JP7195608B2 - rear conversion lens - Google Patents

Description

The present invention relates to a rear conversion lens that is mounted on the image side of a photographing lens (main lens) used in digital still cameras, video cameras, etc., and that enlarges the focal length of the lens.

Conventionally, there has been known a rear conversion lens that is detachably mounted between a main lens and a camera body to change the focal length of the entire system to be longer than the focal length of the main lens alone.

JP 2010-191211 A JP 2016-177042 A

In recent years, the quick return mirror has been abolished, and mirrorless camera systems, which have a shorter flange focal length than single-lens reflex cameras and are advantageous for miniaturization as a system, have gained popularity. The number of mirrorless camera systems equipped with this technology is also increasing. There is a demand for a compact rear conversion lens with high imaging performance suitable for a mirrorless camera system having such a large image sensor.

The rear conversion lens described in Patent Document 1 assumes a long flange back of a single-lens reflex camera system, and when mounted on a main lens with a short flange back for a mirrorless camera system, the distance between the main lens and the principal point is becomes larger and the magnification becomes smaller.

The rear conversion lens described in Patent Document 2 is intended for use in a mirrorless camera system, but the examples are only optical systems for relatively small image sensors. When scaled for a large image pickup device, the applicable flange back becomes long, so it cannot be said to be suitable for a mirrorless camera system having a large image pickup device.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact rear conversion lens having a short flange focal length, a large image pickup element, and a high imaging performance. With the goal.

A first invention for solving the above-mentioned problems is a rear conversion lens that is detachably mounted on the image side of a main lens and expands the focal length thereof, the rear conversion lens having positive refractive power in order from the object side. It consists of one lens group, a second lens group with negative refractive power, a third lens group with positive or negative refractive power, and a fourth lens group with positive refractive power, each lens group consisting of one lens or A rear conversion lens comprising a pair of cemented lenses, wherein the third lens group has one negative lens, and which satisfies the following conditional expression.
(1) 0.40≤BF/h≤1.10
(2) 0.80≦(L-PPO)/L≦1.70
(3) -1.00 ≤ (L + PPI) / L ≤ 0.20
(4) 0.10≤f123/f≤0.60
(6) nd3n≧1.97
however,
BF: back focus with the rear conversion lens attached to the main lens h: maximum image height L: distance from the lens surface closest to the object side of the rear conversion lens to the lens surface closest to the image side PPO: the rear Distance from the most object-side lens surface of the conversion lens to the object-side principal point of the rear conversion lens (the direction from the object side to the image side is positive.)
PPI: Distance from the most image side lens surface of the rear conversion lens to the image side principal point of the rear conversion lens (the direction from the object side to the image side is positive.)
f123: combined focal length from the first lens group to the third lens group f: focal length of the entire rear conversion lens system
nd3n: refractive index for the d-line of the negative lens included in the third lens group

A second invention, which is a means for solving the above-mentioned problems, is a rear conversion lens according to the first invention, characterized in that it further satisfies the following conditional expression: be.
(5) -0.30≤f2/f3≤0.30
however,
f2: focal length of the second lens group f3: focal length of the third lens group

A third invention for solving the above-mentioned problems is a rear conversion lens according to the first invention or the second invention, wherein the rear conversion lens further satisfies the following conditional expression: is the lens.
(7) (D34-PPI123+PPO4)/(-f)≧0.100
however,
D34: Air gap between the third lens group and the fourth lens group PPI123: Image of the combined system of the first lens group to the third lens group from the lens surface closest to the image side of the third lens group Distance to the side principal point (The direction from the object side to the image side is positive.)
PPO4: Distance from the most object-side lens surface of the fourth lens group to the object-side principal point of the fourth lens group (the direction from the object side to the image side is positive.)
f: focal length of the entire rear conversion lens system

A fourth invention, which is means for solving the above-mentioned problems, is the rear conversion lens according to any one of the first invention to the third invention, wherein the fourth lens group comprises one lens. is a positive meniscus lens with a convex surface facing the image side, and is characterized by satisfying the following conditional expression.
(8) 0.15≦RG4rear/f≦0.50
(9) -8.00 ≤ (RG4 rear + RG4 front) / (RG4 rear - RG4 front) ≤ -1.20
however,
RG4rear: radius of curvature of the lens surface of the fourth lens group closest to the image side RG4front: radius of curvature of the lens surface closest to the object side of the fourth lens group f: focal length of the entire rear conversion lens system

A fifth invention, which is means for solving the above-mentioned problems, is a rear conversion lens according to any one of the first invention to the fourth invention, which further satisfies the following conditional expression: It is a rear conversion lens characterized by
(10) S0*HG1*β/h≧21.0
however,
S0: Distance from the lens surface closest to the object side of the rear conversion lens to the imaging plane of the main lens (the direction from the object side to the image side is positive.)
HG1: effective ray height β on the lens surface closest to the object side of the rear conversion lens: magnification h of the rear conversion lens: maximum image height

A sixth invention, which is a means for solving the above-mentioned problems, is a rear conversion lens according to any one of the first invention to the fifth invention, which further satisfies the following conditional expression: It is a rear conversion lens characterized by
(11) 1.85≤β≤2.15
however,
β: magnification of the rear conversion lens

A seventh invention, which is a means for solving the above-mentioned problems, is the rear conversion lens according to any one of the first invention to the sixth invention, wherein the first lens group is an object-side lens. The second lens group consists of a set of three cemented lenses formed by cementing a negative lens, a positive lens, and a negative lens in order from the object side, and the second lens group is a set of cemented negative and positive lenses in order from the object side. The rear conversion lens is characterized in that it comprises a cemented lens, and the third lens group comprises a cemented lens set in which a positive lens and a negative lens are cemented in order from the object side.

