JP2020201295A - Converter lens, interchangeable lens, and imaging apparatus - Google Patents

Abstract

To provide a small size converter lens having a high optical performance when placed at the image side of a master lens.SOLUTION: A converter lens RCL having a negative refractive power makes the focal length of the entire system longer than the focal length of the master lens ML alone when placed at the image side of the master lens ML. The refractive index Nd on the d line and the Abbe number νd based on the d line of the negative lens material of the converter lens RCL satisfies the following conditions: 2.20<Nd<2.37, 13.00<νd<23.00.SELECTED DRAWING: Figure 1

Description

The present invention relates to a converter lens, an interchangeable lens, and an imaging device.

A rear converter lens is known that can extend the focal length of the entire system by being arranged between an image pickup device and an interchangeable lens including a master lens. Since such a rear converter lens has a negative refractive power, the Petzval sum of the rear converter lens tends to increase in the negative direction. Therefore, the curvature of field tends to increase when the master lens is arranged on the image side. In addition, since the aperture diaphragm is not arranged in the rear converter lens and the aperture diaphragm included in the master lens is often used instead, the main ray of the off-axis light beam does not intersect the optical axis in the rear converter lens. It passes through a position radially away from the optical axis. As a result, the curvature of field tends to be large, and it tends to be difficult to correct aberrations such as chromatic aberration of magnification caused by the off-axis luminous flux.

Patent Document 1 describes a rear converter lens using a material having a high partial dispersion ratio in a negative lens.

Japanese Unexamined Patent Publication No. 2011-123336

In order to obtain high optical performance in the rear converter lens, it is important to more appropriately determine the refractive index, Abbe number, etc. of the material of the negative lens.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a converter lens having high optical performance when arranged on the image side of a master lens.

The converter lens according to an embodiment of the present invention has a negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone. It ’s a lens
When the refractive index of the material on the d line is Nd and the Abbe number based on the d line is νd,
2.20 <Nd <2.37
13.00 <νd <23.00
It is characterized by having a negative lens satisfying the conditional expression.

According to the present invention, it is possible to obtain a converter lens having high optical performance when it is arranged on the image side of the master lens.

It is sectional drawing of a master lens and a converter lens. It is sectional drawing of the converter lens of Example 1. FIG. It is an aberration diagram at the time of focusing on an infinity object when the converter lens of Example 1 is arranged on the image side of a master lens. It is sectional drawing of the converter lens of Example 2. FIG. It is an aberration diagram at the time of focusing on an infinity object when the converter lens of Example 2 is arranged on the image side of a master lens. It is sectional drawing of the converter lens of Example 3. FIG. It is an aberration diagram at the time of focusing on an infinity object when the converter lens of Example 3 is arranged on the image side of a master lens. It is a figure which shows the structure of the image pickup apparatus.

Hereinafter, the rear converter lens (hereinafter referred to as a converter lens) and the imaging device according to the embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the converter lens RCL of the embodiment of the present invention is arranged on the image side of a master lens ML (main lens system) such as an interchangeable lens. As a result, the focal length of the photographing optical system (entire system) including the master lens ML and the converter lens RCL is made longer than when only the master lens ML is used as the photographing optical system.

The master lens ML is a photographing lens system used in an imaging device such as a digital video camera, a digital camera, a silver salt film camera, and a TV camera.

In the cross-sectional view of the master lens ML shown in FIG. 1 and the cross-sectional view of the converter lens RCL shown in FIGS. 2, 4, and 6, the left side is the object side (front) and the right side is the image side (rear). The aperture stop SP determines (limits) the luminous flux of the open F number (Fno). At the mounting position MNT, the lens barrel containing the converter lens RCL is mounted on the lens barrel containing the master lens ML.

When the image pickup device is a digital video camera, a digital camera, or the like, the image plane IP corresponds to the image pickup surface of an image pickup element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor. When the image pickup device is a silver halide film camera, the image plane IP corresponds to the film plane.

