical system according to Example 5 of the present invention.

  The first lens unit L1 includes a negative meniscus lens having a convex surface facing the object side, a cemented lens including a positive meniscus lens having a convex surface facing the object side and a negative meniscus lens having a convex surface facing the object side. And has a negative refractive power as a whole.

  Further, the object side lens surface of the negative meniscus lens closest to the object has a predetermined aspherical shape.

  The second lens unit L2 includes a front lens L2F having a positive refractive power and a rear lens L2R having a positive refractive power, and has a positive refractive power as a whole.

  The front lens L2F is composed of a cemented lens including a biconvex lens and a negative lens.

  The rear lens L2R is composed of a biconvex lens.

  The second lens unit L2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

  The image side lens surface of the biconvex lens constituting the rear lens L2R has a predetermined aspherical shape.

  The third lens unit L3 includes a biconcave lens and a biconvex lens, and has a negative refractive power as a whole.

  The image side lens surface of the biconvex lens has a predetermined aspherical shape.

  FIG. 26 is a lens configuration diagram of the imaging optical system according to Example 6 of the present invention.

  The first lens unit L1 includes a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. Has negative refractive power.

  Further, the object side lens surface of the negative meniscus lens closest to the object has a predetermined aspherical shape.

  The second lens unit L2 includes a front lens L2F having a positive refractive power and a rear lens L2R having a positive refractive power, and has a positive refractive power as a whole.

  The front lens L2F is composed of a cemented lens including a biconcave lens and a biconvex lens.

  The rear lens L2R is a positive meniscus lens having a convex surface facing the image side.

  The second lens unit L2 moves toward the object side along the optical axis during focusing from infinity to a short distance.

  Further, the image side lens surface of the positive meniscus lens constituting the rear lens L2R has a predetermined aspherical shape.

  The third lens unit L3 includes a cemented lens including a biconcave lens and a biconvex lens, and has a negative refractive power as a whole.

  The image side lens surface of the biconvex lens has a predetermined aspherical shape.

  Specific numerical data of each embodiment of the imaging optical system of the present invention described above will be shown below.

  In [Surface Data], the surface number is the number of the lens surface from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, nd is the refractive index with respect to the d-line (wavelength 587.56 nm), vd Indicates the Abbe number with respect to the d-line.

  * (Asterisk) attached to the lens surface number in the first row indicates that the lens surface shape is an aspherical surface. BF represents back focus.

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

  [Various data] shows values of various data when the shooting distance is INF and 400 mm.

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

  In addition, in the values of all the following specifications, the stated focal length f, radius of curvature r, lens surface interval d, and other length units 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.

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

  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. .

Numerical example 1
Unit mm
[Surface data]
Surface number rd nd vd
Surface ∞ Variable
1 * 19.7573 1.2000 1.49710 81.56
2 8.6000 3.9776
3 49.3641 0.9000 1.56732 42.84
4 12.1311 0.8308
5 18.2783 2.9600 1.91082 35.25
6 67.7791 3.6317
7 (Aperture) ∞ Variable
8 -37.4335 0.8500 1.62004 36.30
9 21.1068 3.0265 1.77250 49.62
10 -42.9588 3.4392
11 * 30.4781 5.6963 1.58913 61.25
12 * -12.5222 variable
13 -29.0819 1.0000 1.67270 32.17
14 30.3607 1.7439
15 142.2788 3.9343 1.49710 81.56
16 * -28.0291 22.1998
Image plane ∞

[Aspherical data]
1 side 11 side 12 side 16 side
K 0 0 0 0
A4 4.13638E-05 -4.86522E-06 1.40735E-04 -2.84714E-05
A6 2.24320E-07 5.06408E-08 -1.31253E-07 3.05339E-07
A8 -1.20983E-09 9.55881E-10 3.89495E-09 -8.62682E-10
A10 1.57017E-11 -1.24802E-11 -1.15629E-11 7.76054E-12

[Various data]
INF 400mm
Focal length 18.87 18.82
F number 2.92 2.96
Full angle of view 2ω 75.4-
Statue height Y 14.20 14.20
Total lens length 62.05 62.05
BF 22.20 22.20
Variable distance Object surface ∞ 337.9502
d7 4.6600 4.2317
d12 2.0000 2.4283

[Lens group data]
Group Start surface Focal length
L1 1 -35.13
L2 8 14.23
L3 13 -48.93
L2F 8 109.34
L2R 11 15.84

Numerical example 2
Unit mm
[Surface data]
Surface number rd nd vd
Surface ∞ Variable
1 * 21.1183 1.2000 1.49710 81.56
2 9.2430 3.8078
3 46.4293 0.9366 1.56732 42.84
4 11.6191 0.9239
5 18.1971 2.9513 1.88300 40.81
6 65.3908 3.6805
7 (Aperture) ∞ Variable
8 -67.5244 0.8500 1.62004 36.30
9 18.3801 2.8815 1.80420 46.50
10 -41.0530 5.4428
11 98.9338 4.6404 1.69350 53.20
12 * -14.9091 variable
13 -25.7827 1.0000 1.74077 27.76
14 43.2011 0.2683
15 57.4389 4.9991 1.49710 81.56
16 * -27.8073 21.2552
Image plane ∞ BF

