JP2019070705A - Converter optical system and imaging device having the same - Google Patents

Abstract

To obtain a converter optical system that is attached to an object side of a main lens system to change a focal distance of the entire system to a shorter side, and can easily obtain high optical performance.SOLUTION: A converter optical system is arranged at an object side of a main lens system to change a focal distance of the entire system to be shorter than a focal distance of the main lens system. The converter optical system has negative lenses and positive lenses; a lens G1 having a convex surface directed to the object side, having negative refractive power, and having a meniscus shape is arranged at the most object side of the converter optical system; a lens G2 having a concave surface directed to the object side is arranged adjacent to an image side of the lens G1; a radius of a curvature G1R2 of a lens surface at the image side of the lens G1, the radius of the curvature G2R1 of the lens surface at the object side of the lens G2, an average value of an Abbe number νdn of a material of the negative lenses included in the converter optical system, and an average value of the Abbe number νdn of a material of the positive lenses included in the converter optical system are each properly set.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a converter optical system detachably mounted in front (object side) of a main lens system and changing the focal length of the entire system to a shorter one, for example, suitable for imaging mounting such as digital still camera and video camera It is.

  Conventionally, a converter optical system is known that is mounted on the object side of a main lens system that is an imaging optical system and changes the focal length of the entire system to a shorter side (Patent Documents 1 and 2). Patent Documents 1 and 2 disclose a wide converter lens comprising an afocal system mounted on the object side of the main lens system to shift the focal length of the entire system to a shorter one than the focal length of the main lens system.

  Conventionally, in an imaging optical system, the imaging optical system may be used not only in air but also in a solvent having a refractive index of more than 1, such as water. There are known electronic imaging devices that can be favorably performed both in normal imaging in air and in underwater imaging (Patent Documents 3 and 4).

  Patent Document 3 discloses an electronic image pickup unit including an image correction unit that electrically corrects a pickup image obtained by an image pickup element in accordance with a difference between an image pickup under an air environment and an aberration due to an image pickup optical system in an image pickup under an underwater environment. An apparatus is disclosed. Patent Document 4 discloses an imaging apparatus in which an optical system for aberration correction is selectively switched on the image side of an imaging optical system in imaging in air and imaging in water.

JP 2008-026779 A JP, 2009-210692, A JP 2008-236635 A Unexamined-Japanese-Patent No. 2016-200630

  In general, when a converter optical system composed of an afocal system is mounted on the object side of the main lens system, various aberrations increase as a whole system, and the optical performance decreases. In addition, when the area from the object (object) to the lens surface on the most object side of the imaging optical system is immersed in water, the optical state largely changes when the imaging optical system whose optical performance is satisfactorily guaranteed in the air is immersed in water come.

  For example, various aberrations such as lateral chromatic aberration and curvature of field increase when underwater as compared to imaging in air. For this reason, the converter optical system is mounted on the object side of the imaging optical system and images are taken in the air and in water, and the configuration of the converter optical system is appropriately set in order to obtain an image having good optical performance in any of them. Is important.

  It is an object of the present invention to provide a converter optical system which can easily obtain high optical performance by changing the focal length of the entire system to a shorter side by mounting it on the object side of the main lens system, and an imaging apparatus having the same. Do.

The converter optical system according to the present invention is arranged on the object side of the main lens system to change the focal length of the entire system to a direction shorter than the focal length of the main lens system.
The converter optical system has a negative lens and a positive lens, and on the most object side of the converter optical system, a meniscus-shaped lens G1 of negative refractive power, which has a convex surface facing the object side, is disposed. A lens G2 having a concave surface facing the object side is disposed adjacent to the image side of G1.
The curvature radius of the lens surface on the image side of the lens G1 is G1R2, the curvature radius of the lens surface on the object side of the lens G2 is G2R1, and the average value of the Abbe numbers of the materials of negative lenses included in the converter optical system is dndn. When an average value of Abbe numbers of materials of positive lenses included in the converter optical system is dndn,
0.0 <(G2R1 + G1R2) / (G2R1-G1R2) <3.0
dpdp / νdn> 0.9
It is characterized by satisfying the following conditional expression.

  According to the present invention, by mounting the lens system on the object side of the main lens system, it is possible to obtain a converter optical system in which the focal length of the whole system is changed to a shorter one and high optical performance can be easily obtained.