FIGS. 3, 5 and 7 are aberration diagrams of the converter lens RCL of each embodiment described later. In the spherical aberration diagram, the solid line shows the d line and the alternate long and short dash line shows the g line. In the astigmatism diagram, the broken line M indicates the amount of aberration in the meridional image plane, and the solid line S indicates the amount of aberration in the sagittal image plane. Distortion is shown for line d. Chromatic aberration of magnification is shown for the g-line. ω is the half angle of view (degrees). Fno is an F number.

The converter lens RCL according to the embodiment has a negative refractive power, and by being arranged on the image side of the master lens, the focal length of the entire system is made longer than the focal length of the master lens alone.

The converter lens RCL has a negative lens Ln made of a material having a relatively high refractive index and a high partial dispersion. Specifically, when the refractive index of the negative lens Ln on the d line (587.56 nm) is Nd and the Abbe number based on the d line is νd, the following conditional expressions (1) and (2) are satisfied.
2.20 <Nd <2.37 ... (1)
13.00 <νd <23.00 ... (2)

However, the Abbe number νd is when the refractive indexes of the d-line, F-line (486.13 nm), and C-line (656.27 nm) are Nd, NF, and NC, respectively.
νd = (Nd-1) / (NF-NC)
It is expressed as.

Conditional expression (1) relates to the refractive index of the material of the negative lens Ln, and by satisfying this conditional expression, curvature of field can be satisfactorily corrected. If it is less than the lower limit of the conditional expression (1), the Petzval sum becomes large in the negative direction (the absolute value of the Petzval sum becomes large), and the curvature of field deteriorates, which is not preferable. It is difficult to produce a material having a refractive index exceeding the upper limit of the conditional expression (1), and even if it can be produced, it is difficult to mass-produce it, which is not preferable.

Conditional expression (2) relates to the Abbe number of the material of the negative lens Ln, and by satisfying this conditional expression, axial chromatic aberration and chromatic aberration of magnification can be satisfactorily corrected. In the following description, when axial chromatic aberration and chromatic aberration of magnification are not particularly distinguished, they are simply referred to as "chromatic aberration". If the Abbe number is smaller than the lower limit of the conditional expression (2), chromatic aberration will be overcorrected, which is not preferable. If it exceeds the upper limit of the conditional expression (2), the chromatic aberration will be insufficiently corrected, which is not preferable.

As described above, by having the negative lens Ln satisfying the conditional equations (1) and (2), the converter lens RCL can have high optical performance when arranged on the image side of the master lens ML.

It is preferable that the numerical range of the conditional expressions (1) and (2) is as follows.
2.22 <Nd <2.35 ... (1a)
15.00 <νd <22.00 ... (2a)

It is more preferable that the numerical range of the conditional expressions (1) and (2) is as follows.
2.23 <Nd <2.34 ... (1b)
16.00 <νd <21.00 ... (2b)

It is possible to correct curvature of field by using a material having a high partial dispersion ratio for the negative lens as in Patent Document 1 described above. However, in the rear converter lens of Patent Document 1, it is important to appropriately set the partial dispersion ratio of the material of the negative lens in order to correct the axial chromatic aberration and the chromatic aberration of magnification in a more balanced manner.

Therefore, in the converter lens RCL, it is preferable to satisfy the conditional expression (3) with respect to the partial dispersion ratio θgF of the material of the negative lens Ln.
0.017 <θgF-0.6438 + 0.001682 × νd <0.040
... (3)

Here, θgF has the refractive indexes of the material of the negative lens Ln at the F line (486.13 nm), the C line (656.27 nm), and the g line (435.84 nm) as NF, NC, and Ng.
θgF = (Ng-NF) / (NF-NC)
It is expressed as.

