JP2021167982A - Imaging optical system and imaging device using the same - Google Patents

Abstract

To achieve an imaging optical system that makes an aberration fluctuation small upon focusing from infinity to a near distance, has a high optical performance over an entire focus, and is easy to sufficiently secure peripheral illumination.SOLUTION: In an imaging optical system comprising: a first lens group with positive refractive power; and a second lens group with positive or negative refractive power, in which upon focusing, an interval between the first lens group and the second lens group changes, the first lens group includes an aperture stop. Let a lens highest in an incident height h of an on-axis ray of light on an object side of the aperture stop be a lens Gh, the first lens group consists of: a first a group with negative refractive power that is composed from a lens on a most object side to an adjacent lens on an object side of the lens Gh; a first b group that is composed from the lens Gh to an adjacent lens on the object side of the aperture stop; and a first c group that is composed of a lens arranged on an image side of the aperture stop, in which a focal length f1a of the first a group, and a focal length f of an entire system are each properly set.SELECTED DRAWING: Figure 1

Description

The present invention relates to an imaging optical system, and is particularly suitable for an imaging device such as a single-lens reflex camera, a digital still camera, a film camera, a video camera, or a surveillance camera.

In recent years, the imaging optical system used in an imaging device such as an interchangeable lens still camera is required to have a large aperture ratio, little aberration fluctuation during focusing from infinity to a short distance, and high optical performance over the entire focus range. ing.

Patent Document 1 discloses a wide-angle macro lens system in which sufficient aberration correction is performed even in close-up photography with an imaging magnification of about 1.5. Patent Document 2 discloses a double gauss type macro lens system in which spherical aberration and coma are reduced.

Japanese Unexamined Patent Publication No. 2008-298840 Japanese Unexamined Patent Publication No. 2013-231941

The double-Gauss type imaging optical system is characterized in that it is easy to make a large-diameter ratio and that there is relatively little aberration fluctuation with respect to fluctuations in object distance. However, in a double Gauss type imaging optical system, if the entire system is moved during focusing from infinity to a short distance, the amount of movement of the pupil increases. As a result, when trying to secure the amount of peripheral light over the entire focus range, the effective diameter of the lens increases and the entire system becomes large.

In order to have a large aperture ratio, high optical performance when focusing from infinity to a short distance, and to obtain a sufficient amount of peripheral light, it is important to appropriately set the lens configuration and materials used for each lens. come.

The present invention provides an imaging optical system having little aberration fluctuation due to focusing from infinity to a short distance, having high optical performance over the entire focus range, and easily securing a sufficient amount of peripheral light, and an imaging apparatus having the same. The purpose is.

The imaging optical system of the present invention comprises a first lens group having a positive refractive power and a second lens group having a positive or negative refractive power arranged in order from the object side to the image side. In an imaging optical system in which the distance between the second lens group and the second lens group changes.
When the first lens group includes an aperture aperture and the lens having the highest incident height h of the axial light beam on the object side of the aperture aperture is the lens Gh, the first lens group includes the lens on the object side first. A first group of negative refractive forces composed of up to a lens arranged adjacent to the object side of the lens Gh, from the lens Gh to a lens arranged adjacent to the object side of the aperture aperture. When the group 1b is composed of the group 1c and the group 1c composed of the lenses arranged on the image side of the aperture aperture, the focal distance of the group 1a is f1a, and the focal distance of the entire system is f.
-1.5 <f1a / f <-0.5
It is characterized by satisfying the conditional expression.

According to the present invention, it is possible to obtain an imaging optical system in which aberration fluctuation is small when focusing from infinity to a short distance, high optical performance is obtained over the entire focus range, and it is easy to secure a sufficient amount of peripheral light.

Cross-sectional view of the lens in Example 1 of the present invention (A), (B) Longitudinal aberration diagram at infinity and short distance (photographing magnification 0.5) of Example 1 in the present invention. Cross-sectional view of the lens in Example 2 of the present invention (A), (B) Longitudinal aberration diagram at infinity and short distance (photographing magnification 0.5) of Example 2 in the present invention. Cross-sectional view of the lens in Example 3 of the present invention (A), (B) Longitudinal aberration diagram at infinity and short distance (photographing magnification 0.5) of Example 3 in the present invention. Schematic diagram of the main part of the image pickup apparatus of the present invention

Hereinafter, examples of the imaging optical system of the present invention and an imaging apparatus having the same will be described with reference to the drawings. The imaging optical system of the present invention comprises a first lens group having a positive refractive power and a second lens group having a positive or negative refractive power arranged in order from the object side to the image side. The spacing of the second lens group changes.