[Aspherical data]
1 surface 12 surfaces 16 surfaces
K 0 0 0
A4 3.77435E-05 6.97896E-05 -2.84475E-06
A6 1.63067E-07 2.84112E-08 8.36964E-08
A8 -1.15802E-09 -1.71949E-10 8.16905E-10
A10 1.11170E-11 5.59165E-12 -2.54347E-12

[Various data]
INF 400mm
Focal length 18.83 18.85
F number 2.90 2.95
Full angle of view 2ω 75.5-
Statue height Y 14.20 14.20
Total lens length 62.00 62.00
BF 21.21 21.21
Variable distance Object surface ∞ 337.9550
d7 4.8470 4.3117
d12 2.3609 2.8962

[Lens group data]
Group Start surface Focal length
L1 1 -34.35
L2 8 15.42
L3 13 -60.10
L2F 8 48.68
L2R 11 19.00

Numerical Example 3
Unit mm
[Surface data]
Surface number rd nd vd
Surface ∞ Variable
1 * 20.3375 1.2000 1.59201 67.02
2 9.5675 3.6415
3 47.1584 0.9000 1.56732 42.84
4 11.9842 0.8645
5 18.0262 3.0436 1.88300 40.81
6 78.7110 3.8505
7 (Aperture) ∞ Variable
8 -73.7004 0.8500 1.62004 36.30
9 20.1793 2.8691 1.80420 46.50
10 -34.6126 5.9919
11 -206.2175 4.2124 1.77010 49.34
12 * -14.9001 Variable
13 -21.9081 1.0000 1.74077 27.76
14 41.8124 4.9031 1.59201 67.02
15 * -29.3003 21.7976
Image plane ∞ BF

[Aspherical data]
1 surface 12 surfaces 15 surfaces
K 0 0 0
A4 3.24297E-05 5.77053E-05 -6.46943E-06
A6 1.31614E-07 4.11225E-08 7.15302E-08
A8 -8.26926E-10 -3.75630E-10 6.91313E-10
A10 8.52452E-12 6.21198E-12 -2.36439E-12

[Various data]
INF 400mm
Focal length 18.87 18.91
F number 2.89 2.95
Full angle of view 2ω 75.3-
Statue height Y 14.20 14.20
Total lens length 62.05 62.00
BF 21.80 21.80
Variable distance Object surface ∞ 337.9550
d9 4.9208 4.3482
d11 2.0000 2.5726

[Lens group data]
Group Start surface Focal length
L1 1 -37.36
L2 8 15.95
L3 13 -68.91
L2F 8 41.56
L2R 11 20.66

Numerical Example 4
Unit mm
[Surface data]
Surface number rd nd vd
Surface ∞ Variable
1 * 20.8128 1.2000 1.59201 67.02
2 9.3513 3.3434
3 37.8156 0.9000 1.56732 42.84
4 11.8615 0.7997
5 17.5225 2.4810 1.88300 40.81
6 70.0319 3.6951
7 (Aperture) ∞ Variable
8 -66.5754 0.8500 1.62004 36.30
9 22.4165 2.7812 1.80420 46.50
10 -37.3785 5.7525
11 -308.2350 4.4533 1.77010 49.34
12 * -14.5018 Variable
13 -22.2890 1.0000 1.74077 27.76
14 40.3119 4.8254 1.59201 67.02
15 * -29.5486 22.2884
Image plane ∞ BF

[Aspherical data]
1 surface 12 surfaces 15 surfaces
K 0 0 0
A4 3.71314E-05 6.03409E-05 -8.21604E-06
A6 1.26369E-07 2.65895E-08 8.43206E-08
A8 -8.81328E-10 -1.24719E-10 6.20932E-10
A10 9.83774E-12 5.67838E-12 -2.28850E-12

[Various data]
INF 400mm
Focal length 18.91 18.95
F number 2.88 2.94
Full angle of view 2ω 75.2-
Statue height Y 14.20 14.20
Total lens length 61.36 61.36
BF 22.29 22.29
Variable distance Object surface ∞ 338.6359
d7 4.9942 4.4220
d12 2.0000 2.5722

[Lens group data]
Group Start surface Focal length
L1 1 -38.05
L2 8 15.85
L3 13 -69.78
L2F 8 48.55
L2R 11 19.63