The conditional expression (3) can satisfactorily correct the secondary spectrum with respect to the partial dispersion ratio of the negative lens Ln, and can correct the axial chromatic aberration and the chromatic aberration of magnification in a well-balanced manner. If it is less than the lower limit of the conditional expression (3), the anomalous dispersibility of the negative lens Ln becomes too small, and the correction of chromatic aberration of magnification is insufficient, which is not preferable. If it exceeds the upper limit of the conditional expression (3), the anomalous dispersibility of the negative lens Ln becomes too large, and the axial chromatic aberration becomes overcorrected, which is not preferable.

Further, since the partial dispersion ratio is appropriately set and the chromatic aberration can be easily corrected, the refractive power of the entire system of the converter lens RCL can be easily strengthened. This is advantageous for miniaturization of the converter lens RCL.

Further, it is preferable that the converter lens RCL satisfies one or more of the following conditional expressions (4) to (7).
0.25 <fn / f <1.00 ... (4)
1.80 <Nd_ave <2.00 ... (5)

0.50 <Dn / TL <0.98 ... (7)

Let f be the focal length of the converter lens RCL and fn be the focal length of the negative lens Ln. Let Nd_ave be the average refractive index of all the negative lens materials contained in the converter lens RCL in the d-line. When the converter lens RCL consists of N lenses, the focal length of the i-th (i = 1-N) lens of the converter lens RCL counting from the object side is fi, and the i-th (i = 1) lens counting from the object side. Let νdi be the Abbe number based on the d-line of the lens of ~ N). The distance on the optical axis from the most object-side surface of the converter lens RCL to the most image-side surface is TL, and the distance on the optical axis from the most object-side surface of the converter lens RCL to the object-side surface of the negative lens Ln. Let be Dn.

The conditional expression (4) defines the focal length of the negative lens Ln and the focal length of the converter lens RCL, and by satisfying this conditional expression, both high optical performance and miniaturization of the entire system can be achieved. .. If the focal length of the negative lens Ln becomes shorter and the refractive power becomes stronger below the lower limit of the conditional expression (4), it becomes difficult to satisfactorily correct the chromatic aberration of magnification, which is not preferable. If the upper limit of the conditional expression (4) is exceeded and the focal length of the negative lens Ln becomes long and the refractive power becomes weak, the converter lens RCL becomes large, which is not preferable.

Conditional equation (5) can correct curvature of field and chromatic aberration in a well-balanced manner by satisfying the conditional equation with respect to the refractive indexes of all the negative lens materials contained in the converter lens RCL. When the value falls below the lower limit of the conditional expression (5), the refractive index of each negative lens in the converter lens RCL becomes smaller and the Petzval sum becomes larger in the negative direction (the absolute value of the Petzval sum becomes larger), and the curvature of field becomes larger. Is not preferable because it worsens. If the upper limit of the conditional expression (5) is exceeded, the material options are greatly limited. This makes it difficult to correct axial chromatic aberration and chromatic aberration of magnification in a well-balanced manner, which is not preferable.

The conditional expression (6) defines the sum of the products of the focal length of each lens and the Abbe number of the material, and the chromatic aberration can be further corrected by satisfying the conditional expression (6). If it exceeds the upper limit of the conditional expression (6), it becomes difficult to correct the chromatic aberration, which is not preferable.

Conditional expression (7) relates to the position of the negative lens Ln, and by satisfying this conditional expression, axial chromatic aberration and chromatic aberration of magnification can be corrected in a well-balanced manner. If the negative lens Ln is arranged on the object side below the lower limit of the conditional expression (7), the axial chromatic aberration will be overcorrected and the chromatic aberration of magnification will be insufficiently corrected, which is not preferable. It is physically difficult to arrange the negative lens Ln on the image side beyond the upper limit of the conditional expression (7).