FIG. 1 is a cross-sectional view of a lens of the imaging optical system according to the first embodiment of the present invention when it is in focus at infinity. 2 (A) and 2 (B) are longitudinal aberration diagrams of the imaging optical system of the first embodiment of the present invention when they are in focus at infinity and a short distance (imaging magnification −0.5). The first embodiment is an imaging optical system having an F number of 2.91 and an imaging angle of view of 42.2 degrees.

FIG. 3 is a cross-sectional view of the lens of the imaging optical system according to the second embodiment of the present invention when the lens is in focus at infinity. 4 (A) and 4 (B) are longitudinal aberration diagrams of the imaging optical system of the second embodiment of the present invention when they are in focus at infinity and a short distance (imaging magnification −0.5). The second embodiment is an imaging optical system having an F number of 2.91 and an imaging angle of view of 40.8 degrees.

FIG. 5 is a cross-sectional view of the lens of the imaging optical system according to the third embodiment of the present invention when the lens is in focus at infinity. 6 (A) and 6 (B) are longitudinal aberration diagrams of the imaging optical system of the third embodiment of the present invention when they are in focus at infinity and a short distance (imaging magnification −0.5). Example 3 is an imaging optical system having an F number of 2.91 and an imaging angle of view of 41.4 degrees. FIG. 7 is a schematic view of a main part of the image pickup apparatus of the present invention.

The imaging optical system of the present invention is used in imaging devices such as digital cameras, video cameras, broadcasting cameras, surveillance cameras, and silver halide photography cameras.

In the lens cross-sectional views of FIGS. 1, 3, and 5 corresponding to the first to third embodiments, the left side is the object side and the right side is the image side. In the lens cross-sectional view, L0 is an imaging optical system. L1 is a first lens group having a positive refractive power, and L2 is a second lens group having a negative refractive power.

When focusing from infinity to close proximity, the first lens group L1 and the second lens group L2 move toward the object as shown by the arrows so that the distance between them increases. The first lens group L1 is composed of a first group L1a having a negative refractive power, a first group L1b having a positive refractive power, and a first c group L1c having a positive refractive power. The SP is an aperture diaphragm and is arranged in the first lens group L1. The division of each group of the first group L1a, the first b group L1b, and the first c group L1c constituting the first lens group L1 is as follows.

The lens with the highest incident height h of the axial light beam on the object side of the aperture diaphragm SP is referred to as a lens Gh. The first group L1a is composed of a lens closest to the object side to a lens arranged adjacent to the object side of the lens Gh. The first group L1b is composed of a lens Gh to a lens arranged adjacent to the object side of the aperture diaphragm SP. The first c group L1c is composed of lenses arranged on the image side of the aperture diaphragm SP. The IP is an image plane, and when used as an image pickup optical system for a digital still camera or video camera, the image pickup surface of a solid-state image sensor such as a CCD sensor or CMOS sensor corresponds to the film surface for a silver halide film camera. do.

In the aberration diagram, Fno is the F number. ω is the half angle of view (degrees). In the spherical aberration diagram, the solid line d is the d line (wavelength 587.6 nm), and the alternate long and short dash line g is the g line (wavelength 435.8 nm). In the astigmatism diagram, the dotted ΔM is the meridional image plane on the d line, and the solid ΔS is the sagittal image plane on the d line. The distortion diagram shows the d-line. In the chromatic aberration of magnification diagram, g of the alternate long and short dash line is g line. When the numerical data described later is expressed in mm units, the spherical aberration is 0.4 mm, the astigmatism is 0.4 mm, the distortion is 2%, and the chromatic aberration of magnification is 0.05 mm in the longitudinal aberration diagram.

In a double-Gauss type imaging optical system, when a method of moving the entire lens when focusing from infinity to a short distance is adopted, the amount of movement of the pupil due to focusing increases when trying to improve the shooting magnification. As a result, the effective diameter of the lens increases when trying to secure the peripheral illumination over the entire focus range.