According to the present invention, it is possible to provide a rear conversion lens that has a short flange focal distance, is compatible with a mirrorless camera system having a large image sensor, and is compact and has high imaging performance.

4 is a lens configuration diagram of a main lens used in each example. FIG. FIG. 4 is a longitudinal aberration diagram of the main lens used in each example. FIG. 4 is a lateral aberration diagram of a main lens used in each example. 2 is a lens configuration diagram when the rear conversion lens of Example 1 is attached to the main lens; FIG. 1 is a lens configuration diagram of a rear conversion lens of Example 1. FIG. 4 is a longitudinal aberration diagram when the rear conversion lens of Example 1 is attached to the main lens; FIG. 4 is a lateral aberration diagram when the rear conversion lens of Example 1 is attached to the main lens; FIG. FIG. 10 is a lens configuration diagram of a rear conversion lens of Example 2; FIG. 10 is a longitudinal aberration diagram when the rear conversion lens of Example 2 is attached to the main lens; FIG. 10 is a lateral aberration diagram when the rear conversion lens of Example 2 is attached to the main lens; FIG. 11 is a lens configuration diagram of a rear conversion lens of Example 3; FIG. 10 is a longitudinal aberration diagram when the rear conversion lens of Example 3 is attached to the main lens; FIG. 11 is a lateral aberration diagram when the rear conversion lens of Example 3 is attached to the main lens; FIG. 11 is a lens configuration diagram of a rear conversion lens of Example 4; FIG. 11 is a longitudinal aberration diagram when the rear conversion lens of Example 4 is attached to the main lens; FIG. 12 is a lateral aberration diagram when the rear conversion lens of Example 4 is attached to the main lens;

As can be seen from the lens configuration diagrams shown in FIGS. 5, 8, 11 and 14, the rear conversion lens of the present invention has a first lens group having positive refractive power and a negative refractive power in order from the object side. a second lens group with positive or negative refractive power, a third lens group with positive or negative refractive power, and a fourth lens group with positive refractive power, each lens group consisting of one lens or a set of cemented lenses consists of
Further, the rear conversion lens of the present invention is characterized by satisfying the following conditional expressions.
(1) 0.40≤BF/h≤1.10
(2) 0.80≦(L-PPO)/L≦1.70
(3) -1.00 ≤ (L + PPI) / L ≤ 0.20
(4) 0.10≤f123/f≤0.60
however,
BF: back focus with the rear conversion lens attached to the main lens h: maximum image height L: distance from the lens surface closest to the object side of the rear conversion lens to the lens surface closest to the image side PPO: the rear Distance from the most object-side lens surface of the conversion lens to the object-side principal point of the rear conversion lens (the direction from the object side to the image side is positive.)
PPI: Distance from the most image side lens surface of the rear conversion lens to the image side principal point of the rear conversion lens (the direction from the object side to the image side is positive.)
f123: combined focal length from the first lens group to the third lens group f: focal length of the entire rear conversion lens system

A rear conversion lens that changes the focal length of the main lens to a longer one has a negative refractive power as a whole system. In a mirrorless camera system with a short flange focal distance, the rear conversion lens is positioned close to the focal point of the main lens, so the entire rear conversion lens system must have a strong negative refractive power in order to obtain the necessary magnification. Become.
The outline of the reason is shown below.
Considering the thin-walled approximation, when the distance from the rear conversion lens to the image forming point of the main lens is S, the focal length of the rear conversion lens is f, and the magnification of the rear conversion lens is β, from the deformation of Newton's imaging formula , the following (reference formula a) holds.
(Reference formula a) S = (1/β-1) * f
When the enlargement magnification β is constant (β>1), the absolute value of f decreases as S decreases. That is, when the rear conversion lens is arranged at a position close to the image forming point of the main lens, it is necessary to increase the negative refractive power of the rear conversion lens in order to maintain the magnification.

In the rear conversion lens of the present invention, the combined system of the second lens group and the third lens group has a strong negative refractive power, and various aberrations caused by the strong negative refractive power are Correction is performed by the first lens group and the fourth lens group. The spherical aberration and axial chromatic aberration of the second lens group and the third lens group are corrected by the first lens group having a relatively large axial light beam diameter. In addition, the fourth lens group, which has a small on-axis ray diameter and a large off-axis ray height, greatly contributes to correction of curvature of field, astigmatism, and positive distortion of the second and third lens groups. , and correction is performed by both the first lens group and the fourth lens group.