It is preferable that the numerical range of the conditional expressions (3) to (7) is as follows.
0.020 <θgF-0.6438 + 0.001682 × νd <0.038
... (3a)
0.27 <fn / f <0.85 ... (4a)
1.83 <Nd_ave <1.97 ... (5a)

0.52 <Dn / TL <0.96 ... (7a)

It is more preferable that the numerical range of the conditional expressions (3) to (11) is as follows.
0.022 <θgF-0.6438 + 0.001682 × νd <0.036
... (3b)
0.28 <fn / f <0.75 ... (4b)
1.85 <Nd_ave <1.95 ... (5b)

0.54 <Dn / TL <0.95 ... (7b)

By satisfying at least one of the above conditional expressions, high optical performance can be obtained by satisfactorily correcting various aberrations such as curvature of field and chromatic aberration while making the converter lens RCL compact.

Next, a preferable configuration of the converter lens RCL will be described.

The converter lens RCL preferably has a bonded lens La composed of a positive lens and a negative lens, which is arranged closest to the object side. By arranging the junction lens La at a position where the peripheral light of the axial luminous flux is high, the axial chromatic aberration can be satisfactorily corrected.

Further, it is preferable that the converter lens RCL is composed of a plurality of positive lenses and a plurality of negative lenses, and these positive lenses and negative lenses are alternately arranged on the optical axis. As a result, the luminous flux can be converged from the object side to the image side while correcting the axial chromatic aberration and the Magnification chromatic aberration.

The converter lens RCL preferably has a lens element Lp having a positive refractive power, which is arranged on the image side most. As a result, the curvature of field can be corrected by arranging the lens element Lp at a position where the main ray of the off-axis luminous flux is high. The lens element arranged on the most image side means a lens arranged on the most image side or a bonded lens including the lens when the lens is a part of the bonded lens.

Next, the master lens ML of the embodiment and the converter lens RCL of the embodiment will be described.

[Master lens]
In the present specification, the configuration of the master lens ML is common to Examples 1 to 3 of the converter lens RCL.

FIG. 1 is a cross-sectional view of the master lens ML when focusing on an infinite object. The master lens ML has an F number of 2.90, a half angle of view of 3.16 degrees, and a back focus of 44 mm. The configuration of the master lens ML given in the examples is an example, and other optical systems may be used as long as they can form an image on the image plane IP.

[Converter lens]
Next, the converter lens RCL of Examples 1 to 3 will be described.

[Example 1]
FIG. 2 is a cross-sectional view of the converter lens RCL of the first embodiment.

FIG. 3 is an aberration diagram when focusing on an infinite object when the converter lens RCL of the first embodiment is arranged on the image side of the master lens ML.

In the converter lens RCL of the first embodiment, the negative lens Ln is the lens arranged on the image side most. Further, the converter lens RCL has a junction lens La composed of a negative lens arranged on the most object side and a positive lens arranged on the image side of the negative lens. Further, the converter lens RCL is composed of three positive lenses and four negative lenses, and has a configuration in which negative lenses and positive lenses are alternately arranged from the object side to the image side. The lens element Lp comprises a negative lens Ln and a positive lens arranged adjacent to the object side of the negative lens.

[Example 2]
FIG. 4 is a cross-sectional view of the converter lens RCL of the second embodiment.

FIG. 5 is an aberration diagram when focusing on an infinite object when the converter lens RCL of the second embodiment is arranged on the image side of the master lens ML.

In the converter lens RCL of the second embodiment, the negative lens Ln is the fifth lens arranged from the object side toward the image side. Further, the converter lens RCL has a junction lens La composed of a negative lens arranged on the most object side and a positive lens arranged on the image side of the negative lens. Further, the converter lens RCL is composed of four positive lenses and five negative lenses, and has a configuration in which negative lenses and positive lenses are alternately arranged from the object side to the image side. The lens element Lp consists of a negative lens arranged on the image side most and a positive lens arranged adjacent to the object side of the negative lens.

[Example 3]
FIG. 6 is a cross-sectional view of the converter lens RCL of the third embodiment.

FIG. 7 is an aberration diagram when focusing on an infinity object when the converter lens RCL of Example 3 is arranged on the image side of the master lens ML.