Numerical Example 5
Unit mm
[Surface data]
Surface number rd nd vd
Surface ∞ Variable
1 * 21.0201 1.2000 1.49710 81.56
2 9.3780 2.6816
3 17.8525 2.7462 1.80610 33.27
4 22.7760 0.9000 1.48749 70.44
5 10.8560 5.9722
6 (Aperture) ∞ Variable
7 31.9831 3.3673 1.74330 49.22
8 -14.5930 0.8500 1.67270 32.17
9 -1233.0946 5.2293
10 72.8681 4.7414 1.69350 53.20
11 * -15.1611 variable
12 -26.9729 1.0000 1.72825 28.32
13 40.6874 2.1150
14 71.7957 3.3632 1.76802 49.24
15 * -52.9713 21.3102
Image plane ∞ BF

[Aspherical data]
1 side 11 side 15 side
K 0 0 0
A4 2.11887E-05 6.46946E-05 6.89202E-06
A6 1.68951E-07 3.77960E-08 1.16321E-07
A8 -1.20889E-09 -1.81822E-10 9.44126E-11
A10 8.38769E-12 5.93463E-12 7.31572E-13

[Various data]
INF 400mm
Focal length 19.02 19.23
F number 2.90 2.93
Full angle of view 2ω 74.9-
Statue height Y 14.20 14.20
Total lens length 62.06 62.06
BF 21.31 21.31
Variable distance Object surface ∞ 337.9400
d6 4.5837 3.9369
d11 2.0000 2.6468

[Lens group data]
Group Start surface Focal length
L1 1 -24.39
L2 7 14.80
L3 12 -61.49
L2F 7 35.24
L2R 10 18.50

Numerical Example 6
Unit mm
[Surface data]
Surface number rd nd vd
Surface ∞ Variable
1 * 19.5000 1.2000 1.59201 67.02
2 11.0885 2.8864
3 52.0564 0.9000 1.56732 42.84
4 11.8091 1.6771
5 19.1964 2.4847 1.88300 40.81
6 117.1759 3.2519
7 (Aperture) ∞ Variable
8 -74.2633 0.8500 1.62004 36.30
9 14.8226 3.2567 1.80420 46.50
10 -37.1078 7.0105
11 -77.6701 3.7904 1.77010 49.34
12 * -15.4494 variable
13 -20.8558 1.0000 1.74077 27.76
14 100.4090 4.0281 1.59201 67.02
15 * -29.9185 21.6403
Image plane ∞ BF

[Aspherical data]
1 surface 12 surfaces 15 surfaces
K 0 0 0
A4 2.20171E-05 5.81230E-05 -7.66673E-06
A6 1.08587E-07 5.09192E-08 6.62491E-08
A8 -8.40134E-10 -1.15351E-10 7.44379E-10
A10 8.57389E-12 7.72799E-12 -3.35374E-12

[Various data]
INF 400mm
Focal length 21.94 21.85
F number 2.92 2.98
Full angle of view 2ω 66.0-
Statue height Y 14.20 14.20
Total lens length 61.35 61.35
BF 21.64 21.64
Variable distance Object surface ∞ 338.6550
d7 5.3691 4.6319
d12 2.0000 2.7372

[Lens group data]
Group Start surface Focal length
L1 1 -60.04
L2 8 17.71
L3 13 -66.73
L2F 8 38.86
L2R 11 24.40

[Values for conditional expressions]
Conditional expression (1) Conditional expression (2) Conditional expression (3)
Formula f1 / f3 f2R / f2F | f2 / r2F |
Range 0.3 <x <1.0 0.10 <x <0.7 x <0.5
Example 1 0.72 0.14 0.38
Example 2 0.57 0.39 0.23
Example 3 0.54 0.50 0.22
Example 4 0.55 0.40 0.24
Example 5 0.40 0.53 0.46
Example 6 0.90 0.63 0.24

L1 First lens group L2 Second lens group L3 Third lens group SP Aperture stop L2F Second lens group front lens L2R Second lens group rear lens

Claims (3)

In order from the object side, the lens unit includes a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and a third lens unit L3 having a negative refractive power.
The most object side lens of the first lens unit L1 is composed of a negative meniscus lens having a convex surface facing the object side,
The second lens unit L2 includes a cemented lens L2F including a lens having a negative refractive power and a lens having a positive refractive power, and a lens L2R having a positive refractive power,
When focusing from infinity to short distance, the second lens unit L2 is moved to the object side along the optical axis,
An imaging optical system satisfying the following conditional expression:
(1) 0.3 <f1 / f3 <1.0
(2) 0.1 <f2R / f2F <0.7
here,
f1: Focal length of the first lens unit L1 f3: Focal length of the third lens unit L3 f2F: Composite focal length of the cemented lens L2F at the front of the second lens unit f2R: Focal length of the positive lens L2R at the rear of the second lens unit The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
(3) 0 <| f2 / r2F | <0.5
here,
r2F: radius of curvature of the most object side surface of the second lens unit L2 f2: focal length of the second lens unit L2   3. The imaging optical system according to claim 1, wherein at least the lens closest to the object side in the first lens unit L <b> 1 and the lens closest to the image side in the second lens unit L <b> 2 are formed of aspherical surfaces. .

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