Conditional expression (1) is for a mirrorless camera system with a large image sensor, in which the rear conversion lens is attached to the main lens in order to achieve a compact rear conversion lens while ensuring an appropriate back focus. It defines a preferable range for the ratio between the back focus and the maximum image height.

If the back focus with the rear conversion lens attached to the main lens increases beyond the upper limit of conditional expression (1), the total length of the rear conversion lens increases, making miniaturization difficult. On the other hand, if the lower limit of conditional expression (1) is exceeded and the back focus becomes too small with the rear conversion lens attached to the main lens, the back focus becomes insufficient, making it difficult to apply to a mirrorless camera system. .

By restricting the lower limit to 0.50 and the upper limit to 1.00 for conditional expression (1), the above effects can be more reliably achieved.

Conditional expression (2) defines a preferable range for the position of the object-side principal point of the rear conversion lens. By bringing the object-side principal point closer to the main lens, the distance between the principal points of the main lens and the rear conversion lens becomes smaller, making it possible to obtain a desired magnification with a smaller negative refractive power. By reducing the negative refractive power of the rear conversion lens, the amount of various aberrations generated is suppressed, making it easier to achieve high imaging performance.

When the position of the principal point on the object side approaches the image side beyond the lower limit of conditional expression (2), the distance between the principal points of the main lens and the rear conversion lens increases. The negative refractive power of the conversion lens increases. As a result, the amount of various aberrations generated increases, making it difficult to achieve high imaging performance. On the other hand, in order to exceed the upper limit of conditional expression (2) and bring the position of the principal point on the object side closer to the object side, the rear conversion lens must have a negative refractive power on the front side and a positive refractive power on the rear side. It is necessary to increase the asymmetry of the arrangement. As a result, various aberrations generated in each group increase, making it difficult to achieve high imaging performance.

By limiting the lower limit to 1.00 and the upper limit to 1.50 for conditional expression (2), the above effects can be more reliably achieved.

Conditional expression (3) defines a preferable range for the position of the image-side principal point of the rear conversion lens. The distance from the image-side principal point of the rear conversion lens to the imaging plane is determined by the magnification and focal length of the rear conversion lens. When the distance from the image-side principal point to the imaging plane is constant, the back focus changes depending on the position of the image-side principal point. By arranging the position of the image-side principal point closer to the object side, it becomes easier to reduce the back focus and downsize the rear conversion lens.

If the upper limit of conditional expression (3) is exceeded and the position of the image-side principal point approaches the image side, the back focus increases, making it difficult to reduce the size of the rear conversion lens. On the other hand, when the position of the image-side principal point approaches the object side beyond the lower limit of conditional expression (3), application to a mirrorless camera system becomes difficult due to insufficient back focus.

By restricting the lower limit to −0.80 and the upper limit to 0.00 for conditional expression (3), the above effects can be more reliably achieved.

Conditional expression (4) defines a preferable range for the ratio of the combined focal length of the first to third lens groups to the focal length of the entire rear conversion lens system. Negative refractive power is placed in the combined system of the first to third lens groups, positive refractive power is placed in the fourth lens group, and negative refractive power is placed near the object side of the entire rear conversion lens system. By arranging the refracting power in which the refracting power is positive on the side, it becomes easy to bring the object-side principal point and the image-side principal point of the rear conversion lens closer to the object side.

If the negative refractive power of the first to third lens groups becomes weaker than the upper limit of conditional expression (4), the object-side principal point and image-side principal point of the rear conversion lens move closer to the image side. As a result, as described above, it becomes difficult to achieve high imaging performance and miniaturization. On the other hand, if the negative refractive power of the first to third lens groups becomes too strong beyond the lower limit of conditional expression (4), it becomes difficult to correct various aberrations caused by the strong negative refractive power. , it becomes difficult to achieve high imaging performance.

By limiting the lower limit to 0.20 and the upper limit to 0.50 for conditional expression (4), the above effect can be more reliably achieved.

Further, in the rear conversion lens of the present invention, it is desirable that the third lens group has one negative lens and satisfies the following conditional expression.
(5) -0.30≤f2/f3≤0.30
(6) nd3n≧1.97
however,
f2: focal length of the second lens group f3: focal length of the third lens group nd3n: refractive index for the d-line of the negative lens included in the third lens group

Conditional expression (5) defines a preferable range for the ratio of the focal length of the second lens group to the focal length of the third lens group. The second lens group and the third lens group have a strong negative refractive power as a composite system. becomes closer to the image side, making it difficult to bring the positions of the object-side principal point and the image-side principal point of the rear conversion lens closer to the object side. Therefore, it is desirable to place a strong negative refractive power in the second lens group and a weak positive or negative refractive power in the third lens group.