In the converter lens RCL of the third embodiment, the negative lens Ln is the second lens arranged from the image side toward the object side. Further, the converter lens RCL has a junction lens La composed of a negative lens arranged on the most object side and a positive lens arranged on the image side of the negative lens. Further, the converter lens RCL is composed of four positive lenses and five negative lenses, and has a configuration in which the negative lenses and the positive lenses are alternately arranged from the object toward the image side. The lens element Lp is composed of one positive lens arranged on the image side most.

By satisfying the above-mentioned conditional expressions (1) to (7) in all of the above Examples 1 to 3, high optical performance is realized while making the converter lens RCL compact.

[Numerical Example]
Numerical examples 1 to 3 corresponding to the above-mentioned master lens ML numerical examples and converter lens RCLs of Examples 1 to 3 are shown.

Further, in each numerical example, the surface number indicates the order of the optical surfaces from the object side. r is the radius of curvature (mm) of the optical surface, d in the surface number i is the distance between the i-th optical surface and the i + 1th optical surface (mm), and nd is the refractive index of the material of the optical member in the d line. νd is the Abbe number of the material of the optical member with respect to the d line. The definition of Abbe number is the same as above.
νd = (Nd-1) / (NF-NC)
Is.

BF indicates back focus. That is, the distance on the optical axis from the 30th plane of the master lens ML to the paraxial image plane is expressed by the air conversion length.

The total length of the lens in the numerical embodiment of the master lens ML is the length obtained by adding back focus to the distance on the optical axis from the first surface of the master lens ML to the thirty surface of the master lens ML.

The lens distance between the master lens ML and the converter lens RCL is a value obtained by expressing the distance on the optical axis from the 29th surface of the master lens ML to the first surface of the converter lens RCL in terms of air equivalent length.

The front principal point position is the distance from the most object-side surface to the front principal point, and the rear principal point position is the distance from the most image-side surface to the rear principal point. The numerical values for the front principal point position and the rear principal point position are paraxial amounts, and the reference numerals are positive from the object side to the image side.

Further, the values corresponding to the above-mentioned conditional expressions in each of the numerical examples 1 to 3 are shown in [Table 1].

[Master lens] -Numerical value of converter lens Common to Examples 1 to 3-
Unit mm

Surface data Surface number rd nd νd Effective diameter
1 292.465 15.81 1.48749 70.5 135.24
2 -517.524 29.13 134.70
3 145.749 21.85 1.43387 95.1 117.84
4-310.360 0.08 115.79
5 -309.759 4.30 1.65412 39.7 115.71
6 260.211 26.17 109.68
7 90.793 15.28 1.43387 95.1 97.33
8 529.656 0.25 95.31
9 67.742 6.00 1.48749 70.2 84.64
10 52.993 29.99 76.66
11 807.025 6.60 1.80810 22.8 67.30
12 -149.923 3.20 1.83400 37.2 66.45
13 132.030 81.82 62.43
14 (Aperture) ∞ 3.43 40.06
15 365.029 6.38 1.65160 58.5 38.93
16 -64.603 2.18 1.84666 23.8 38.29
17 -140.611 4.43 37.82
18 88.023 4.87 1.84666 23.8 36.27
19 -141.829 1.70 1.69680 55.5 35.85
20 40.372 5.33 34.07
21 -141.777 1.70 1.83481 42.7 34.17
22 95.226 3.39 35.10
23 99.547 5.56 1.80400 46.6 37.87
24-250.416 10.03 38.52
25 59.528 7.72 1.74951 35.3 42.44
26 -105.426 2.00 1.80810 22.8 42.14
27 107.015 4.26 41.17
28 ∞ 2.20 1.51633 64.1 41.24
29 ∞ 22.09 41.28
30 ∞ (mounting surface) 44.00 39.00
Image plane ∞

