JP2021105634A - Image formation optical system and imaging apparatus having the same, and imaging system - Google Patents

Abstract

To provide an image formation optical system that has a small-sized focusing mechanism with a small number of lenses and has image-side telecentric properties corresponding to an image pick-up device, an imaging apparatus having the same, and an imaging system.SOLUTION: An image formation optical system is an image formation optical system that is composed of a first lens group having a positive refractive power, a second lens group composed of a negative lens having a negative refractive power and whose surface on an object side is a concave surface, and a third lens group composed of a positive lens having a positive refractive power, which are arranged in order from the object side to an image side. The image formation optical system is composed of five or less lenses, and the third lens group moves in an optical axis direction when focusing is performed.SELECTED DRAWING: Figure 1

Description

The present invention relates to an imaging optical system and is suitable for digital video cameras, digital still cameras, broadcasting cameras, silver halide film cameras, surveillance cameras and the like.

In recent years, there has been a demand for an imaging device capable of telephoto shooting with a small number of lenses, a small size, and an inexpensive configuration. In order to reduce the size of the imaging device, it is important to configure the focusing mechanism to be small. Patent Document 1 discloses a telephoto optical system composed of about five lenses and having a four-group configuration with a second lens group as a junction lens. Further, Patent Document 2 discloses an optical system composed of about five lenses and reducing the weight of the lens group that moves in the focusing group.

Japanese Unexamined Patent Publication No. 2006-64289 Japanese Unexamined Patent Publication No. 2014-137540

The telephoto optical system of Patent Document 1 is configured so that the entire system moves in the optical axis direction during focusing. When such a focusing method of the entire lens extension method is used, the actuator for moving the focus group becomes large, and as a result, the image pickup apparatus becomes large.

In the optical system of Patent Document 2, a so-called rear focus focusing method in which the lens group arranged on the image side is the focus group is used, and a compact focusing mechanism can be configured. However, the angle of view of the optical system of Patent Document 2 is a wide angle and a standard angle of view, and the focus group is composed of a negative lens group. Here, in order to correspond to an image pickup device suitable for a small image pickup device, the optical system is required to have telecentricity on the image side in order to avoid luminance shading and color shading. In the optical system of Patent Document 2, since the negative lens group is arranged on the image side most, it is difficult to secure the telecentric property on the image side. At this time, the main light beam having a peripheral angle of view is obliquely incident on the image plane, so that shading occurs around the screen.

An object of the present invention is to provide an imaging optical system having image-side telecentricity corresponding to an image pickup device, an imaging apparatus having the same, and an imaging system, while providing a compact focusing mechanism with a small number of lenses.

In the imaging optical system as one aspect of the present invention, the imaging optical system has a first lens group having a positive refractive force and a negative refractive force arranged in order from the object side to the image side, and has an object side. It is an imaging optical system composed of a second lens group consisting of a negative lens having a concave surface and a third lens group consisting of a positive lens having a positive refractive force, and the imaging optical system has five or less lenses. It is composed of lenses, and is characterized in that the third lens group moves in the optical axis direction during focusing.

INDUSTRIAL APPLICABILITY The present invention can provide an imaging optical system having image-side telecentricity corresponding to an image pickup element, an imaging apparatus having the same, and an imaging system while having a compact focusing mechanism with a small number of lenses.

It is sectional drawing of the imaging optical system of Example 1. FIG. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 1. It is a longitudinal aberration diagram at the time of focusing at a close distance of Example 1. FIG. It is sectional drawing of the imaging optical system of Example 2. FIG. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 2. It is a longitudinal aberration diagram at the time of focusing at a close distance of Example 2. FIG. It is sectional drawing of the imaging optical system of Example 3. FIG. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 3. It is a longitudinal aberration diagram at the time of focusing at a close distance of Example 3. It is sectional drawing of the imaging optical system of Example 4. FIG. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 4. It is a longitudinal aberration diagram at the time of focusing at a close distance of Example 4. It is the schematic of the image pickup apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same member is given the same reference number, and duplicate description is omitted.