If the negative refractive power of the third lens group becomes too strong beyond the upper limit of conditional expression (5), it will be difficult to bring the positions of the object-side principal point and the image-side principal point of the rear conversion lens closer to the object side. become. On the other hand, when the lower limit of conditional expression (5) is exceeded and the positive refractive power of the third lens group becomes too strong, the negative refractive power of the second lens group is increased in order to maintain the negative refractive power of the entire system. must be increased, various aberrations generated in the second lens group become large, and it becomes difficult to achieve high imaging performance.

By restricting the lower limit to -0.20 and the upper limit to 0.20 for conditional expression (5), the above effect can be more assured.

Conditional expression (6) relates to the refractive index of the material of the negative lens included in the third lens group. By using a material with a high refractive index for the negative lens of the third lens group, it becomes easy to suppress the Petzval sum generated in the composite system of the second lens group and the third lens group. Rather than using a material with a high refractive index for the second lens group, it is better to use it for the third lens group, which has a relatively small axial beam diameter and a high peripheral principal ray height, in order to correct curvature of field and astigmatism. is desirable.

When the refractive index of the material of the negative lens included in the third lens group becomes smaller than the lower limit of conditional expression (6), the negative Petzval sum generated in the composite system of the second lens group and the third lens group becomes This makes it difficult to satisfactorily correct curvature of field and astigmatism, making it difficult to achieve high imaging performance.

By limiting the lower limit of conditional expression (6) to 2.02, the above effect can be more reliably obtained.

Furthermore, the rear conversion lens of the present invention preferably satisfies the following conditional expressions.
(7) (D34-PPI123+PPO4)/(-f)≧0.100
however,
D34: Air gap between the third lens group and the fourth lens group PPI123: Image of the combined system of the first lens group to the third lens group from the lens surface closest to the image side of the third lens group Distance to the side principal point (The direction from the object side to the image side is positive.)
PPO4: Distance from the most object-side lens surface of the fourth lens group to the object-side principal point of the fourth lens group (the direction from the object side to the image side is positive.)
f: focal length of the entire rear conversion lens system

Conditional expression (7) relates to the distance from the image-side principal point of the combined system of the first to third lens groups to the object-side principal point of the fourth lens group. By increasing the distance between the principal points of the negative refractive power of the composite system of the first to third lens groups and the positive refractive power of the fourth lens group, the object-side principal point and the image-side principal point of the rear conversion lens It becomes easy to bring the point closer to the object side.

When the distance from the image-side principal point of the combined system of the first to third lens groups to the object-side principal point of the fourth lens group becomes smaller than the lower limit of conditional expression (7), The principal point on the object side and the principal point on the image side become closer to the image side, and as a result, it becomes difficult to realize high imaging performance and miniaturization as described above.

By limiting the lower limit of conditional expression (7) to 0.150, the above effect can be more reliably obtained.

Further, in the rear conversion lens of the present invention, it is desirable that the fourth lens group is composed of one positive meniscus lens having a convex surface facing the image side, and satisfies the following conditional expression.
(8) 0.15≦RG4rear/f≦0.50
(9) -8.00 ≤ (RG4 rear + RG4 front) / (RG4 rear - RG4 front) ≤ -1.20
however,
RG4rear: radius of curvature of the lens surface of the fourth lens group closest to the image side RG4front: radius of curvature of the lens surface closest to the object side of the fourth lens group f: focal length of the entire rear conversion lens system

Conditional expression (8) defines a preferable range for the ratio of the radius of curvature of the lens surface closest to the image side in the fourth lens group to the focal length of the entire rear conversion lens system. Since the lens surface of the fourth lens group closest to the image side is a strongly convex surface, it becomes easy to correct the negative Petzval sum generated in the second lens group and the third lens group.

If the radius of curvature of the lens surface closest to the image side in the fourth lens group exceeds the upper limit of conditional expression (8), the Petzval sum cannot be sufficiently corrected, making it difficult to achieve high imaging performance. become.
On the other hand, if the radius of curvature of the lens surface closest to the image side of the fourth lens group becomes too small beyond the lower limit of conditional expression (8), the overall length and weight of the fourth lens group increase, making miniaturization difficult. become.

By restricting the lower limit to 0.20 and the upper limit to 0.40 for conditional expression (8), the above effects can be more reliably achieved.

Conditional expression (9) defines a preferable range for the shape factor of the fourth lens group. The fourth lens group has a positive meniscus shape with a convex surface facing the image side, so that the object-side principal point of the fourth lens group can be shifted toward the image side, and the first to third lens groups By increasing the distance between the principal points of the combined system and the fourth lens group, it becomes easy to bring the object-side principal point and the image-side principal point of the rear conversion lens closer to the object side.

If the upper limit of conditional expression (9) is exceeded and the lens shape of the fourth lens group approaches a plano-convex shape, the object-side principal point of the fourth lens group will be shifted to the object side, The reduction in the distance between the principal points of the combined system of the three lens groups and the fourth lens group makes it difficult to bring the object-side principal point and the image-side principal point of the rear conversion lens closer to the object side. On the other hand, if the lower limit of conditional expression (9) is exceeded and the lens shape of the fourth lens group becomes too extreme a meniscus shape, the positive refracting power of the fourth lens group becomes small, resulting in curvature of field and non-uniformity. Good correction of astigmatism and distortion becomes difficult.