Various data focal length 392.18
F number 2.90
Half angle of view (degrees) 3.16
Image height 21.64
Total lens length 371.77
BF 44.00

[Converter lens]
[Numerical Example 1]
Unit mm

Surface data Surface number rd nd νd θgF Effective diameter mounting surface ∞ -0.99 (d0)-
1 -4057.992 1.30 1.95375 32.3 0.5898 28.58
2 86.537 4.22 1.67270 32.1 0.5988 28.66
3-68.909 6.79 28.81
4-63.746 1.30 1.72916 54.7 0.5444 27.93
5 31.820 8.17 1.59551 39.2 0.5803 28.65
6 -44.308 1.50 1.72916 54.7 0.5444 29.14
7 74.946 0.20 30.52
8 43.882 7.24 1.63980 34.5 0.5922 31.85
9 -56.710 2.00 2.31235 17.0 0.6502 32.09
10 -142.210 --32.95

Various data focal length -106.28
Magnification 1.40
d0 -0.99
Front principal point position 14.54
Rear principal point position -8.00
* Excluding the mounting surface

Single lens Data lens Start surface Focal length
1 1 -88.82
2 2 57.66
3 4 -28.94
4 5 32.40
5 6 -37.99
6 8 39.78
7 9 -72.84

Distance between the master lens and the converter lens of Numerical Example 1 21.10

[Numerical Example 2]
Unit mm

Surface data Surface number rd nd νd θgF Effective diameter mounting surface ∞ 2.22 (d0) 22.31
1 64.461 1.00 1.83481 42.7 0.5648 22.27
2 15.828 8.70 1.56732 42.8 0.5731 21.56
3 -43.333 1.57 21.92
4-56.804 1.00 1.77250 49.6 0.5520 21.71
5 21.046 4.94 1.75520 27.5 0.6103 22.28
6 487.651 8.87 22.51
7 -91.733 1.20 2.27615 18.2 0.6438 24.49
8 66.782 8.95 1.73800 32.3 0.5899 25.34
9 -20.173 0.19 26.63
10 -23.408 1.20 1.59282 68.6 0.5446 26.06
11 50.417 0.20 27.69
12 36.827 7.80 1.51742 52.4 0.5564 28.60
13 -39.781 1.40 1.83481 42.7 0.5648 28.96
14 -172.821 --29.89

Various data focal length -57.78
Magnification 2.00
d0 2.22
Front principal point position 12.89
Rear principal point position-19.76
* Excluding the mounting surface

Single lens Data lens Start surface Focal length
1 1 -25.37
2 3 21.58
3 5 -19.77
4 6 28.99
5 8 -30.16
6 9 21.95
7 11 -26.80
8 13 38.29
9 14 -62.20

Distance between the master lens and the converter lens of Numerical Example 2 24.31

[Numerical Example 3]
Unit mm

Surface data Surface number rd nd νd θgF Effective diameter mounting surface ∞ 1.56 (d0) 22.72
1 50.736 1.10 1.83481 42.7 0.5642 22.65
2 16.014 8.13 1.61340 44.3 0.5633 21.75
3-52.516 0.23 21.73
4-149.421 1.10 1.72916 54.7 0.5444 21.46
5 14.527 10.98 1.61293 37.0 0.5862 20.88
6 -20.821 1.20 1.72916 54.7 0.5444 21.03
7 27.668 0.56 21.76
8 26.365 3.80 1.60342 38.0 0.5835 22.68
9 188.945 3.16 22.92
10 -26.584 1.20 2.24680 19.8 0.6345 22.98
11 -101.243 4.51 24.99
12 -97.025 9.00 1.56732 42.8 0.5731 30.31
13 -20.932 --32.50

Various data focal length-100.42
Magnification 2.00
d0 1.56

Front principal point position -7.77
Rear principal point position -55.39
* Excluding the mounting surface

Single lens Data lens Start surface Focal length
1 1 -28.44
2 3 20.95
3 5 -18.11
4 6 15.83
5 7 -16.13
6 9 50.34
7 11 -29.17
8 13 45.11