Lens cross section of the converter optical system of Example 1 Lens cross section when the converter optical system of Example 1 is mounted on the object side of the main lens system (A) and (B) longitudinal aberration diagrams at the wide-angle end and the telephoto end when the converter optical system of Example 1 is mounted on the object side of the main lens system Lens cross section of the converter optical system of Example 2 Lens cross section when the converter optical system of Example 2 is mounted on the object side of the main lens system (A) and (B) longitudinal aberration diagrams at the wide-angle end and the telephoto end when the converter optical system of Example 2 is attached to the object side of the main lens system Lens cross section of the converter optical system of Example 3 Lens sectional view when the converter optical system of Example 3 is mounted on the object side of the main lens system (A) and (B) longitudinal aberration diagrams at the wide-angle end and the telephoto end when the converter optical system of Example 3 is mounted on the object side of the main lens system Lens cross section of main lens system used as an example in each embodiment (A) and (B) aberration diagrams at the wide-angle end and at the telephoto end of the main lens system used as an example in each embodiment

  Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. The converter optical system according to the present invention is arranged (mounted) on the object side of the main lens system to change the focal length of the entire system to a direction shorter than the focal length of the main lens system. The converter optical system has a negative lens and a positive lens. A lens G1 having a negative refractive power meniscus shape with a convex surface facing the object side is disposed on the most object side of the converter optical system, and a lens G2 having a concave surface facing the object side adjacent to the image side of the lens G1 Is arranged.

  FIG. 1 is a lens sectional view of a converter optical system according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of a lens when the converter optical system of Embodiment 1 of the present invention is mounted on the object side of the main lens system. FIGS. 3A and 3B are longitudinal aberration diagrams at the wide-angle end and the telephoto end when the converter optical system according to Example 1 of the present invention is attached to the object side of the main lens system and focused at infinity. is there. In Example 1, the focal length of the main lens system is reduced by 0.93 times by mounting the converter optical system.

  FIG. 4 is a lens sectional view of a converter optical system according to a second embodiment of the present invention. FIG. 5 is a cross-sectional view of a lens when the converter optical system of Embodiment 2 of the present invention is mounted on the object side of the main lens system. FIGS. 6A and 6B are longitudinal aberration diagrams at the wide-angle end and the telephoto end when the converter optical system according to the second embodiment of the present invention is attached to the object side of the main lens system and focused at infinity. is there. In Example 2, the focal length of the main lens system is reduced by 0.85 times by mounting the converter optical system.

  FIG. 7 is a lens sectional view of a converter optical system according to a third embodiment of the present invention. FIG. 8 is a lens sectional view when the converter optical system of Embodiment 3 of the present invention is mounted on the object side of the main lens system. FIGS. 9A and 9B are longitudinal aberration diagrams at the wide-angle end and the telephoto end when the converter optical system of Example 3 of the present invention is attached to the object side of the main lens system and focused at infinity. is there. In Example 3, the focal length of the main lens system is reduced by 0.89 times by mounting the converter optical system.

  FIG. 10 is a lens cross-sectional view at the wide-angle end of the main lens system used as an example in each embodiment. FIGS. 11A and 11B are aberration diagrams at the wide-angle end and the telephoto end of the main lens system used as an example in each embodiment.

  Although the main lens system used in each of the embodiments is shown to be a zoom lens, the present invention is not limited to this, and any type of zoom lens may be used, and imaging of a single focal length is also possible. It may be an optical system. In the lens sectional view, WC is a converter optical system. ML is a main lens system. IP is an image plane, and when used as an imaging optical system of a video camera or a digital still camera, an imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives an image is placed. .

  In the spherical aberration diagram, d in the solid line is d-line (wavelength 587.6 nm), g in the two-dot chain line is g-line (wavelength 435.8 nm), and F in the broken line is F-line (wavelength 486.1 nm). In the astigmatism diagram, the dotted line ΔM is a d-line meridional image plane, and the solid line ΔS is a d-line sagittal image plane. The distortion is shown for d-line. Lateral chromatic aberration is represented by g-line. ω is a half angle of view (degrees), and Fno is an F number.