FIGS. 1, 4, 7, and 10 are cross-sectional views of the imaging optical systems of Examples 1 to 4, respectively, at infinity focusing. The imaging optical system of each embodiment is an optical system used in an imaging device such as a digital video camera, a digital still camera, a broadcasting camera, a silver salt film camera, and a surveillance camera.

In each cross-sectional view, the left side is the object side and the right side is the image side. The imaging optical system of each embodiment is configured to have a plurality of lens groups. The lens group may be composed of one lens or may be composed of a plurality of lenses. Further, the lens group may include an aperture diaphragm.

In each cross-sectional view, Li represents the i-th (i = 1, 2, 3) lens group counted from the object side among the lens groups included in the imaging optical system. L2A represents a negative lens having a negative refractive power that constitutes the second lens group, and L3A represents a positive lens having a positive refractive power that constitutes the third lens group.

Further, SP is an aperture stop. GB is an optical block corresponding to an optical filter, a face plate, a low-pass filter, an infrared cut filter, and the like. The IP is an image plane, and an image pickup surface of an image pickup element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is arranged.

Further, the imaging optical system of each embodiment is configured to move the third lens group L3 in the optical axis direction during focusing. The arrows shown in each cross-sectional view indicate the moving direction of the third lens group L3 when focusing from infinity to a close distance.

FIGS. 2, 5, 8 and 11 are longitudinal aberration diagrams of the imaging optical systems of Examples 1 to 4, respectively, at infinity focusing. FIGS. 3, 6, 9 and 12 are longitudinal aberration diagrams when focused at a close distance (2000 mm from the image plane) in Examples 1 to 4, respectively.

In the spherical aberration diagram, Fno is an F number (aperture ratio) and indicates the amount of spherical aberration with respect to the d line (wavelength 587.6 nm) and the g line (wavelength 435.8 nm). In the astigmatism diagram, ΔS indicates the amount of astigmatism on the sagittal image plane, and ΔM indicates the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion with respect to the d line is shown. The chromatic aberration diagram shows the amount of chromatic aberration on the g-line. ω is the imaging half angle of view (°).

Next, a characteristic configuration in the imaging optical system of each embodiment will be described.

The imaging optical system of each embodiment is arranged in order from the object side to the image side, the first lens group L1 having a positive refractive power, the second lens group L2 having a negative refractive power, and the third lens group L2 having a positive refractive power. It is composed of a lens group L3. Further, the imaging optical system is composed of five or less lenses. The second lens group L2 is composed of a negative lens L2A having a negative refractive power and having a concave surface on the object side. The third lens group L3 is composed of a positive lens L3A having a positive refractive power.

In the imaging optical system of each embodiment, since the first lens group L1 has at least one positive lens having a positive refractive power and at least one negative lens having a negative refractive power, axial chromatic aberration can be corrected. be. Further, the surface of the negative lens L2A on the object side is a concave surface. The imaging optical system of the present invention has a function of selectively correcting spherical aberration by having a surface concentric with respect to the aperture SP to minimize the influence on the curvature of field, resulting in good imaging. Performance can be obtained.

In the imaging optical system of the present invention, the third lens group L3 moves in the optical axis direction during focusing. The first lens group L1 and the second lens group L2 are immobile during focusing. By setting the third lens group L3 as the focus group, the actuator for moving the focus group can be miniaturized, so that a compact focusing mechanism can be realized. Further, the weight of the focus group can be reduced by using one positive lens L3A as the focus group.

Further, since the third lens group L3 arranged on the most image side has a positive refractive power, the off-axis main ray is made substantially parallel to the optical axis, and the exit pupil position is moved to the object side to move the high image side. Achieves telecentricity.

By having the above-described configuration, the imaging optical system of each embodiment can have image-side telecentricity corresponding to the image pickup element while having a small number of lenses and a compact focusing mechanism.