In the wide-angle macro lens system disclosed in Patent Document 1, since the negative refractive power of the lens group on the object side is weak, the lens interval is wide and the total length of the lens tends to increase. In the macro lens system disclosed in Patent Document 2, the negative refractive power of the lens group on the object side is weak, and the effective diameter of the lens tends to increase.

In the present invention, by arranging a lens group having a large negative refractive power on the object side, a sufficient amount of peripheral light is secured while having high optical performance when focusing from infinity to a short distance.

The configuration of the imaging optical system of the present invention will be described. The imaging optical system L0 of the present invention includes a first lens group L1 having a positive refractive power and a second lens group L2 having a positive or negative refractive power arranged in order from the object side to the image side. The first lens group L1 has an aperture stop SP. The lens having the highest incident height h of the axial light beam on the object side of the aperture diaphragm SP is referred to as a lens Gh.

At this time, the first lens group L1 is the first a group L1a of negative refractive power composed of the lens closest to the object side to the lens arranged adjacent to the object side of the lens Gh, and the aperture aperture SP from the lens Gh. It has a first group L1b composed of up to a lens arranged adjacent to the object side of the above. Further, it is composed of a first c group L1c composed of lenses arranged on the image side of the aperture diaphragm SP.

Then, when the focal length of the first group L1a is f1a and the focal length of the entire system is f,
-1.5 <f1a / f <-0.5 ... (1)
Satisfies the conditional expression.

Next, the technical meaning of the conditional expression (1) will be described. The conditional expression (1) is a conditional expression for reducing the eclipse of the off-axis luminous flux while preventing the lens from becoming large by appropriately setting the focal length of the first group L1a. When the upper limit of the conditional expression (1) is exceeded and the negative refractive power of the first group L1a becomes stronger (the absolute value of the negative refractive power becomes larger), the bounce of light rays becomes larger and the first group b continues to the image side. The effective diameter of L1b becomes large.

When the lower limit of the conditional equation (1) is exceeded and the negative refractive power of the first group L1a becomes weaker (the absolute value of the negative refractive power becomes smaller), the entrance pupil may be sufficiently moved toward the object. This is not possible, and the diameter of the first group L1a becomes large. More preferably, the numerical range of the conditional expression (1) is set as follows.
-1.0 <f1a / f <-0.6 ... (1a)

As described above, in the present invention, the imaging optical system L0 is obtained, which has less aberration variation during focusing from infinity to a short distance, has high optical performance, and has a sufficient peripheral illumination.

Next, a more preferable configuration of the present invention will be described. Let f1ab be the combined focal length of the first group L1a and the first b group L1b. Let the focal length of the second lens group L2 be f2. Let T1 be the amount of movement of the first lens group L1 on the optical axis when focusing from infinity to a short distance. However, the sign of the amount of movement of the lens group during focusing is positive when the lens group is located on the image side when the lens group is in focus at a short distance as compared with the case where the lens group is in focus at infinity. The short distance means that the imaging magnification is -0.5.

At this time, it is preferable to satisfy one or more of the following conditional expressions.
| F / f1ab | <0.25 ... (2)
| F / f2 | <0.40 ... (3)
0.30 << | T1 / f | <0.95 ... (4)

Next, the technical meaning of each of the above conditional expressions will be described. The conditional expression (2) secures a long back focus by weakening the refractive power of the lens system on the object side of the aperture diaphragm SP, and facilitates compatibility with an imaging device such as a digital single-lens reflex camera. If the upper limit of the conditional expression (2) is exceeded, it becomes difficult to secure a long back focus. The conditional expression (2) is more preferably in the following numerical range.
0.05 << f / f1ab | <0.15 ... (2a)

Conditional expression (3) is for reducing fluctuations in coma aberration and curvature of field during focusing by weakening the refractive power of the second lens group. If the upper limit of the conditional expression (3) is exceeded, it becomes difficult to satisfactorily correct coma aberration and curvature of field. The conditional expression (3) is more preferably in the following numerical range.
| F / f2 | <0.32 ... (3a)

Conditional expression (4) relates to the amount of movement T1 of the first lens group L1 in focusing from infinity to a short distance. If the lower limit of the conditional expression (4) is exceeded, the shooting magnification at a short distance becomes low.