  In each embodiment, the main lens system ML shown in FIG. 10 used as an example is a zoom lens. The main lens system ML includes, in order from the object side to the image side, a first lens unit L1 of negative refractive power, a second lens unit L2 of positive refractive power, and a third lens unit L3 of negative refractive power, The fourth lens unit L4 has a positive refractive power. During zooming from the wide-angle end to the telephoto end, the distance between the first lens unit L1 and the second lens unit L2 is small, and the distance between the second lens unit L2 and the third lens unit L3 is large. Each lens group moves so as to reduce the distance between the fourth lens group L4.

  The main lens system ML shown in FIG. 10 is an example of mounting the converter optical system WC of the present invention, and the main lens system ML to which the converter optical system WC of the present invention is mounted is not limited to this. The main lens system ML may not be a zoom lens, and may be a lens system of any focal length.

  In all of the following embodiments, the main lens system ML to which the converter optical system WC is mounted is common to the main lens system ML in FIG. Longitudinal aberration diagrams at the wide-angle end and the telephoto end when the main lens system ML is photographed in the air are shown in FIGS. 11 (A) and 11 (B).

  When the lens system whose optical performance is guaranteed in the air is put into the water as it is (in a state where water from the subject to the lens surface on the most object side of the lens system is filled with water) Is different. Therefore, the refraction angle at the lens surface (front lens) closest to the object side of the lens system changes, and the optical performance also changes accordingly.

  Specifically, when the off-axis ray is largely refracted by the front lens, the lateral chromatic aberration changes largely from the air. Also, if the front lens has a positive refractive power curvature and the off-axis ray is incident substantially perpendicularly to the front lens, the aberration variation of the magnification color is small, but the field curvature is large from the air It will change. The refractive index of air is about 1.00, and the refractive index of water is about 1.33.

  The converter optical system of the present invention has one or more negative lenses and one or more positive lenses, and mainly corrects the fluctuation of lateral chromatic aberration at the time of underwater photographing. The lens G1 on the most object side of the converter optical system of the present invention has a meniscus shape having a negative refractive power with the convex surface facing the object side. By directing the convex surface to the object side, as described above, the fluctuation of lateral chromatic aberration is reduced. In addition, when photographing in water with the converter optical system attached, the narrowing of the imaging angle of view is reduced as compared with photographing in the air without attaching the converter optical system.

In the converter optical system of the present invention, the curvature radius of the lens surface on the image side of the lens G1 is G1R2, and the curvature radius of the lens surface on the object side of the lens G2 is G2R1. An average value of Abbe numbers of materials of negative lenses included in the converter optical system is dndn, and an average value of Abbe numbers of materials of positive lenses included in the converter optical system is νdn. At this time,
0.0 <(G2R1 + G1R2) / (G2R1-G1R2) <3.0 (1)
dp dp / dn d n> 0.9 (2)
Satisfy the following conditional expression.

  Next, technical meanings of the above-mentioned conditional expressions will be described. Conditional expression (1) defines the shape of the air lens formed between the lens G1 and the lens G2. By satisfying the conditional expression (1), the fluctuation of the curvature of field at the time of shooting in water is corrected. If the upper limit value of the conditional expression (1) is exceeded, it will be difficult to correct the field curvature well. Below the lower limit value, it becomes difficult to miniaturize the converter optical system WC, and if miniaturizing is attempted, the light quantity (peripheral light quantity) near the maximum image height must be reduced, which is preferable. Absent.

Here, the average value of Abbe numbers of materials means Abbe numbers weighted by the refractive power of the lens. For example, there are two positive lenses in the converter optical system WC. One of them has a refractive power of +0.01 and the Abbe number of the material is 40, and the other has a refractive power of +0.02 and the material has an Abbe number of 52. At this time, the average value dpdp of the Abbe number is
dpdp = (40 × 0.01 + 52 × 0.02) / (0.01 + 0.02) = 48
Is calculated.

  Conditional expression (2) is for properly correcting curvature of field at the time of underwater photographing. Generally, if a lens system whose optical performance is guaranteed in air is put into water as it is, curvature of field is over. In order to correct this, it is necessary to increase the Petzval sum in the positive direction, which requires that the material dispersion of the negative lens be equal to or greater than that of the positive lens.

  Therefore, below the lower limit value of the conditional expression (2), it becomes difficult to correct the fluctuation of the curvature of field at the time of photographing in water. As described above, the converter optical system in each embodiment can easily obtain an excellent image quality even in water.