By restricting the lower limit to −6.00 and the upper limit to −1.50 for conditional expression (9), the above effect can be more reliably obtained.

Furthermore, the rear conversion lens of the present invention preferably satisfies the following conditional expressions.
(10) S0*HG1*β/h≧21.0
however,
S0: Distance from the lens surface closest to the object side of the rear conversion lens to the imaging plane of the main lens (the direction from the object side to the image side is positive.)
HG1: effective ray height β on the lens surface closest to the object side of the rear conversion lens: magnification h of the rear conversion lens: maximum image height

Conditional expression (10) is a conditional expression for making the rear conversion lens of the present invention applicable even when the distance from the exit pupil position of the main lens to the imaging point is long. In a mirrorless camera system with a short flange focal distance, since the rear conversion lens is placed at a position close to the image forming point of the main lens, peripheral rays of the main lens are likely to be vignetted on the rear conversion lens side. In order to be applicable to the main lens having a long distance from the exit pupil position to the imaging point, it is important to appropriately set the position of the lens surface closest to the object side of the rear conversion lens and the effective ray height.

Exceeding the lower limit of conditional expression (10), the distance from the image plane of the main lens to the lens surface closest to the object side of the rear conversion lens becomes short, or the lens surface closest to the object side of the rear conversion lens becomes effective When the ray height becomes small, it becomes difficult to apply to a main lens having a long distance from the exit pupil position to the imaging point.

By limiting the lower limit of conditional expression (10) to 22.0, the above effect can be more reliably obtained.

Furthermore, the rear conversion lens of the present invention preferably satisfies the following conditional expressions.
(11) 1.85≤β≤2.15
however,
β: magnification of the rear conversion lens

Conditional expression (11) defines the magnification of the rear conversion lens.

If the lower limit of conditional expression (11) is exceeded, a sufficient magnification cannot be secured for the rear conversion lens. On the other hand, when the upper limit of conditional expression (11) is exceeded, the negative refractive power of the rear conversion lens becomes strong, making it difficult to correct various aberrations.

By restricting the lower limit to 1.90 and the upper limit to 2.10 for conditional expression (11), the above effects can be more reliably achieved.

Further, in the rear conversion lens of the present invention, the first lens group is composed of a set of three cemented lenses in which a negative lens, a positive lens, and a negative lens are cemented in order from the object side, and the second lens group is composed from the object side. It is desirable that the third lens group consists of a set of cemented lenses in which a negative lens and a positive lens are cemented in order, and that the third lens group consists of a set of cemented lenses in which a positive lens and a negative lens are cemented in order from the object side. .

By using a three-element cemented lens consisting of a negative lens, a positive lens, and a negative lens, it is possible to effectively correct spherical aberration and axial chromatic aberration while suppressing performance deterioration due to manufacturing errors such as lens spacing and eccentricity. becomes easier.

By using a cemented lens consisting of a negative lens and a positive lens in the second lens group, longitudinal chromatic aberration and chromatic aberration of magnification generated in the second lens group are reduced, and good chromatic aberration correction is facilitated throughout the rear conversion lens system. become.

By using a cemented lens consisting of a positive lens and a negative lens in the third lens group, it is possible to reduce longitudinal chromatic aberration and lateral chromatic aberration that occur in the third lens group, and facilitate good chromatic aberration correction in the entire rear conversion lens system. become.

Specific numerical values of each example of the rear conversion lens of the present invention described above are 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 each surface, and nd is for the d line (wavelength λ = 587.56 nm). The index of refraction, vd is the Abbe's number for the d-line, and the effective ray height is the height of the ray with the highest ray height on each surface.

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

[Aspheric surface data] shows each coefficient value that gives the aspheric shape of the lens surface marked with * in [Surface data]. As for the shape of the aspherical surface, y is the displacement in the direction orthogonal to the optical axis, z is the displacement (sag amount) in the optical axis direction from the intersection of the aspherical surface and the optical axis, and K, 4, 6, 8 is the conic coefficient. Let A4, A6, A8, and A10 be the 10th-order aspherical coefficients, respectively, and the coordinates of the aspherical surface are expressed by the following equations.

[Various data] shows values when the shooting distance is infinity (INF).

[Variable distance data] indicates values of variable distance and BF (back focus) at an infinite photographing distance (INF). Also, d1 is the distance between the surface of the main lens closest to the image side and the surface of the rear conversion lens closest to the object side.

[Lens group data] indicates the number of the surface closest to the object side constituting each lens group and the combined focal length of the entire group.

In addition, in all the following specification values, millimeters (mm) are used for the focal length f, radius of curvature r, distance between lens surfaces d, and other lengths unless otherwise specified. Since equivalent optical performance can be obtained in proportional enlargement and proportional reduction in , the invention is not limited to this.

1 and 4, S is an aperture stop, I is an image plane, F is a filter, and a dashed line passing through the center is an optical axis.