Distance between the master lens and the converter lens of Numerical Example 3 23.65

[Example of imaging device]
FIG. 8 is a diagram showing a configuration of an imaging device (digital camera) 10. FIG. 8A is a perspective view, and FIG. 8B is a side view. The image pickup device 10 photoelectrically converts an image formed by the camera body 13, the master lens ML, the converter lens RCL similar to any one of Examples 1 to 3 described above, the master lens ML, and the converter lens RCL. A light receiving element (imaging element) 12 is provided. As the light receiving element 12, an image pickup element such as a CCD sensor or a CMOS sensor can be used. The master lens ML and the converter lens RCL may be integrally configured with respect to the camera body 13, or may be detachably configured with respect to the camera body 13.

When the master lens ML and the converter lens RCL are integrally configured with the camera body 13, the converter lens RCL is configured to be removable on the optical axis.

[Example of interchangeable lens]
The present invention can also be applied to an interchangeable lens in which the master lens ML and the converter lens RCL are configured in the same lens barrel and can be attached to and detached from the image pickup apparatus. The master lens ML may be a single focus lens or a zoom lens. In this case, the converter lens RCL is configured to be removable on the optical axis. The converter lens RCL is arranged on or off the optical axis in response to instructions from the user via the operating member or user interface.

Although preferred embodiments 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.

RCL converter lens ML master lens Ln negative lens

Claims (11)

It is a converter lens that has a negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone.
When the refractive index of the material on the d line is Nd and the Abbe number based on the d line is νd,
2.20 <Nd <2.37
13.00 <νd <23.00
A converter lens characterized by having a negative lens satisfying the conditional expression. The refractive index of the negative lens material at F, C, and g lines is NF, NC, and Ng, and the partial dispersion ratio θgF of the negative lens material is θgF = (Ng-NF) / (NF-NC).
When expressing
0.017 <θgF-0.6438 + 0.001682 × νd <0.040
The converter lens according to claim 1, wherein the converter lens satisfies the conditional expression. When the focal length of the converter lens is f and the focal length of the negative lens is fn,
0.25 <fn / f <1.00
The converter lens according to claim 1 or 2, wherein the converter lens satisfies the conditional expression. When the average refractive index of all the negative lens materials contained in the converter lens in the d line is Nd_ave,
1.80 <Nd_ave <2.00
The converter lens according to any one of claims 1 to 3, wherein the converter lens satisfies the conditional expression. The converter lens is composed of N lenses (N ≧ 1).
The focal length of the i-th (i = 1-N) lens of the converter lens counted from the object side is fi, and the d of the i-th (i = 1-N) lens of the converter lens counted from the object side. When the Abbe number with respect to the line is νdi,

The converter lens according to any one of claims 1 to 4, wherein the converter lens satisfies the conditional expression. The distance on the optical axis from the most object-side surface of the converter lens to the most image-side surface is TL, and the distance on the optical axis from the most object-side surface of the converter lens to the object-side surface of the negative lens. When is Dn
0.50 <Dn / TL <0.98
The converter lens according to any one of claims 1 to 5, wherein the converter lens satisfies the conditional expression. The converter lens according to any one of claims 1 to 6, further comprising a junction lens composed of a positive lens and a negative lens, which is arranged on the most object side of the converter lens. The converter lens consists of a plurality of positive lenses and a plurality of negative lenses.
The converter lens according to any one of claims 1 to 7, wherein the positive lens and the negative lens are alternately arranged on the optical axis. The converter lens according to any one of claims 1 to 8, further comprising a lens element having a positive refractive power, which is arranged on the most image side of the converter lens. An interchangeable lens comprising a master lens and a converter lens according to any one of claims 1 to 9. With the master lens
The converter lens according to any one of claims 1 to 10.
An image pickup device comprising an image pickup element that receives an image formed by the converter lens.