JP6337687B2 - Rear conversion lens - Google Patents

Description

  The present invention relates to a rear conversion lens that is attached to an image side of a photographing lens (main lens) used in a digital camera, a video camera, etc., and expands its focal length.

  Conventionally, a digital still camera has been implemented to displace the focal length in the longer direction by mounting a rear conversion lens between the interchangeable lens (main lens) and the camera body. The aberration of the composite system in which the rear conversion lens is attached to the main lens is a combination of the aberration of the main lens enlarged by the rear conversion lens and the aberration of the rear conversion lens. Therefore, in order to improve the image quality of the composite system in which the rear conversion lens is attached to the main lens, the rear conversion lens is required to reduce the aberration of the rear conversion lens itself.

  In general, if the number of pixels is the same, a large image sensor has a larger area per pixel than a small image sensor, so that a good image with less noise can be obtained. Therefore, digital still cameras, video cameras, and the like that employ a large image sensor in order to achieve high image quality are increasing in recent years. The imaging optical system used for the main lens is also compatible with a large image sensor used in the camera. However, as the image pickup device becomes larger, the imaging optical system tends to increase in size. Therefore, the rear conversion lens is required to be downsized.

  In recent years, it has been demanded to improve image quality when mounted on a bright telephoto lens of about F2.0.

  Patent Documents 1 and 2 disclose rear conversion lenses corresponding to a large image sensor and having a magnification of about 1.4 times.

JP 2011-081111 A JP-A-60-136712

  In the rear conversion lens in Patent Document 1, the chromatic aberration of magnification is favorably corrected by using a material with high dispersion and a large partial dispersion ratio for the negative lens. However, a material having a high dispersion and a large partial dispersion ratio has a low transmittance on the short wavelength side, so that the change in the color of transmitted light when the rear conversion lens is attached cannot be sufficiently reduced. In addition, since the effective diameter of the lens closest to the image plane is large, there is a problem that the risk of interference with the mechanism of the mount portion of the digital camera increases, and it is difficult to reduce the outer diameter of the lens barrel.

  The rear conversion lens in Patent Document 2 was designed with a F2.0 large-aperture telephoto lens as a reference objective lens. However, the lateral chromatic aberration of the rear conversion lens is not sufficiently corrected. In addition, since the aberration of the rear conversion lens is added to cancel the spherical aberration of the reference objective lens and the curvature of field and astigmatism, the aberration of the rear conversion lens when attached to the main lens with small aberration This causes a problem that the image quality is deteriorated.

  The present invention has been made in view of such a situation, and even when mounted on a bright telephoto lens of about F2.0, a good image quality is obtained, and a small rear conversion lens corresponding to a large image sensor. The purpose is to provide.

A first invention, which is a means for solving the above-described problems, is a rear conversion lens that is attached to the image side of a photographing lens and expands its focal length, and is joined in order from the object side to a negative lens and a positive lens. A first lens group having a positive refractive power, a second lens group having a negative refractive power composed of two negative lenses, and a positive refraction composed of at least a positive lens and a negative lens cemented lens and a positive lens. And a third lens group having power, wherein the negative lens closest to the object side of the second lens group satisfies the following conditional expression:
(1) 0.008 <θgFn2−0.64826 + 0.0018008 × νdn2
(2) 60 <νdn2
(3) 0.4 <fn2 / f <2.0
θgFn2: Partial dispersion ratio νdn2 of the negative lens closest to the object side of the second lens group: Abbe number fn2 of the d-line of the negative lens closest to the object side of the second lens group: Most object of the second lens group Focal length f of the negative lens on the side: Focal length of the rear conversion lens

The second invention, which is a means for solving the above-mentioned problems, is the rear conversion lens according to the first invention, and further satisfies the following conditional expression: .
(4) 0.55 <| f3 / f |
f3: focal length of the third lens group f: focal length of the rear conversion lens