Next, a lens configuration of an example of the rear conversion lens of the present invention will be described.
In the following description, the lens configuration will be described in order from the object side to the image side.
(main lens)
FIG. 1 is a lens configuration diagram of a main lens to which the rear conversion lens of the present invention is attached.
However, the main lens is not limited to this. FIG. 4 shows a lens configuration diagram when the rear conversion lens of Example 1 is attached to the main lens.

The main lenses are, in order from the object side, a biconvex lens L1, a positive meniscus lens L2 with a convex surface facing the object side, a biconcave lens L3, a negative meniscus lens L4 with a convex surface facing the object side, and a convex surface facing the object side. a cemented lens composed of a positive meniscus lens L5, a cemented lens composed of a negative meniscus lens L6 having a convex surface facing the object side and a positive meniscus lens L7 having a convex surface facing the object side, an aperture stop, and a convex surface facing the object side. A cemented lens consisting of a negative meniscus lens L8 and a biconvex lens L9, and a cemented lens consisting of a biconcave lens L10, a biconvex lens L11, and a negative meniscus lens L12 having a convex surface facing the image side.

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 Effective ray height Object surface ∞ (d0)
1 111.9173 20.8268 1.43700 95.10 52.60
2 -495.5275 2.0000 51.77
3 113.6922 14.6266 1.43700 95.10 47.32
4 1558.7754 5.4143 45.61
5 -555.2988 4.0000 1.74330 49.22 44.09
6 359.9722 12.0000 42.21
7 87.7955 2.5000 1.78590 43.93 36.69
8 46.7063 16.2148 1.55032 75.50 33.46
9 137.9693 37.1684 31.75
10 822.2693 1.5000 1.83400 37.34 20.80
11 42.0060 5.4599 1.84666 23.78 19.72
12 76.3607 30.7194 19.20
13 (Aperture) ∞ 16.0306 16.25
14 94.7760 1.0000 2.00100 29.13 15.50
15 61.3988 5.7225 1.62004 36.30 15.48
16 -90.9221 22.2167 15.60
17 -63.4368 1.0000 1.59282 68.62 14.96
18 33.4595 10.0000 1.61340 44.27 15.43
19 -56.0440 1.0000 1.84666 23.78 15.68
20-943.8831 (BF) 15.97
Image plane ∞

[Various data]
INF
Focal length 290.00
F number 2.91
Full angle of view 2ω 8.38
Image height Y 21.63
Lens length 245.40

[Variable interval data]
INF
d0 ∞
BF 36.0000

FIG. 5 is a lens configuration diagram of the rear conversion lens of Example 1 of the present invention.
The rear conversion lens of Example 1 comprises, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a positive refractive power. is composed of a fourth lens group G4.

The first lens group is composed of a cemented lens composed of three lenses: a negative meniscus lens L1 having a convex surface facing the object side, a biconvex lens L2, and a negative meniscus lens L3 having a convex surface facing the image side. The second lens group is composed of a cemented lens composed of a biconcave lens L4 and a positive meniscus lens L5 having a convex surface facing the object side. The third lens group is composed of a cemented lens composed of a biconvex lens L6 and a biconcave lens L7. The fourth lens group is composed of a positive meniscus lens L8 having a convex surface facing the image side.

Next, the 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 Effective ray height
1 ∞ (d1)
2 77.6679 0.9000 2.00100 29.13 8.75
3 18.2216 6.5654 1.72825 28.32 8.69
4 -27.5847 0.9000 1.61997 63.88 8.85
5 -49.4085 2.8454 8.92
6 -41.2287 0.9000 1.88100 40.14 8.78
7 18.2640 3.5266 1.72825 28.32 9.10
8 40.4824 0.1500 9.41
9 28.0116 7.7516 1.59270 35.45 9.79
10 -26.1109 0.9000 2.05090 26.94 10.22
11 252.3233 13.3076 10.79
12 -44.8273 7.3681 1.51742 52.15 15.41
13 -24.5595 (BF) 16.84
Image plane ∞

[Various data]
INF
Focal length 581.99
F number 5.83
Full angle of view 2ω 4.21
Image height Y 21.63
Lens length 277.49

[Variable interval data]
INF
d1 5.1499
BF 17.8254


[Lens group data]
Group Starting surface Focal length
G1 2 68.99
G2 6 -20.37
G3 9 590.96
G4 12 93.40

FIG. 8 is a lens configuration diagram of a rear conversion lens according to Example 2 of the present invention.
The rear conversion lens of Example 2 comprises, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a positive refractive power. is composed of a fourth lens group G4.

The first lens group is composed of a cemented lens composed of three lenses: a negative meniscus lens L1 having a convex surface facing the object side, a biconvex lens L2, and a negative meniscus lens L3 having a convex surface facing the image side. The second lens group is composed of a cemented lens composed of a biconcave lens L4 and a positive meniscus lens L5 having a convex surface facing the object side. The third lens group is composed of a cemented lens composed of a biconvex lens L6 and a biconcave lens L7. The fourth lens group is composed of a positive meniscus lens L8 having a convex surface facing the image side.