When the upper limit of the conditional expression (4) is exceeded and the amount of movement of the first lens group L1 due to focusing becomes large, the lens barrel holding each lens is likely to have an off-axis luminous flux, or the luminous flux is prevented from being emitted. Therefore, the effective diameter of the lens becomes large. The conditional expression (4) is more preferably in the following numerical range.
0.35 << | T1 / f | <0.85 ... (4a)

Further, in each embodiment, it is preferable to have the following configuration. The lens arranged adjacent to the aperture diaphragm SP included in the first group L1b has a concave lens surface on the image side, and the lens arranged adjacent to the aperture diaphragm SP included in the first c group L1c is an object. It is preferable that the lens surface on the side has a concave shape.

If the lens shape is symmetrical with the aperture diaphragm SP in between, various aberrations, particularly spherical aberration, coma, and the like can be easily corrected. Among the lenses included in the second lens group L2, it is preferable that a positive lens having a concave lens surface on the object side is arranged on the image side most. According to this, when the imaging optical system L0 is used in a digital camera, it becomes easy to reduce ghosts and flares caused by the external light reflected by the sensor surface reflected on the lens surface when taking a picture.

The first group L1a is preferably composed of a negative lens, a positive lens, and a negative lens arranged in order from the object side to the image side. According to this, it becomes easy to satisfactorily correct spherical aberration and coma aberration in the first group L1a.

Next, the features of the lens configuration of each embodiment will be described. In the first embodiment, the first group L1b comprises a positive lens and a bonded lens in which a positive lens and a negative lens are joined, which are arranged in order from the object side to the image side. In Examples 2 and 3, the first group L1b includes a positive lens, a positive lens, and a bonded lens obtained by joining a positive lens and a negative lens, which are arranged in order from the object side to the image side.

In Examples 1 and 2, the first c group L1c is composed of a bonded lens and a positive lens in which a negative lens and a positive lens are joined, which are arranged in order from the object side to the image side. In the third embodiment, the first c group L1c is composed of a bonded lens and a positive lens in which a positive lens and a negative lens are arranged in order from the object side to the image side. In Examples 1 to 3, the second lens group L2 includes negative lenses and positive lenses arranged in order from the object side to the image side.

With the above configuration, it is possible to easily obtain an imaging optical system having high optical performance when focusing from infinity to a short distance and ensuring a sufficient amount of peripheral illumination.

Although examples of the preferred imaging optical system of the present invention have been described above, it goes without saying that the present invention is not limited to these examples, and various modifications and changes can be made within the scope of the gist thereof.

Next, an embodiment of an image pickup apparatus (digital camera) using the image pickup optical system of the present invention will be described with reference to FIG. 7.

In FIG. 7, reference numeral 10 denotes a photographing lens having the imaging optical system 1 of Examples 1 to 3. The imaging optical system 1 is held by a lens barrel 2 which is a holding member. Reference numeral 20 denotes a camera body, which is composed of a quick return mirror 3 that reflects a light beam from the photographing lens 10 upward, and a focal plate 4 arranged at an image forming position of the photographing lens 10. Further, it is composed of a pentadha prism 5 that converts an inverted image formed on the focal plate 4 into an erect image, an eyepiece 6 for observing the erect image, and the like.

Reference numeral 7 denotes a photosensitive surface, on which a solid-state image sensor (photoelectric conversion element) or a silver salt film that receives an image formed by a zoom lens such as a CCD sensor or a CMOS sensor is arranged. At the time of shooting, the quick return mirror 3 retracts from the optical path, and an image is formed on the photosensitive surface 7 by the shooting lens 10. The benefits described in Examples 1 to 3 are effectively enjoyed in the imaging apparatus as disclosed in this Example. Further, the imaging optical system of the present invention can be similarly applied to a mirrorless camera without a quick return mirror. It can also be applied to an image projection optical system for a projector.

Numerical data 1 to 3 corresponding to Examples 1 to 3 are shown below. In each numerical data, i indicates the order of the surfaces counted from the object side. In the numerical data, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air spacing in order from the object side, and ndi and νdi are the i-th lenses in order from the object side. The refractive index and Abbe number of the material.