The third invention, which is means for solving the above-mentioned problems, is the rear conversion lens of the first invention or the second invention, and further satisfies the following conditional expression: It is a rear conversion lens.
(5) 1.02 <N11 / N12 <1.25
N11: Refractive index of the negative lens of the first lens group N12: Refractive index of the positive lens of the first lens group

A fourth invention, which is a means for solving the above-described problems, is the rear conversion lens according to any one of the first to third inventions, and further satisfies the following conditional expression: Is a rear conversion lens characterized by
(6) 1.25 <β <1.55
β: magnification of the rear conversion lens

  According to the present invention, good image quality can be obtained even when attached to a bright telephoto lens of about F2.0, and a small rear conversion lens corresponding to a large image sensor can be provided.

Lens configuration diagram of the main lens used in each numerical example Longitudinal aberration diagram of main lens used in each numerical example Transverse aberration diagram of main lens used in each numerical example Lens configuration diagram when the rear conversion lens of Numerical Example 1 is attached to the main lens Lens configuration diagram of rear conversion lens of Numerical Example 1 Longitudinal aberration diagram when the rear conversion lens of Numerical Example 1 is attached to the main lens Transverse aberration diagram when the rear conversion lens of Numerical Example 1 is attached to the main lens Lens configuration diagram of rear conversion lens of Numerical Example 2 Longitudinal aberration diagram when the rear conversion lens of Numerical Example 2 is attached to the main lens Transverse aberration diagram when the rear conversion lens of Numerical Example 2 is attached to the main lens Lens configuration diagram of rear conversion lens of Numerical Example 3 Longitudinal aberration diagram when the rear conversion lens of Numerical Example 3 is attached to the main lens Transverse aberration diagram when the rear conversion lens of Numerical Example 3 is attached to the main lens Lens configuration diagram of rear conversion lens of Numerical Example 4 Longitudinal aberration diagram when the rear conversion lens of Numerical Example 4 is attached to the main lens Transverse aberration diagram when the rear conversion lens of Numerical Example 4 is attached to the main lens Lens configuration diagram of rear conversion lens of Numerical Example 5 Longitudinal aberration diagram when the rear conversion lens of Numerical Example 5 is attached to the main lens Lateral aberration diagram when the rear conversion lens of Numerical Example 5 is attached to the main lens

  The rear conversion lens of the present invention can be understood from the lens configuration diagrams of the rear conversion lenses of Examples 1 to 5 of the present invention shown in FIGS. 5, 8, 11, 14, and 17 as the first invention. As described above, in order from the object side, a first lens group having a positive refractive power formed by joining a negative lens and a positive lens, a second lens group having a negative refractive power formed by two negative lenses, and at least a positive lens And a third lens group having a positive refractive power and composed of a cemented lens of a negative lens and a positive lens.

  By adopting such a configuration, the negative Petzval sum of the second lens unit having a negative refractive power can be corrected by the first lens unit having a positive refractive power and the third lens unit having a positive refractive power. In addition, the spherical aberration of the second lens group can be effectively corrected by the first lens group having a relatively large axial beam diameter, and the positive distortion of the second lens group can be corrected. It is possible to correct effectively with the third lens group close to the image plane.

  In the present invention, conditional expressions (1) and (2) are set in consideration of the following. The secondary spectrum of lateral chromatic aberration generated in the rear conversion lens was suppressed by restricting the partial dispersion ratio and Abbe number of the negative lens closest to the object side in the second lens group. However, since this restriction lowers the refractive index of the negative lens, a technique using a high refractive index glass material cannot be used as a negative lens glass material, which is a technique for suppressing the shift of the Petzval sum of a general rear conversion lens to negative. Therefore, in the present invention, the shift of the Petzval sum to negative is suppressed by further configuring the second lens group as follows. That is, the image side surface of the negative lens at the head of the second lens group is set on the image side so that the axial distance between the negative lens on the object side of the second lens group having negative refractive power and the subsequent negative lens becomes large. On the other hand, the object side surface of the subsequent negative lens is concave with respect to the object side, and the distance between the lenses is greatly widened. The negative refractive power of the lens group can be secured, and the shift of the Petzval sum to negative is suppressed. This makes it possible to simultaneously suppress the generation of the secondary spectrum of lateral chromatic aberration and the negative shift of the Petzval sum.