  In particular, the converter optical system of the present invention is mounted on the object side of an imaging optical system in which optical performance is satisfactorily ensured in the air, and even when imaging in water, the change in imaging angle of view is small, and an excellent image An image pickup apparatus can be obtained which can easily be obtained.

  In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions. The effective outer diameter of the lens G1 is D1, and the radius of curvature of the object-side lens surface of the lens G1 is G1R1. The Abbe number of the material of the lens G1 is νdG1. The Abbe number of the material of the positive lens having the largest refractive power among the positive lenses included in the converter optical system is represented by νdPmax.

At this time, it is preferable to satisfy one or more of the following conditional expressions.
D1 / G1 R1> 0.60 (3)
d d G 1 <55.0 (4)
ddPmax> 30.0 (5)

  Next, technical meanings of the above-mentioned conditional expressions will be described. When the value exceeds the upper limit value of the conditional expression (3), it becomes difficult to properly correct magnification chromatic aberration at the time of underwater photographing, and additionally, it becomes difficult to miniaturize the converter optical system. In order to effectively correct lateral chromatic aberration, it is necessary to use a highly dispersed material in a place where the effective diameter is large, that is, the lens G1. When the value exceeds the upper limit value of the conditional expression (4), it becomes difficult to satisfactorily correct lateral chromatic aberration at the time of underwater photographing.

  Generally, when a lens system whose optical performance is guaranteed in air is put into water as it is, lateral chromatic aberration is over. If the lower limit value of the conditional expression (5) is exceeded, the positive lens further causes lateral chromatic aberration to occur on the over side, which makes it more difficult to correct lateral chromatic aberration by the negative lens.

More preferably, the conditional expressions (1) to (5) should satisfy the following numerical range.
0.0 <SF <2.80 (1a)
dpdp / νdn> 1.00 (2a)
D1 / G1R1> 0.61 (3a)
d d G 1 <54.0 (4a)
ddPmax> 40 (5a)

Next, the converter optical system WC of each embodiment will be described.
Example 1
The converter optical system of Example 1 of FIG. 1 will be described. The converter optical system of the first embodiment is composed of three lenses, a negative lens, a negative lens, and a positive lens, arranged in order from the object side to the image side. The converter optical system does not move even when the variable magnification of the main lens system ML (that is, the distance from the first lens surface of the converter optical system WC to the image plane is constant).

  As shown in FIGS. 3A and 3B, longitudinal aberration diagrams at the wide-angle end and the telephoto end in the infinity in-focus condition under water, with the converter optical system of this embodiment mounted on the main lens system ML. As shown in, excellent image quality can be obtained even in water.

Example 2
The converter optical system WC of the second embodiment of FIG. 4 will be described. The converter optical system of the second embodiment includes four lenses, which are disposed in order from the object side to the image side, a negative lens, a negative lens, and a cemented lens in which a negative lens and a positive lens are cemented. The converter optical system WC does not move even when the main lens system ML changes magnification.

  As shown in FIGS. 6A and 6B, the converter optical system WC in the embodiment is mounted on the main lens system ML, and longitudinal aberration diagrams at the wide angle end and the telephoto end in the infinity in-focus condition in water As shown, excellent image quality can be obtained even in water.

[Example 3]
The converter optical system WC of the third embodiment of FIG. 7 will be described. The converter optical system of the third embodiment is composed of three lenses, a negative lens, a negative lens, and a positive lens, arranged in order from the object side to the image side. The converter optical system does not move even when the main lens system ML changes magnification.

  The converter optical system WC in this embodiment is mounted on the main lens system ML, and excellent image quality is obtained in water as shown in longitudinal aberration diagrams at the wide-angle end and the telephoto end in an infinity in-focus condition in water. Be

  As mentioned above, although the preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  Numerical data 1 to 3 corresponding to the main lens system and the first to third examples are shown below. In each numerical data, i represents the order of the surface from the object side, ri is the radius of curvature of the i-th (i-th surface), di is the distance between the i-th surface and the (i + 1) -th surface, ndi and didi are The refractive index and the Abbe number of the material with respect to the d-line are shown. The units of ri and di are both in millimeters. BF is the back focus.