The imaging optical system of each embodiment preferably satisfies one or more of the following conditions. Let Bk be the distance from the image side surface of the positive lens L3A at infinity focusing to the image plane IP, and let L be the total length of the imaging optical system. Let f be the focal length of the imaging optical system. Let the focal length of the negative lens L2A, the radius of curvature on the object side, the radius of curvature on the image side, and the Abbe number be f2, r2a, r2b, and ν2, respectively. Let the focal length of the positive lens L3A, the radius of curvature on the object side, the radius of curvature on the image side, and the Abbe number be f3, r3a, r3b, and ν3. Let d23 be the distance from the image-side surface of the negative lens L2A to the object-side surface of the positive lens L3A when focusing at infinity. The lateral magnification of the third lens group L3 is β3.

0.05 <Bk / L <0.30 (1)
-1.00 <f2 / f <-0.15 (2)
0.25 <(r2a + r2b) / (r2b-r2a) <2.50 (3)
0.20 <f3 / f <0.80 (4)
-0.15 <(r3a + r3b) / (r3b-r3a) <1.00 (5)
1.00 <ν2 / ν3 <2.00 (6)
0.05 <d23 / L <0.40 (7)
0.30 <1-β3 ^ 2 <0.90 (8)
The conditional expression (1) relates to the distance of the focus group from the image plane with respect to the total length of the imaging optical system. In general, the accumulation of manufacturing errors causes a back focus shift with respect to the design value. Especially in a telephoto optical system, the back focus shift becomes large, so its correction is important. It is conceivable that the back focus shift is corrected by the focus group, which is a movable group, but if it falls below the lower limit of the conditional expression (1), a sufficient adjustment interval cannot be secured. As a result, it becomes difficult to correct the back focus shift in the ultra-infinite direction, which is not preferable. On the other hand, if the upper limit of the conditional expression (1) is exceeded, the distance between the positive lens L3A and the image plane IP becomes too long. At this time, if the image-side telecentricity is to be maintained, the height of the off-axis marginal ray from the optical axis becomes too large. As a result, the lens diameter of the positive lens L3A becomes large, which is not preferable. By satisfying the conditional expression (1), the imaging optical system can be further miniaturized.

The numerical range of the conditional expression (1) is preferably the range of the following conditional expression (1a).

0.10 <Bk / L <0.25 (1a)
Further, it is more preferable that the numerical range of the conditional expression (1) is the range of the following conditional expression (1b).

0.12 <Bk / L <0.23 (1b)
The conditional expression (2) relates to the refractive power of the second lens group L2. If it is less than the lower limit of the conditional expression (2), the refractive power of the second lens group L2 becomes too weak. Therefore, the spherical aberration is insufficiently corrected. On the other hand, if the upper limit value of the conditional expression (2) is exceeded, the refractive power of the second lens group L2 becomes too strong, and the spherical aberration becomes excessively corrected. Further, in order to secure the image-side telecentricity, it is necessary to strengthen the refractive power of the third lens group L3 more than necessary. At this time, it is not preferable because it becomes difficult to correct the focus fluctuation of the curvature of field in the imaging optical system.

The numerical range of the conditional expression (2) is preferably the range of the following conditional expression (2a).

−0.80 <f2 / f <−0.20 (2a)
Further, it is more preferable that the numerical range of the conditional expression (2) is the range of the following conditional expression (2b).

-0.60 <f2 / f <-0.25 (2b)
Conditional expression (3) relates to the shape of the negative lens L2A. When any of the upper and lower limits of the conditional expression (3) is exceeded, the curvature of the surface of the negative lens L2A on the image side becomes too large. Therefore, it becomes difficult to correct spherical aberration in the imaging optical system, which is not preferable.

The numerical range of the conditional expression (3) is preferably the range of the following conditional expression (3a).

0.50 <(r2a + r2b) / (r2b-r2a) <2.20 (3a)
Further, it is more preferable that the numerical range of the conditional expression (3) is the range of the following conditional expression (3b).

0.80 <(r2a + r2b) / (r2b-r2a) <2.00 (3b)
The conditional expression (4) relates to the refractive power of the third lens group L3. If it falls below the lower limit of the conditional expression (4), the refractive power of the third lens group L3 becomes too strong. Therefore, the aberration fluctuation due to focusing becomes large, which is not preferable. On the other hand, if the upper limit of the conditional expression (4) is exceeded, the refractive power of the third lens group L3 becomes too weak. Therefore, the amount of movement during focusing on a short-distance object increases, which is not preferable.