  Furthermore, conditional expression (3) was set in consideration of the following. By defining the ratio of the focal length of the negative lens of the lens closest to the object of the second lens group and the focal length of the rear conversion lens, the secondary spectrum of lateral chromatic aberration generated in the rear conversion lens is reduced, and the spherical surface Occurrence of aberration and coma is suppressed, and sufficient optical performance can be obtained even when a large aperture telephoto lens of F2.0 is used as a reference objective lens.

  Furthermore, conditional expression (4) was set in consideration of the following. The present invention specifies the ratio of the focal length of the third lens group and the focal length of the rear conversion lens in order to avoid the risk of interference with the mechanism of the mount portion on the camera side and reduce the outer diameter of the lens barrel. It was possible to limit the effective diameter of the lens closest to the image side.

  Furthermore, conditional expression (5) was set in consideration of the following. In the present invention, by defining the ratio of the refractive index of the negative lens and the positive lens constituting the first lens group, the Petzval sum of the rear conversion lens can be maintained appropriately, and the occurrence of chromatic aberration can be suppressed and good image quality can be obtained. Made possible.

  Furthermore, conditional expression (6) was set in consideration of the following. In the present invention, the range in which a good image quality can be obtained is guaranteed by defining the magnification range of the rear conversion lens.

In addition, the rear conversion lens of the present invention satisfies the following conditional expressions (1) to (3).
(1) 0.008 <θgFn2−0.64826 + 0.0018008 × νdn2
(2) 60 <νdn2
(3) 0.4 <fn2 / f <2.0
θgFn2: Partial dispersion ratio νdn2 of the negative lens closest to the object side of the second lens group: Abbe number fn2 of the d-line of the negative lens closest to the object side of the second lens group: Most object of the second lens group Focal length f of the negative lens on the side: Focal length of the rear conversion lens

  Conditional expression (1) is the most preferable condition for the second lens group as a preferable condition for reducing the secondary spectrum of lateral chromatic aberration generated in the rear conversion lens and obtaining good image quality when the rear conversion lens is attached to the main lens. It defines the partial dispersion ratio of the negative lens on the object side.

  If the lower limit of conditional expression (1) is exceeded and the partial dispersion ratio of the negative lens becomes small, it becomes difficult to correct the secondary spectrum of lateral chromatic aberration that occurs in the rear conversion lens.

  Regarding conditional expression (1), the lower limit is desirably set to 0.019, and further to 0.030, the above-described effect can be further ensured.

  Conditional expression (2) is the most preferable condition for the second lens group as a preferable condition for reducing axial chromatic aberration and lateral chromatic aberration generated in the rear conversion lens and obtaining good image quality when the rear conversion lens is attached to the main lens. It defines the Abbe number of the negative lens on the object side.

  If the lower limit of conditional expression (2) is exceeded and the Abbe number of the negative lens becomes small, it is difficult to correct axial chromatic aberration and lateral chromatic aberration that occur in the rear conversion lens.

  Regarding conditional expression (2), the lower limit is desirably set to 65.0, and further to 75.0, whereby the above-described effect can be further ensured.

  Conditional expression (3) reduces the secondary spectrum of chromatic aberration of magnification generated in the rear conversion lens, suppresses the occurrence of spherical aberration and coma, and obtains good image quality when the rear conversion lens is attached to the main lens. As a preferable condition, the ratio between the focal length of the negative lens and the focal length of the rear conversion lens of the lens closest to the object in the second lens group is defined.

  When the lower limit of conditional expression (3) is exceeded and the focal length of the negative lens closest to the object in the second lens group becomes shorter, the curvature of the negative lens increases and the light beam incident on the negative lens is bent sharply. Therefore, spherical aberration and coma are generated, and it becomes difficult to obtain good image quality.