  Each numerical data such as focal length and afocal magnification of the main lens system and the converter optical system is a value in air. In addition, the aspheric surface is indicated by adding a sign of * after the surface number. For the aspheric shape, X is the displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, r is the paraxial radius of curvature, K is the conical constant, A4, A6, When A8, A10, A12 and A14 are aspheric coefficients of each order,

Represented by Note that “E ± XX” in each aspheric coefficient means “× 10 ^{± XX} ”. In addition, numerical values corresponding to the above-mentioned conditional expressions are shown in Table 1.

[Main lens data]
Unit mm
Surface data surface number rd nd d d
1 1. 1.50
2 * -450.407 3.00 1.58313 59.4
3 * 17.067 9.11
4 *-2617.009 2.00 1.88100 40.1
5 * 41.361 6.10
6 -48.208 1.20 1.72916 54.7
7 87.006 0.15
8 46.446 6.50 1.80610 33.3
9-57.922 (variable)
10 33.783 1.00 2.00100 29.1
11 18.908 5.01 1.67300 38.1
12-269.359 6.10
13 (F-stop) ∞ 1.51
14 30.702 1.00 1.84666 23.9
15 20.853 5.67 1.48749 70.2
16 -56.151 (variable)
17 1. 1.72
18 97.298 2.00 1.84666 23.9
19-67.000 0.80 1.88300 40.8
20 28.129 3.00
21 -22.309 0.80 1.91082 35.3
22-60.605 0.15
23 78.956 2.07 1.80809 22.8
24 -86.265 (variable)
25 26.619 6.33 1.49700 81.5
26-82.354 0.15
27 64.520 1.20 1.91082 35.3
28 19.479 10.56 1.49700 81.5
29 -34.761 2.10 1.85400 40.4
30 *-47.490 (variable)
Image plane ∞

Aspheric data second surface
K = 0.00000e + 000 A 4 = 1.69949e-005 A 6 =-2.72616e-008
A 8 = 4.27559e-011 A10 = -4.03114e-014 A12 = 1.89622e-017

Third side
K = -1.45439e + 000 A 4 = 3.81619e-006 A 6 = 2.75066e-008
A 8 = -1.24560e-010 A10 = 5.13319e-014

Fourth side
K = 0.00000e + 000A 4 =-2. 11456e-005 A 6 = 9. 16846e-008
A 8 = -1.71759e-010 A10 = 1.20398e-013

Fifth side
K = -1.28842e + 001 A 4 = 2.71305e-005 A 6 = 3.87882e-008
A 8 = 6.70761e-011 A10 = -2.09035e-014

30th
K = 6.78859e + 000 A 4 = 2.09245e-005 A 6 = 2.40729e-008
A 8 = 1.60019e-010 A10 = -6.04076e-013 A12 = 2.70504e-015

Wide-angle Intermediate telephoto focal length 16.49 23.72 34.14
F number 4.12 4.12 4.19
Half angle of view (degrees) 52.69 42.36 32.36
Image height 21.64 21.64 21.64
Lens total length 156.41 150.15 154.55
BF 39.00 48.72 63.35

d 9 28.15 12.17 1.94
d16 1.41 4.32 7.40
d24 7.12 4.21 1.13
d30 39.00 48.72 63.35

Lens group data group Start focal length
1 1-21.90
2 10 67.08
3 13 53.16
4 17-35.91
5 25 41.87

Single lens data lens Start surface Focal length
1 1 -28.13
2 4 -46.20
3 6-42.38
4 8 32.89
5 10 -44.39
6 11 26.44
7 14 -80.53
8 15 31.96
9 18 47.13
10 19 -22.35
11 21 -39.15
12 23 51.30
13 25 41.27
14 27-31.03
15 28 26.85
16 29 -164.35

[Numeric data 1]
Unit mm
Surface data surface number rd nd dd effective diameter
1 180.000 4.00 1.73641 53.3 126.10
2 97.435 25.00 108.53
3 -226.284 4.00 1.84291 27.8 102.56
4 -2452.736 3.41 97.34
5 92.619 11.98 1.67165 48.6 81.47
6 -1374.309 (variable) 79.30
(Below, main lens)

Afocal magnification 0.93
Wide-angle Mid-telephoto
d 6 5.00 11.26 6.89

Various data
Wide-angle Intermediate telephoto focal length 15.37 22.19 31.45
F number 4.12 4.12 4.12
Half angle of view (degrees) 54.62 44.27 34.53
Image height 21.64 21.64 21.64