It is preferable that the numerical range of the conditional expression (4) is the range of the following conditional expression (4a).

0.30 <f3 / f <0.70 (4a)
Further, it is more preferable that the numerical range of the conditional expression (4) is the range of the following conditional expression (4b).

0.35 <f3 / f <0.60 (4b)
Conditional expression (5) relates to the shape of the positive lens L3A. If it is less than the lower limit of the conditional expression (5), the radius of curvature r3b on the image side becomes too small with respect to the radius of curvature r3a on the object side. On the other hand, if the upper limit of the conditional expression (5) is exceeded, the radius of curvature r3b on the image side becomes too large with respect to the radius of curvature r3a on the object side. If any of the upper and lower limits of the conditional expression (5) is exceeded, it becomes difficult to correct the aberration fluctuation due to focusing, which is not preferable.

The numerical range of the conditional expression (5) is preferably the range of the following conditional expression (5a).

-0.05 <(r3a + r3b) / (r3b-r3a) <0.90 (5a)
Further, it is more preferable that the numerical range of the conditional expression (5) is the range of the following conditional expression (5b).

0.05 <(r3a + r3b) / (r3b-r3a) <0.80 (5b)
The conditional expression (6) relates to the dispersion of the lens glass material of the negative lens L2A and the positive lens L3A. If it is less than the lower limit of the conditional expression (6), it becomes difficult to correct the axial chromatic aberration, which is not preferable. On the other hand, if the upper limit of the conditional expression (6) is exceeded, the Abbe number ν3 of the positive lens L3A becomes too small. As a result, the fluctuation of chromatic aberration due to focusing becomes large, which is not preferable.

The numerical range of the conditional expression (6) is preferably the range of the following conditional expression (6a).

1.10 <ν2 / ν3 <1.80 (6a)
Further, it is more preferable that the numerical range of the conditional expression (6) is the range of the following conditional expression (6b).

1.20 <ν2 / ν3 <1.70 (6b)
The conditional expression (7) relates to the distance from the image-side surface of the negative lens L2A to the object-side surface of the positive lens L3A with respect to the overall length of the imaging optical system. If it is less than the lower limit of the conditional expression (7), it is not preferable because a sufficient interval for moving the lens group due to focusing cannot be secured. On the other hand, if the upper limit of the conditional expression (7) is exceeded, it becomes difficult to miniaturize the imaging optical system.

The numerical range of the conditional expression (7) is preferably the range of the following conditional expression (7a).

0.08 <d23 / L <0.35 (7a)
Further, it is more preferable that the numerical range of the conditional expression (7) is the range of the following conditional expression (7b).

0.10 <d23 / L <0.30 (7b)
The conditional expression (8) relates to the focus sensitivity of the third lens group L3. If it is less than the lower limit of the conditional expression (8), the amount of movement during focusing on a short-distance object increases, which is not preferable. On the other hand, if the upper limit of the conditional expression (8) is exceeded, the focus sensitivity becomes too large. As a result, the fluctuation of the focusing object distance becomes too large with respect to the movement amount of the focus group, which makes focusing difficult, which is not preferable.

The numerical range of the conditional expression (8) is preferably the range of the following conditional expression (8a).

0.40 <1-β3 ^ 2 <0.80 (8a)
Further, it is more preferable that the numerical range of the conditional expression (8) is the range of the following conditional expression (8b).

0.50 <1-β3 ^ 2 <0.75 (8b)
Hereinafter, the lens configuration of the imaging optical system of each embodiment will be described. The imaging optical system of each embodiment is arranged in order from the object side to the image side, the first lens group L1 having a positive refractive power, the second lens group L2 having a negative refractive power, and the third lens group L2 having a positive refractive power. It is composed of a lens group L3. The second lens group L2 is composed of a negative lens L2A having a negative refractive power and having a concave surface on the object side. The third lens group L3 is composed of a positive lens L3A having a positive refractive power. Further, the imaging optical system is composed of 4 or more and 5 or less lenses.