  When the upper limit of conditional expression (3) is exceeded and the focal length of the negative lens closest to the object side in the second lens group is increased, the secondary spectral correction effect of the negative lens is reduced, and the lateral chromatic aberration generated in the rear conversion lens It becomes difficult to correct the second order spectrum.

  Regarding conditional expression (3), the lower limit value is desirably set to 0.45, and the upper limit value is further set to 1.9, so that the above-described effect can be further ensured.

The rear conversion lens according to claim 1, further satisfying the following conditional expression.
(4) 0.55 <| f3 / f |
f3: focal length of the third lens group f: focal length of the rear conversion lens

  Conditional expression (4) defines the ratio between the focal length of the third lens group and the focal length of the rear conversion lens as a condition for limiting the effective diameter of the lens closest to the image side.

  If the lower limit of conditional expression (4) is exceeded and the focal length of the third lens group is shortened, the effective angle of the lens on the most image side is large because the exit angle of the off-axis light beam becomes loose due to strong positive refractive power. turn into.

  For conditional expression (4), the lower limit is preferably set to 0.60, and the upper limit is further set to 12.00, whereby the above-described effect can be further ensured.

  When a desirable upper limit value for conditional expression (4) is exceeded and the focal length of the third lens group is increased, negative Petzval sum and positive distortion occurring in the second lens group having negative refractive power are positive. It becomes difficult to correct by the third lens group having refractive power.

The rear conversion lens according to claim 1, wherein the following conditional expression is satisfied.
(5) 1.02 <N11 / N12 <1.25
N11: Refractive index of the negative lens of the first lens group N12: Refractive index of the positive lens of the first lens group

  Conditional expression (5) indicates that the refractive index of the negative lens of the first lens group and the refractive index of the positive lens of the first lens group are preferable conditions for maintaining the Petzval sum of the rear conversion lens appropriately and suppressing the occurrence of chromatic aberration. The ratio is specified.

  Since the rear conversion lens as a whole has a negative refractive power, a negative Petzval sum is produced. In order to correct the negative Petzval sum, it is necessary to use a high refractive index glass material for the negative lens and a low refractive index glass material for the positive lens. In the present invention, in order to efficiently suppress the negative Petzval sum, the second lens group is composed of two negative lenses. Therefore, the second lens group is not achromatic, and in order to correct the chromatic aberration, the chromatic aberration of the first lens group having a positive refractive power must be undercorrected. In order to shift the Petzval sum of the first lens group positively and make the chromatic aberration of the first lens group undercorrected, the glass materials of the positive lens and the negative lens must be appropriately selected.

  If the lower limit of conditional expression (5) is exceeded and the ratio of the refractive index of the negative lens of the first lens group to the refractive index of the positive lens of the first lens group becomes small, the Petzval sum of the rear conversion lens becomes insufficiently corrected. Correction of curvature of field, astigmatism, etc. becomes difficult.

  When the upper limit of conditional expression (5) is exceeded, the refractive index of the negative lens in the first lens group becomes high, and the refractive index of the positive lens in the first lens group becomes low, the negative lens is a high dispersion glass material and the positive lens is low Since only the dispersion glass material can be selected and the under chromatic aberration of the first lens group for canceling out the chromatic aberration of the second lens group itself cannot be generated, the chromatic aberration in the first and second lens group synthesis system is corrected. Can not.

  Regarding conditional expression (5), the lower limit value is desirably set to 1.04, and the upper limit value is further set to 1.20, whereby the above-described effect can be further ensured.

The rear conversion lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
(6) 1.25 <β <1.55
β: magnification of the rear conversion lens

  Conditional expression (6) defines the magnification of the rear conversion lens.

  When the lower limit value of conditional expression (6) is not reached, sufficient magnification cannot be secured as a rear conversion lens.

  If the upper limit value of conditional expression (6) is exceeded, the negative refractive power of the rear conversion lens becomes strong, and aberration correction becomes difficult.