In addition to specifications such as focal length and F number, the image height is the maximum image height that determines the half angle of view, and the total lens length is the distance from the first lens plane to the image plane. The back focus BF indicates the length from the final lens surface to the image surface. Further, the portion where the distance d of each optical surface is (variable) changes during focusing, and the surface distance when focusing at infinity and a short distance is shown in the attached table. Table 1 shows the relationship between the parameters related to each of the above conditional expressions and the numerical data.

(Numerical data 1)
Unit mm

Surface data Surface number rd nd ν d
1 44.754 1.33 1.51742 52.4
2 20.133 2.64
3 37.890 2.21 1.83481 42.7
4 126.802 1.37
5 -56.860 1.08 1.65412 39.7
6 37.197 0.10
7 25.847 4.24 1.91082 35.3
8-91.901 0.10
9 22.695 5.37 1.49700 81.5
10 -27.281 1.21 1.67300 38.1
11 16.999 4.00
12 (Aperture) ∞ 3.22
13 -17.664 1.08 1.74951 35.3
14 -57.124 2.52 1.77250 49.6
15 -19.984 0.10
16 43.300 3.11 1.59522 67.7
17 -54.253 (variable)
18 -120.283 1.02 1.57135 53.0
19 40.483 1.26
20 -197.824 1.49 1.83400 37.2
21 -47.842 (variable)
Image plane ∞

Various data Infinite focal length 55.99
F number 2.91
Image height 21.60
Lens overall length 83.72

Infinity short distance

d17 1.59 6.52
d21 44.70 64.14

(Numerical data 2)
Unit mm

Surface data Surface number rd nd νd Effective diameter
1 100.713 1.90 1.51742 52.4 34.40
2 31.744 2.40 31.62
3 54.445 3.70 1.83481 42.7 31.45
4 335.375 1.80 31.08
5 -93.936 1.70 1.65412 39.7 31.08
6 65.641 0.15 31.74
7 40.381 5.26 1.91082 35.3 32.72
8 274.681 0.20 32.39
9 97.015 3.61 1.77250 49.6 32.21
10 -230.550 0.15 31.80
11 46.053 6.93 1.43875 94.9 30.02
12 -53.455 1.60 1.67300 38.1 28.55
13 28.307 5.38 25.80
14 (Aperture) ∞ 5.07 25.75
15 -28.710 1.70 1.74951 35.3 25.70
16 -91.895 5.27 1.77250 49.6 27.21
17 -32.073 0.15 28.40
18 59.915 4.50 1.59522 67.7 28.26
19 -138.951 (variable) 27.84
20 -271.305 1.50 1.57135 53.0 27.02
21 59.363 2.14 28.00
22 -463.747 2.49 1.83400 37.2 28.20
23 -84.618 (variable) 28.84
Image plane ∞

Various data Infinite focal length 91.23
F number 2.91
Image height 34.00
Lens overall length 132.54

Infinity short distance
d19 2.62 11.75
d25 72.31 101.74

(Numerical data 3)
Unit mm

Surface data Surface number rd nd νd Effective diameter
1 102.350 1.90 1.51742 52.4 34.74
2 30.964 3.04 31.82
3 54.214 3.61 1.83481 42.7 31.50
4 300.347 1.72 30.99
5 -96.419 1.70 1.65412 39.7 30.99
6 66.963 0.15 31.69
7 39.557 5.68 1.91082 35.3 32.77
8 262.701 0.20 32.37
9 93.505 3.34 1.77250 49.6 32.18
10 -307.363 0.15 31.79
11 45.450 7.06 1.43875 94.9 30.09
12 -53.047 1.60 1.67300 38.1 28.60
13 27.448 2.68 25.82
14 (Aperture) ∞ 5.07 25.84
15 -29.243 4.10 1.77250 49.6 25.87
16 -19.345 1.30 1.74951 35.3 26.63
17 -31.853 0.15 28.00
18 57.017 5.01 1.59522 67.7 27.99
19 -128.825 (variable) 27.52
20 -198.208 1.50 1.57135 53.0 26.32
21 59.707 2.21 27.39
22 -577.406 2.81 1.83400 37.2 27.77
23 -79.829 (variable) 28.54
Image plane ∞

Various data Infinite focal length 90.00
F number 2.91
Image height 34.00
Lens overall length 132.06