In the imaging optical system of the first embodiment, the first lens group L1 is a positive lens having a positive refractive power, a positive lens having a positive refractive power, and a negative negative refractive power arranged in order from the object side to the image side. It is composed of a bonded lens in which the lens is bonded. By using a bonded lens, eccentricity error during manufacturing can be suppressed.

In the imaging optical system of the second embodiment, the first lens group L1 is a positive lens having a positive refractive power, a positive lens having a positive refractive power, and a negative lens having a negative refractive power arranged in order from the object side to the image side. It consists of a lens. By separating the junction lens, the imaging optical system of the second embodiment can secure the degree of freedom of aberration correction as compared with the first embodiment and can easily correct the spherical aberration.

In the imaging optical system of the third embodiment, the first lens group L1 is composed of a positive lens having a positive refractive power and a negative lens having a negative refractive power arranged in order from the object side to the image side. Since the imaging optical system of the third embodiment is a relatively wide-angle optical system as compared with the first embodiment, it is easy to correct chromatic aberration, and the number of lenses in the first lens group L1 can be set to two. can.

In the imaging optical system of the fourth embodiment, the first lens group L1 is a positive lens having a positive refractive power, a negative lens having a negative refractive power, and a positive lens having a positive refractive power arranged in order from the object side to the image side. It is composed of a bonded lens in which the lens is bonded. Since the imaging optical system of the fourth embodiment is a relatively telephoto optical system as compared with the first embodiment, it is difficult to correct the distortion. By making the shape of the negative lens concentric with respect to the aperture SP, it is possible to make the correction of distortion aberration advantageous.

The numerical examples 1 to 4 corresponding to Examples 1 to 4 are shown below. In addition, various values in each numerical example are summarized in Table 1.

In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the mth plane and the (m + 1) th plane. .. However, m is the number of the surface counted from the light incident side. Further, nd represents the refractive index of each optical member with respect to the d line, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is determined when the refractive indexes of the Fraunhofer line d line (587.6 nm), F line (486.1 nm), and C line (656.3 nm) are Nd, NF, and NC.
νd = (Nd-1) / (NF-NC)
It is represented by.

In each numerical example, the axial distance d, the focal length (mm), the F number, and the half angle of view (degrees) are all values when the imaging optical system of each example focuses on an infinity object. Is. BK (back focus) is the distance on the optical axis from the final surface of the lens (the lens surface on the most image side) to the paraxial image plane in terms of air equivalent length. The "total lens length" is the length obtained by adding back focus to the distance on the optical axis from the frontmost surface (lens surface on the most object side) of the imaging optical system to the final surface.
[Numerical Example 1]
Unit mm

Surface data Surface number rd nd ν d
1 7.939 1.49 1.58913 61.1
2 196.316 0.18
3 6.289 1.64 1.48749 70.2
4-381.679 0.46 1.90525 35.0
5 8.050 3.19
6 (Aperture) ∞ 4.82
7 -3.531 0.46 1.51633 64.1
8 391.895 (variable)
9 11.436 1.66 1.70154 41.2
10 -17.755 (variable)
11 ∞ 0.92 1.51633 64.1
12 ∞ 0.74
Image plane ∞

Focal length 25.98
F number 4.00
Half angle of view (degrees) 6.59
Image height 3.00
Lens overall length 20.78
BK 3.19

Lens group data group Start surface focal length
1 1 16.64
2 7 -6.78
3 9 10.15

focus
Infinity 2000mm
d8 3.36 2.84
d10 1.84 2.36

[Numerical Example 2]
Unit mm

Surface data Surface number rd nd ν d
1 8.928 1.97 1.83481 42.7
2 51.503 0.14
3 6.780 1.60 1.53775 74.7
4 16.163 0.46
5 46.287 0.46 1.80518 25.4
6 5.412 4.08
7 (Aperture) ∞ 4.82
8-4.716 0.46 1.48749 70.2
9 -15.099 (variable)
10 17.259 2.07 1.86300 41.5
11 -19.355 (variable)
12 ∞ 0.92 1.51633 64.1
13 ∞ 1.62
Image plane ∞