  In conditional expression (6), the lower limit value is desirably set to 1.30, and the upper limit value is further set to 1.50, whereby the above-described effect can be further ensured.

  Next, a lens configuration of an example according to the imaging optical system of the present invention will be described. In the following description, the lens configuration is described in order from the object side to the image side.

  Specific numerical data of each embodiment of the rear conversion lens of the present invention described above will be shown below.

  In [Surface Data], the surface number is the number of the lens surface or aperture stop counted from the object side, r is the radius of curvature of each surface, d is the distance between the surfaces, and nd is for the d-line (wavelength λ = 587.56 nm). The refractive index, vd, indicates the Abbe number with respect to the d line.

  The (diaphragm) attached to the surface number indicates that the aperture stop is located at that position. ∞ (infinity) is entered in the radius of curvature for a plane or aperture stop.

  [Various data] indicates a value when the shooting distance is infinite (INF).

  [Variable interval data] indicates the value of the variable interval and BF (back focus) when the shooting distance is infinity (INF). D1 is the distance between the most image side surface of the main lens and the most object side surface of the rear conversion lens.

  In all the following specification values, the focal length f, the radius of curvature r, the lens surface interval d, and other length units described are in millimeters (mm) unless otherwise specified. However, since the same optical performance can be obtained in proportional enlargement and proportional reduction, it is not limited to this.

  Further, the lens configuration diagrams shown in FIGS. 5, 8, 11, 14, and 17 are lens configuration diagrams when the rear conversion lens of each embodiment of the present invention is mounted on the main lens. 1, 4, 5, 8, 11, 14, and 17, S is an aperture stop, I is an image plane, F is a filter, and a one-dot chain line that passes through the center is an optical axis.

  The main lens used in each example of the present invention is the imaging optical system disclosed in Example 1 of Japanese Patent Application Laid-Open No. 2008-14558. However, the main lens is not limited to this.

  In order to appropriately evaluate chromatic aberration in the examples, a known glass type was applied to Example 1 of Japanese Patent Application Laid-Open No. 2008-145584.

  The glass types of the main lens are the glass types of OHARA Co., Ltd. and Sumita Optical Glass Co., Ltd. (SUMITA).

The specification values of the imaging optical system of the main lens used in each example are shown below.
Main lens Unit: mm
[Surface data]
Surface number rd nd vd Glass type
1 469.6730 6.2300 1.48749 70.20 S-FSL5 (OHARA)
2 -105940.0000 0.5200
3 91.9260 18.4900 1.43387 95.10 K-CaFK95 (SUMITA)
4 -15019.2810 1.9400
5 82.8680 17.1200 1.49700 81.50 S-FPL51 (OHARA)
6 -583.6530 0.1000
7 -545.8800 4.4000 1.65412 39.70 S-NBH5 (OHARA)
8 159.3730 1.4900
9 92.9750 5.0000 1.69680 55.50 S-LAL14 (OHARA)
10 37.3600 14.8500 1.49700 81.50 S-FPL51 (OHARA)
11 135.8090 14.8700
12 -1035.9160 3.9700 1.84666 23.80 S-NPH53 (OHARA)
13 -101.5790 3.0000 1.77250 49.60 S-LAH66 (OHARA)
14 63.7130 26.4800
15 (Aperture) ∞ 4.4400
16 124.2420 2.1000 1.65412 39.70 S-NBH5 (OHARA)
17 41.6660 9.3800 1.77250 49.60 S-LAH66 (OHARA)
18 -320.1080 2.7500
19 -392.9170 1.9000 1.69680 55.50 S-LAL14 (OHARA)
20 63.9480 3.9300
21 -114.5970 4.0100 1.84666 23.80 S-NPH53 (OHARA)
22 -40.9430 1.9000 1.54072 47.20 S-TIL2 (OHARA)
23 81.9900 3.0300
24 104.8090 8.0100 1.72916 54.70 S-LAL18 (OHARA)
25 -41.1240 2.0000 1.80518 25.40 S-TIH6 (OHARA)
26 -347.9880 0.2000
27 72.3650 3.7300 1.80400 46.60 S-LAH65 (OHARA)
28 518.3480 3.2700
29 ∞ 2.0000 1.51633 64.10 S-BSL7 (OHARA)
30 ∞ (BF)