Lens group data group Start focal length
1 1 623.29

Single lens data lens Start surface Focal length
1 1 -294.50
2 3-295.98
3 5 129.62

[Numeric data 2]
Unit mm
Surface data surface number rd nd dd effective diameter
1 251.329 4.00 2.00100 29.1 155.33
2 135.065 14.59 138.16
3 291.404 4.00 1.88300 40.8 131.53
4 142.8 37 25.00 120.17
5 83.000 4.00 1.55639 62.7 86.60
6 59.090 17.46 1.57251 42.7 77.93
7 613.441 (variable) 72.74
(Below, main lens)

Afocal magnification 0.85
Wide-angle Mid-telephoto
d 7 5.00 11.27 6.93

Various data
Wide-angle Intermediate telephoto focal length 14.09 20.30 29.05
F number 4.12 4.12 4.16
Half angle of view (degrees) 56.92 46.82 36.68
Image height 21.64 21.64 21.64

Lens group data group Start focal length
1 1 1499.00

Single lens data lens Start surface Focal length
1 1 -296.79
2 3-321.34
3 5 -392.12
4 6 112.92

[Numeric data 3]
Unit mm
Surface data surface number rd nd dd effective diameter
1 110.000 8.00 1.85400 40.4 141.67
2 * 59.244 39.53 102.65
3 800.723 4.00 1.77250 49.6 98.40
4 165.416 2.00 93.66
5 74.857 20.25 1.74616 54.0 89.14
6 -313.147 (variable) 87.00

Aspheric data second surface
K = -1.57744e-001 A 4 = 3.66820e-007 A 6 = 1.22422e-010
A8 = -3.48786e-014 A10 = 1.08255e-016 A12 = -6.19725e-020
A14 = 1.39103e-023

Afocal magnification 0.89
Wide-angle Mid-telephoto
d 6 5.00 11.26 6.89

Various data
Wide-angle Intermediate telephoto focal length 14.68 21.33 29.44
F number 4.12 4.12 4.12
Half angle of view (degrees) 55.84 45.40 36.31
Image height 21.64 21.64 21.64

Lens group data group Start focal length
1 1 217.41

Single lens data lens Start surface Focal length
1 1 -162.12
2 3-270.63
3 5 82.81

ML main lens system WC converter optical system SP aperture stop

Claims (7)

In the converter optical system which is arranged on the object side of the main lens system to change the focal length of the whole system to a direction shorter than the focal length of the main lens system,
The converter optical system has a negative lens and a positive lens, and on the most object side of the converter optical system, a meniscus-shaped lens G1 of negative refractive power, which has a convex surface facing the object side, is disposed. A lens G2 having a concave surface facing the object side is disposed adjacent to the image side of G1.
The curvature radius of the lens surface on the image side of the lens G1 is G1R2, the curvature radius of the lens surface on the object side of the lens G2 is G2R1, and the average value of the Abbe numbers of the materials of negative lenses included in the converter optical system is dndn. When an average value of Abbe numbers of materials of positive lenses included in the converter optical system is dndn,
0.0 <(G2R1 + G1R2) / (G2R1-G1R2) <3.0
dpdp / νdn> 0.9
Converter optical system characterized by satisfying the following conditional expression. Assuming that the effective outer diameter of the lens G1 is D1, and the radius of curvature of the lens surface on the object side of the lens G1 is G1R1,
D1 / G1R1> 0.60
The converter optical system according to claim 1, satisfying the following conditional expression. When the Abbe number of the material of the lens G1 is ddG1,
d d G 1 <55.0
The converter optical system according to claim 1, wherein the conditional expression is satisfied. When the Abbe number of the material of the positive lens having the largest refractive power among the positive lenses included in the converter optical system is ddPmax,
ddPmax> 30.0
The converter optical system according to any one of claims 1 to 3, satisfying the following conditional expression.   The converter optical system according to any one of claims 1 to 4, wherein the converter optical system includes a negative lens, a negative lens, and a positive lens disposed in order from the object side to the image side. .   The converter optical system according to any one of claims 1 to 4, wherein the converter optical system comprises a negative lens, a negative lens, and a cemented lens in which a negative lens and a positive lens are cemented in order from the object side to the image side. Converter optical system according to item 1.   A converter optical system according to any one of claims 1 to 6, a main lens system, and a photoelectric conversion element for receiving an image formed by the converter optical system and the main lens system. Imaging device.