Infinity short distance
d19 2.68 10.70
d23 71.55 102.77

L0 Imaging optical system L1 1st lens group L2 2nd lens group L1a 1st group L1b 1b group L1c 1c group SP Aperture aperture

The imaging optical system of the present invention comprises a first lens group having a positive refractive power and a second lens group having a positive or negative refractive power arranged in order from the object side to the image side. In an imaging optical system in which the distance between the second lens group and the second lens group changes.
The first lens group moves during focusing,
The first lens group includes an aperture diaphragm.
When the lens with the highest incident height h of the axial light beam on the object side of the aperture aperture is the lens Gh, the first lens group is arranged adjacent to the object side of the lens Gh from the lens on the most object side. The first group of negative refractive power composed of up to the lens, the first group b composed of the lens Gh to the lens arranged adjacent to the object side of the aperture aperture, on the image side of the aperture aperture. When it is composed of a first c group composed of arranged lenses, and the focal distance of the first group is f1a and the focal distance of the entire system is f,
-1.5 <f1a / f <-0.5
It is characterized by satisfying the conditional expression.

Claims (13)

It consists of a first lens group with a positive refractive power and a second lens group with a positive or negative refractive power arranged in order from the object side to the image side, and the distance between the first lens group and the second lens group during focusing is increased. In a changing imaging optical system
When the first lens group includes an aperture aperture and the lens having the highest incident height h of the axial light beam on the object side of the aperture aperture is the lens Gh, the first lens group includes the lens on the object side first. A first group of negative refractive forces composed of up to a lens arranged adjacent to the object side of the lens Gh, from the lens Gh to a lens arranged adjacent to the object side of the aperture aperture. When the group 1b is composed of the group 1c and the group 1c composed of the lenses arranged on the image side of the aperture aperture, the focal distance of the group 1a is f1a, and the focal distance of the entire system is f.
-1.5 <f1a / f <-0.5
An imaging optical system characterized by satisfying the conditional expression. The lens arranged adjacent to the object side of the aperture diaphragm has a concave lens surface on the image side, and the lens arranged adjacent to the image side of the aperture diaphragm has a concave lens surface on the object side. The imaging optical system according to claim 1, wherein the image pickup optical system is characterized by having a shape. When the combined focal length between the 1st group and the 1b group is f1ab,
| F / f1ab | <0.25
The imaging optical system according to claim 1 or 2, wherein the conditional expression is satisfied. When the focal length of the second lens group is f2,
| F / f2 | <0.40
The imaging optical system according to any one of claims 1 to 3, wherein the conditional expression is satisfied. When the first lens group moves during focusing and the amount of movement of the first lens group due to focusing from infinity to a short distance is T1.
0.30 << | T1 / f | <0.95
The imaging optical system according to any one of claims 1 to 4, wherein the conditional expression is satisfied. The imaging optical system according to any one of claims 1 to 5, wherein a positive lens having a concave lens surface on the object side is arranged on the most image side of the second lens group. The imaging optical system according to any one of claims 1 to 6, wherein the first group 1a comprises a negative lens, a positive lens, and a negative lens arranged in order from the object side to the image side. The first b group according to any one of claims 1 to 7, wherein the first b group comprises a positive lens and a bonded lens in which a positive lens and a negative lens are joined, which are arranged in order from the object side to the image side. Imaging optical system. Any one of claims 1 to 7, wherein the first group 1b comprises a positive lens, a positive lens, and a bonded lens obtained by joining a positive lens and a negative lens, which are arranged in order from the object side to the image side. The imaging optical system according to the above. The first c group according to any one of claims 1 to 9, wherein the first c group comprises a bonded lens in which a negative lens and a positive lens are joined, and a positive lens, which are arranged in order from the object side to the image side. Imaging optical system. The first c group according to any one of claims 1 to 9, wherein the first c group comprises a bonded lens in which a positive lens and a negative lens are joined, and a positive lens arranged in order from the object side to the image side. Imaging optical system. The imaging optical system according to any one of claims 1 to 11, wherein the second lens group comprises a negative lens and a positive lens arranged in order from the object side to the image side. An image pickup apparatus comprising the image pickup optical system according to any one of claims 1 to 12 and an image pickup element that receives an image formed by the image pickup optical system.

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