[Various data]
INF
Focal length 194.93
F number 2.05
Full angle of view 2ω 12.70
Statue height Y 21.63
Total lens length 231.33

[Variable interval data]
INF
BF 60.2233

  FIG. 5 is a lens configuration diagram of the rear conversion lens of Example 1 of the present invention. The rear conversion lens according to the first embodiment of the present invention includes a first lens group, a second lens group, and a third lens group in order from the object, and the first lens group has a positive refractive power as a whole. A cemented lens in which a meniscus first lens having a negative refractive power with a convex surface facing the object side and a second lens having a biconvex positive refractive power are bonded together, and the second lens group as a whole A meniscus third lens having a negative refractive power and having a negative refractive power with a convex surface facing the object side, and a meniscus fourth lens having a negative refractive power with a concave surface facing the object side The third lens group has a positive refractive power as a whole, and a biconvex fifth lens having a positive refractive power and a biconcave sixth lens having a negative refractive power are attached. The combined cemented lens and a seventh lens having a biconvex positive refractive power. Consisting of a's.

Subsequently, specification values of the rear conversion lens according to Example 1 are shown below.
Numerical example 1
Unit: mm
[Surface data]
Surface number rd nd vd
1 ∞ (d1)
2 59.8100 0.8000 1.88100 40.14
3 26.2200 7.0500 1.60342 38.01
4 -96.4600 0.1500
5 210.0000 0.8000 1.49700 81.61
6 32.4600 5.5900
7 -43.4900 0.8000 1.72916 54.67
8 -1000.0000 0.3000
9 43.1700 7.3500 1.58144 40.89
10 -43.1700 0.8000 1.95375 32.32
11 251.0000 0.9000
12 208.5000 3.3000 1.54814 45.82
13 -101.8000 (BF)

[Various data]
INF
Focal length 274.52
F number 2.89
Full angle of view 2ω 9.06
Statue height Y 21.63
Total lens length 252.18

[Variable interval data]
INF
d1 13.7230
BF 39.5088

  FIG. 8 is a lens configuration diagram of the rear conversion lens of Example 2 of the present invention. The rear conversion lens of Example 2 of the present invention includes a first lens group, a second lens group, and a third lens group in order from the object, and the first lens group has a positive refractive power as a whole. A cemented lens in which a meniscus first lens having a negative refractive power with a convex surface facing the object side and a second lens having a biconvex positive refractive power are bonded together, and the second lens group as a whole A third lens having negative refracting power and having a birefringent negative refracting power and a meniscus fourth lens having a negative refracting power with the concave surface facing the object side; The lens group has a positive refractive power as a whole, and a cemented lens obtained by bonding a biconvex fifth lens having a positive refractive power and a biconcave sixth lens having a negative refractive power; And a biconvex seventh lens having positive refractive power.

Subsequently, specification values of the rear conversion lens according to Example 2 are shown below.
Numerical example 2
Unit: mm
[Surface data]
Surface number rd nd vd
1 ∞ (d1)
2 66.0190 0.8000 1.95375 32.32
3 35.3830 6.1820 1.67270 32.17
4 -91.7020 0.2040
5 -931.7020 0.8000 1.59282 68.63
6 32.8170 5.4690
7 -44.7230 0.8000 1.88100 40.14
8 -100.8890 0.3000
9 50.4050 7.8520 1.62004 36.30
10 -31.4180 0.8000 1.90366 31.32
11 98.6600 0.1500
12 59.7110 4.0510 1.58144 40.89
13 -237.9460 (BF)

[Various data]
INF
Focal length 271.75
F number 2.86
Full angle of view 2ω 9.17
Statue height Y 21.63
Total lens length 252.05