Next, the 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 Effective ray height
1 ∞ (d1)
2 66.2995 0.9000 2.00100 29.13 8.75
3 16.4056 7.1760 1.72825 28.32 8.66
4 -27.7345 0.9000 1.61997 63.88 8.87
5 -58.0857 3.2163 8.94
6 -43.7911 0.9000 1.88100 40.14 8.87
7 18.0296 3.2214 1.72825 28.32 9.23
8 32.1134 0.1500 9.55
9 26.8903 8.2359 1.59270 35.45 9.91
10 -27.1593 0.9000 2.05090 26.94 10.54
11 244.8695 10.5759 11.22
12 -48.8261 9.1422 1.51742 52.15 15.39
13 -23.0000 (BF) 17.19
Image plane ∞

[Various data]
INF
Focal length 577.08
F number 5.78
Full angle of view 2ω 4.25
Image height Y 21.63
Lens length 276.46

[Variable interval data]
INF
d1 6.2634
BF 15.4787

[Lens group data]
Group Starting surface Focal length
G1 2 76.13
G2 6 -18.95
G3 9 302.62
G4 12 74.99

FIG. 11 is a lens configuration diagram of a rear conversion lens according to Example 3 of the present invention.
The rear conversion lens of Example 3 comprises, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with negative refractive power, and a positive refractive power. is composed of a fourth lens group G4.

The first lens group is composed of a cemented lens composed of three lenses: a negative meniscus lens L1 having a convex surface facing the object side, a biconvex lens L2, and a negative meniscus lens L3 having a convex surface facing the image side. The second lens group is composed of a cemented lens composed of a biconcave lens L4 and a positive meniscus lens L5 having a convex surface facing the object side. The third lens group is composed of a cemented lens composed of a biconvex lens L6 and a biconcave lens L7. The fourth lens group is composed of a positive meniscus lens L8 having a convex surface facing the image side.

Next, the 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 Effective ray height
1 ∞ (d1)
2 80.3158 0.9000 2.00100 29.13 8.75
3 19.3246 6.5616 1.72825 28.32 8.70
4 -27.3969 0.9000 1.61997 63.88 8.88
5 -52.0568 3.2474 8.95
6 -39.2284 0.9000 1.88100 40.14 8.82
7 18.6096 3.7769 1.72825 28.32 9.19
8 5.1241 0.1500 9.54
9 30.2666 8.7847 1.59270 35.45 9.92
10 -21.7674 0.9000 2.05090 26.94 10.46
11 153.2441 10.1347 11.31
12 -77.4957 10.5318 1.54814 45.82 16.08
13 -24.5879 (BF) 18.02
Image plane ∞

[Various data]
INF
Focal length 574.77
F number 5.76
Full angle of view 2ω 4.28
Image height Y 21.63
Lens length 276.30

[Variable interval data]
INF
d1 6.5664
BF 13.5493

[Lens group data]
Group Starting surface Focal length
G1 2 70.03
G2 6 -20.77
G3 9 -188.40
G4 12 61.38

FIG. 14 is a lens configuration diagram of a rear conversion lens of Example 4 of the present invention.
The rear conversion lens of Example 4 comprises, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a positive refractive power. is composed of a fourth lens group G4.

The first lens group is composed of a cemented lens composed of three lenses: a negative meniscus lens L1 having a convex surface facing the object side, a biconvex lens L2, and a negative meniscus lens L3 having a convex surface facing the image side. The image-side surface of the negative meniscus lens L3 has a predetermined aspheric shape. The second lens group is composed of a cemented lens composed of a biconcave lens L4 and a positive meniscus lens L5 having a convex surface facing the object side. The third lens group is composed of a cemented lens composed of a biconvex lens L6 and a negative meniscus lens L7 having a convex surface facing the image side. The fourth lens group is composed of a positive meniscus lens L8 having a convex surface facing the image side.

Next, the 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 Effective ray height
1 ∞ (d1)
2 46.7865 0.9000 2.00100 29.13 8.75
3 14.6938 7.3405 1.72825 28.32 8.59
4 -34.5768 0.9000 1.59201 67.02 8.75
5* -138.5516 1.8124 8.79
6 -64.1507 0.9000 1.88100 40.14 8.77
7 16.0395 3.6684 1.72825 28.32 9.01
8 28.5139 0.1500 9.32
9 24.3004 10.9546 1.59270 35.45 9.68
10 -18.0000 0.9000 2.05090 26.94 10.39
11 -306.2165 11.8059 11.37
12 -34.1272 7.3374 1.61340 44.27 15.54
13 -22.8483 (BF) 17.20
Image plane ∞

[Aspheric data]
5 sides
K 0.0000
A4-1.2357E-05
A6 7.7100E-09
A8-2.2311E-10
A10 0.0000

[Various data]
INF
Focal length 576.51
F number 5.78
Full angle of view 2ω 4.31
Image height Y 21.63
Lens length 275.62

[Variable interval data]
INF
d1 6.0060
BF 13.5471

[Lens group data]
Group Starting surface Focal length
G1 2 90.71
G2 6 -19.88
G3 9 165.09
G4 12 90.36

Also, a list of corresponding values of conditional expressions in each of these embodiments is shown.