Focal length 25.98
F number 2.80
Half angle of view (degrees) 6.59
Image height 3.00
Lens overall length 23.93
BK 4.07

Lens group data group Start surface focal length
1 1 24.14
2 8 -14.27
3 10 10.86

focus
Infinity 2000mm
d9 3.49 3.02
d11 1.84 2.32

[Numerical Example 3]
Unit mm

Surface data Surface number rd nd ν d
1 4.835 1.41 1.86300 41.5
2 -21.401 0.20
3 -14.436 0.46 1.84666 23.8
4 8.515 0.36
5 (Aperture) ∞ 4.82
6 -2.552 0.46 1.56732 42.8
7 -8.151 (variable)
8 12.183 1.53 1.86300 41.5
9 -15.239 (variable)
10 ∞ 0.92 1.51633 64.1
11 ∞ 0.74
Image plane ∞

Focal length 14.72
F number 4.00
Half angle of view (degrees) 11.52
Image height 3.00
Lens overall length 14.41
BK 3.19

Lens group data group Start surface focal length
1 1 11.43
2 6 -6.75
3 8 8.05

focus
Infinity 2000mm
d7 1.66 1.51
d9 1.84 1.99

[Numerical Example 4]
Unit mm

Surface data Surface number rd nd ν d
1 14.742 1.00 1.49700 81.5
2 46.865 0.28
3 9.695 0.46 1.84666 23.8
4 6.839 1.38 1.78800 47.4
5 12.873 7.48
6 (Aperture) ∞ 4.82
7 -5.416 0.46 1.48749 70.2
8 106.273 (variable)
9 11.225 1.38 1.71300 53.9
10 -92.287 (variable)
11 ∞ 0.92 1.51633 64.1
12 ∞ 1.38
Image plane ∞

Focal length 34.51
F number 4.00
Half angle of view (degrees) 4.97
Image height 3.00
Lens overall length 28.99
BK 3.82

Lens group data group Start surface focal length
1 1 21.28
2 7 -10.56
3 9 14.11

focus
Infinity 2000mm
d8 7.60 6.62
d10 1.84 2.83

[Imaging device]
An example of a digital still camera (imaging apparatus) using the imaging optical system of the present invention as a photographing optical system will be described with reference to FIG. In FIG. 13, 10 is a camera body, and 11 is a photographing optical system configured by any of the imaging optical systems described in Examples 1 to 4. Reference numeral 12 denotes an image pickup element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor, which is built in the camera body and receives an optical image formed by the photographing optical system 11 and performs photoelectric conversion. The camera body 10 may be a so-called single-lens reflex camera having a quick turn mirror, or a so-called mirrorless camera having no quick turn mirror.

By applying the imaging optical system of the present invention to an imaging device such as a digital still camera in this way, it is possible to obtain an imaging device having a small lens.
[Imaging system]
An imaging system (surveillance camera system) including the imaging optical system of each embodiment and a control unit that controls the imaging optical system may be configured. In this case, the control unit can control the imaging optical system so that the third lens group L3 moves as described above during focusing. At this time, the control unit does not have to be integrally configured with the imaging optical system, and the control unit may be configured as a separate body from the imaging optical system. For example, a control unit (control device) arranged far from the drive unit that drives each lens of the imaging optical system includes a transmission unit that sends a control signal (command) for controlling the imaging optical system. The configuration may be adopted. According to such a control unit, the imaging optical system can be remotely controlled.

Further, by providing an operation unit such as a controller or a button for remotely controlling the imaging optical system in the control unit, the imaging optical system may be controlled in response to an input to the user's operation unit. ..

Further, the imaging system may have a display unit such as a liquid crystal panel that displays information (moving state of the focus group) regarding the focusing position of the imaging optical system. The information regarding the focusing position of the imaging optical system is, for example, the subject distance. In this case, the user can remotely control the imaging optical system via the operating unit while viewing the information on the focusing position of the imaging optical system shown on the display unit. At this time, the display unit and the operation unit may be integrated by adopting, for example, a touch panel.

Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications and modifications can be made within the scope of the gist thereof.

L1 1st lens group L2 2nd lens group L3 3rd lens group L2A Negative lens L3A Positive lens

Claims (18)

A first lens group having a positive refractive power, a second lens group consisting of a negative lens having a negative refractive power and a concave surface on the object side, arranged in order from the object side to the image side, a positive refractive power It is an imaging optical system composed of a third lens group consisting of positive lenses of the above.
The imaging optical system consists of five or less lenses.
An imaging optical system characterized in that the third lens group moves in the optical axis direction during focusing. When the distance from the image side surface of the positive lens to the image surface at infinity is Bk and the total length of the imaging optical system is L,
0.05 <Bk / L <0.30
The imaging optical system according to claim 1, wherein the conditional expression is satisfied. When the focal length of the imaging optical system is f and the focal length of the negative lens is f2,
-1.00 <f2 / f <-0.15
The imaging optical system according to claim 1 or 2, wherein the conditional expression is satisfied. When the radius of curvature of the negative lens on the object side is r2a and the radius of curvature of the negative lens on the image side is r2b, 0.25 <(r2a + r2b) / (r2b-r2a) <2.50
The imaging optical system according to any one of claims 1 to 3, wherein the conditional expression is satisfied. When the focal length of the imaging optical system is f and the focal length of the positive lens is f3,
0.20 <f3 / f <0.80
The imaging optical system according to any one of claims 1 to 4, wherein the conditional expression is satisfied. When the radius of curvature of the positive lens on the object side is r3a and the radius of curvature of the positive lens on the image side is r3b,
-0.15 <(r3a + r3b) / (r3b-r3a) <1.00
The imaging optical system according to any one of claims 1 to 5, wherein the conditional expression is satisfied. When the Abbe number of the negative lens is ν2 and the Abbe number of the positive lens is ν3,
1.00 <ν2 / ν3 <2.00
The imaging optical system according to any one of claims 1 to 6, wherein the conditional expression is satisfied. When the distance from the image-side surface of the negative lens to the object-side surface of the positive lens at infinity is d23, and the total length of the imaging optical system is L,
0.05 <d23 / L <0.40
The imaging optical system according to any one of claims 1 to 7, wherein the conditional expression is satisfied. When the lateral magnification of the positive lens at infinity is β3,
0.30 <1-β3 ^ 2 <0.90
The imaging optical system according to any one of claims 1 to 8, wherein the conditional expression is satisfied. The first lens group is characterized by comprising a positive lens having a positive refractive power, a positive lens having a positive refractive power, and a negative lens having a negative refractive power arranged in order from the object side to the image side. The imaging optical system according to any one of 1 and 9. The first lens group is any one of claims 1 and 9, wherein the first lens group comprises a positive lens having a positive refractive power and a negative lens having a negative refractive power arranged in order from the object side to the image side. The imaging optical system according to. The first lens group is characterized by comprising a positive lens having a positive refractive power, a negative lens having a negative refractive power, and a positive lens having a positive refractive power arranged in order from the object side to the image side. The imaging optical system according to any one of 1 and 9. The imaging optical system according to any one of claims 1 to 12, wherein the imaging optical system includes four or more lenses. The imaging optical system according to any one of claims 1 to 13.
An image pickup apparatus including an image pickup element that receives an image formed by the imaging optical system. An imaging system comprising the imaging optical system according to any one of claims 1 to 14 and a control unit that controls the imaging optical system. The fifteenth aspect of the present invention, wherein the control unit is configured as a separate body from the imaging optical system, and has a transmitting unit that transmits a control signal for controlling the imaging optical system. Imaging system. The imaging system according to claim 15 or 16, wherein the control unit is configured as a separate body from the imaging optical system, and includes an operating unit for operating the imaging optical system. The imaging system according to any one of claims 15 to 17, further comprising a display unit that displays information regarding the focusing position of the imaging optical system.

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