[Variable interval data]
INF
d1 13.7230
BF 39.8110

  FIG. 11 is a lens configuration diagram of the rear conversion lens of Example 3 of the present invention. The rear conversion lens of Example 3 of the present invention is composed of a first lens group, a second lens group, and a third lens group in order from the object, and the first lens group has a positive refractive power as a whole. A cemented lens in which a meniscus first lens having a negative refractive power with a convex surface facing the object side and a second lens having a biconvex positive refractive power are bonded together, and the second lens group as a whole A third meniscus lens having negative refractive power and having negative refractive power with a convex surface facing the object side, and a fourth lens having negative refractive power having a biconcave shape, The lens group has a positive refractive power as a whole, and a cemented lens obtained by bonding a biconvex fifth lens having a positive refractive power and a biconcave sixth lens having a negative refractive power; And a biconvex seventh lens having positive refractive power.

Subsequently, specification values of the rear conversion lens according to Example 3 are shown below.
Numerical Example 3
Unit: mm
[Surface data]
Surface number rd nd vd
1 ∞ (d1)
2 210.4920 0.8000 1.72342 37.99
3 30.5280 6.5890 1.64769 33.84
4 -99.8290 0.1500
5 44.8550 0.8000 1.43700 95.10
6 29.3030 5.1840
7 -75.8580 0.8000 1.88100 40.14
8 117.7360 0.3000
9 50.6340 7.2060 1.64769 33.84
10 -34.7390 0.8000 1.95375 32.32
11 146.3490 0.1500
12 70.3300 3.4420 1.56732 42.84
13 -349.6400 (BF)

[Various data]
INF
Focal length 271.72
F number 2.86
Full angle of view 2ω 9.11
Statue height Y 21.63
Total lens length 251.06

[Variable interval data]
INF
d1 13.7230
BF 40.0044

  FIG. 14 is a lens configuration diagram of the rear conversion lens of Example 4 of the present invention. The rear conversion lens of Example 4 of the present invention is composed of a first lens group, a second lens group, and a third lens group in order from the object, and the first lens group has a positive refractive power as a whole. A cemented lens in which a meniscus first lens having a negative refractive power with a convex surface facing the object side and a second lens having a biconvex positive refractive power are bonded together, and the second lens group as a whole A third meniscus lens having negative refractive power and having negative refractive power with a convex surface facing the object side, and a fourth lens having negative refractive power having a biconcave shape, The lens group has a positive refractive power as a whole, and a cemented lens obtained by bonding a biconvex fifth lens having a positive refractive power and a biconcave sixth lens having a negative refractive power; And a biconvex seventh lens having positive refractive power.

Subsequently, specification values of the rear conversion lens according to Example 4 are shown below.
Numerical Example 4
Unit: mm
[Surface data]
Surface number rd nd vd
1 ∞ (d1)
2 62.2260 0.8000 1.95375 32.32
3 26.4420 6.7050 1.67270 32.17
4 -137.9460 2.9160
5 1151.0430 0.8000 1.49700 81.61
6 46.9200 4.1970
7 -55.4650 0.8000 1.88100 40.14
8 119.2010 0.3000
9 76.6530 5.4880 1.64769 33.84
10 -50.6120 0.8000 1.95375 32.32
11 194.7300 0.1500
12 80.7560 4.9180 1.54814 45.82
13 -61.1020 (BF)

[Various data]
INF
Focal length 271.97
F number 2.86
Full angle of view 2ω 9.07
Statue height Y 21.63
Total lens length 251.07

[Variable interval data]
INF
d1 13.7230
BF 38.3621

  FIG. 17 is a lens configuration diagram of the rear conversion lens of Example 5 of the present invention. The rear conversion lens of Example 5 of the present invention includes a first lens group, a second lens group, and a third lens group in order from the object, and the first lens group has a positive refractive power as a whole. A cemented lens in which a meniscus first lens having a negative refractive power with a convex surface facing the object side and a second lens having a biconvex positive refractive power are bonded together, and the second lens group as a whole A third meniscus lens having negative refractive power and having negative refractive power with a convex surface facing the object side, and a fourth lens having negative refractive power having a biconcave shape, The lens group has a positive refractive power as a whole, and a cemented lens obtained by bonding a biconvex fifth lens having a positive refractive power and a biconcave sixth lens having a negative refractive power; And a biconvex seventh lens having positive refractive power.