[Value corresponding to conditional expression]
Conditional expression/Example ex1 ex2 ex3 ex4
(1) 0.40≤BF/h≤1.10 0.82 0.72 0.63 0.63
(2) 0.80≦(L-PPO)/L≦1.70 1.11 1.21 1.37 1.09
(3) -1.00≤(L+PPI)/L≤0.20 -0.19 -0.39 -0.69 -0.16
(4) 0.10≤f123/f≤0.60 0.42 0.34 0.26 0.41
(5) -0.30≤f2/f3≤0.30 -0.03 -0.06 0.11 -0.12
(6) 1.97≦nd3n 2.05 2.05 2.05 2.05
(7) See below 0.35 0.29 0.22 0.37
(8) 0.15≤RG4rear/f≤0.50 0.34 0.29 0.26 0.33
(9) See below -3.42 -2.78 -1.93 -5.05
(10) 21.0≤S0*HG1*β/h 25.05 23.94 23.60 24.12
(11) 1.85≤β≤2.15 2.01 1.99 1.98 1.99
* Conditional expression (7) 0.10≦(D34-PPI123+PPO4)/(-f)
* Conditional expression (9) -8.00≤(RG4rear+RG4front)/(RG4rear-RG4front)≤-1.20

ML Main lens RCL Rear conversion lens G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group S Aperture diaphragm I Image plane

Claims (7)

A rear conversion lens that is detachably mounted on the image side of a main lens and expands its focal length,
From the object side, the first lens group having positive refractive power, the second lens group having negative refractive power, the third lens group having positive or negative refractive power, and the fourth lens group having positive refractive power. consists of
each lens group consists of one lens or a set of cemented lenses,
The third lens group has one negative lens,
A rear conversion lens that satisfies the following conditional expressions.
(1) 0.40≤BF/h≤1.10
(2) 0.80≦(L-PPO)/L≦1.70
(3) -1.00 ≤ (L + PPI) / L ≤ 0.20
(4) 0.10≤f123/f≤0.60
(6) nd3n≧1.97
however,
BF: back focus with the rear conversion lens attached to the main lens h: maximum image height L: distance from the lens surface closest to the object side of the rear conversion lens to the lens surface closest to the image side PPO: the rear Distance from the most object-side lens surface of the conversion lens to the object-side principal point of the rear conversion lens (the direction from the object side to the image side is positive.)
PPI: Distance from the most image side lens surface of the rear conversion lens to the image side principal point of the rear conversion lens (the direction from the object side to the image side is positive.)
f123: combined focal length from the first lens group to the third lens group f: focal length of the entire rear conversion lens system
nd3n: refractive index for the d-line of the negative lens included in the third lens group

2. The rear conversion lens according to claim 1, which satisfies the following conditional expression.
(5) -0.30≤f2/f3≤0.30
however,
f2: focal length of the second lens group f3: focal length of the third lens group

3. The rear conversion lens according to claim 1, wherein the following conditional expression is satisfied.
(7) (D34-PPI123+PPO4)/(-f)≧0.100
however,
D34: Air gap between the third lens group and the fourth lens group PPI123: Image of the combined system of the first lens group to the third lens group from the lens surface closest to the image side of the third lens group Distance to the side principal point (The direction from the object side to the image side is positive.)
PPO4: Distance from the most object-side lens surface of the fourth lens group to the object-side principal point of the fourth lens group (the direction from the object side to the image side is positive.)
f: focal length of the entire rear conversion lens system
The fourth lens group consists of a single positive meniscus lens with a convex surface facing the image side,
4. The rear conversion lens according to claim 1, wherein the following conditional expression is satisfied.
(8) 0.15≦RG4rear/f≦0.50
(9) -8.00 ≤ (RG4 rear + RG4 front) / (RG4 rear - RG4 front) ≤ -1.20
however,
RG4rear: radius of curvature of the lens surface of the fourth lens group closest to the image side RG4front: radius of curvature of the lens surface closest to the object side of the fourth lens group f: focal length of the entire rear conversion lens system 5. The rear conversion lens according to claim 1, wherein the following conditional expression is satisfied.
(10) S0*HG1*β/h≧21.0
however,
S0: Distance from the lens surface closest to the object side of the rear conversion lens to the imaging plane of the main lens (the direction from the object side to the image side is positive.)
HG1: effective ray height β on the lens surface closest to the object side of the rear conversion lens: magnification h of the rear conversion lens: maximum image height 6. The rear conversion lens according to claim 1, wherein the following conditional expression is satisfied.
(11) 1.85≤β≤2.15
however,
β: magnification of the rear conversion lens
the first lens group consists of a set of three cemented lenses formed by cementing a negative lens, a positive lens, and a negative lens in order from the object side;
the second lens group comprises a cemented lens formed by cementing a negative lens and a positive lens in order from the object side;
7. The rear conversion lens according to any one of claims 1 to 6, wherein said third lens group comprises a cemented lens formed by cementing a positive lens and a negative lens in order from the object side.

Images