Subsequently, specification values of the rear conversion lens according to Example 5 are shown below.
Numerical Example 5
Unit: mm
[Surface data]
Surface number rd nd vd
1 ∞ (d1)
2 72.7850 0.8000 1.95375 32.32
3 28.5570 6.5010 1.68893 31.16
4 -122.9250 0.1500
5 121.3020 0.8000 1.43700 95.10
6 40.1480 4.0630
7 -84.2270 0.8000 1.88100 40.14
8 391.9530 0.3000
9 96.1130 5.6220 1.62588 35.74
10 -39.4780 0.8000 1.91082 35.25
11 99.6230 0.1500
12 53.4330 3.5840 1.54814 45.82
13 -1506.4730 (BF)

[Various data]
INF
Focal length 271.71
F number 2.86
Full angle of view 2ω 9.06
Statue height Y 21.63
Total lens length 250.23

[Variable interval data]
INF
d1 13.7230
BF 41.8260

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

[Values for conditional expressions]
Conditional expression / Example 1 2 3
(1) 0.008 <θgFn2-0.64826 + 0.0018008 × νdn2 0.0375 0.0194 0.0564
(2) 60 <νdn2 81.61 68.63 95.10
(3) 0.4 <fn2 / f <2.0 0.67 0.46 1.80
(4) 0.55 <| f3 / f | 0.94 1.31 1.23
(5) 1.02 <N11 / N12 <1.25 1.17 1.17 1.05
(6) 1.25 <β <1.55 1.41 1.39 1.39

Conditional expression / Example 4 5
(1) 0.008 <θgFn2-0.64826 + 0.0018008 × νdn2 0.0375 0.0564
(2) 60 <νdn2 81.61 95.10
(3) 0.4 <fn2 / f <2.0 0.83 1.26
(4) 0.55 <| f3 / f | 0.65 10.00
(5) 1.02 <N11 / N12 <1.25 1.17 1.16
(6) 1.25 <β <1.55 1.40 1.39

ML Main lens F Filter RCL Rear conversion lens G1 First lens group G2 Second lens group G3 Third lens group I Image plane S Aperture stop

Claims (4)

A rear conversion lens that is mounted on the image side of the photographic lens and expands its focal length, and includes a first lens group having a positive refractive power composed of a negative lens and a positive lens in order from the object side, and two sheets A second lens group having a negative refractive power composed of a negative lens; and a third lens group having a positive refractive power composed of at least a cemented lens of a positive lens and a negative lens and a positive lens; The most object side negative lens of
A rear conversion lens satisfying the following conditional expression:
(1) 0.008 <θgFn2−0.64826 + 0.0018008 × νdn2
(2) 60 <νdn2
(3) 0.4 <fn2 / f <2.0
θgFn2: Partial dispersion ratio νdn2 of the negative lens closest to the object side of the second lens group: Abbe number fn2 of the d-line of the negative lens closest to the object side of the second lens group: Most object of the second lens group Focal length f of the negative lens on the side: Focal length of the rear conversion lens The rear conversion lens according to claim 1, wherein the following conditional expression is satisfied.
(4) 0.55 <| f3 / f |
f3: focal length of the third lens group f: focal length of the rear conversion lens The rear conversion lens according to claim 1, wherein the following conditional expression is satisfied.
(5) 1.02 <N11 / N12 <1.25
N11: Refractive index of the negative lens of the first lens group N12: Refractive index of the positive lens of the first lens group The rear conversion lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
(6) 1.25 <β <1.55
β: magnification of the rear conversion lens

Images