JP6123281B2 - Short-range correction lens system - Google Patents

Description

  The present invention relates to a short distance correction lens system suitable for use in a medium format single-lens reflex camera capable of photographing from infinity to a short distance.

  In a general photographing lens system, the photographing distance as a design standard is set to infinity or a low magnification of 0.1 times or less (0 to −0.1 times). In such a lens system, in order to photograph a short-distance object with a higher photographing magnification (for example, −0.5 times or more), if focusing is performed by the entire extension in which the entire lens system is extended to the object side, aberration fluctuations occur. The optical performance will deteriorate due to the increase. Therefore, in order to enable shooting of objects at shooting distances ranging from infinity to short distance, shooting using a floating mechanism that suppresses aberration fluctuations due to focusing by moving multiple lens groups independently at different ratios A lens system has been proposed (Patent Documents 1-6).

  The taking lens system of Patent Documents 1-3 is for a medium format single-lens reflex camera having a larger screen size than a 35 mm single-lens reflex camera. However, the photographic lens system of Patent Documents 1-3 has a relatively narrow angle of view that is about the angle of view of a medium telephoto lens, and from the viewpoint of securing light quantity and correcting aberrations, the angle of view of a standard lens (standard image). It cannot be applied to a photographic lens system having a wider angle of view.

  On the other hand, the photographing lens system of Patent Literature 4-6 has a wider angle of view than Patent Literatures 1-3, which are about the standard angle of view. However, since the photographic lens system of Patent Document 4-6 is optimized for the screen size of a 35 mm single-lens reflex camera, it cannot be applied to a medium-format single-lens reflex camera having a large screen size.

  In a single-lens reflex camera system, there is a demand for making the back focus sufficiently long in order to avoid a mirror located between the final lens (most image side lens) and the image plane coming into contact with the final lens. In particular, a medium-format single-lens reflex camera having a screen size larger than that of a 35 mm single-lens reflex camera is required to ensure a longer back focus with respect to the focal length. However, in order to apply the photographic lens system of Patent Documents 4-6 to a medium format single-lens reflex camera with the same angle of view, the standard angle of view can be realized simply by enlarging (scaling) the entire lens system. Is difficult and leads to an increase in the overall length. That is, if the photographic lens system of Patent Document 4-6 is scaled to a size for a medium format single-lens reflex camera without changing the angle of view, the back focus will be insufficient, and if the scale is scaled to a size that can ensure sufficient back focus, the focal length will be increased. Long (the angle of view is narrow).

JP 11-231210 A JP 2003-185916 A JP 2003-279849 A JP-A-6-130291 JP 2008-257088 A JP 2004-61680 A

  The present invention has been completed based on the above awareness of the problem. Particularly in a short-range correction lens system used in a medium-format single-lens reflex camera, the field angle is relatively wide, about 42 to 43 degrees, and the medium-format single-lens reflex camera is An object of the present invention is to obtain a short-distance correction lens system that can secure the back focus necessary for the camera and can correct aberrations well over a wide photographing region from infinity to short distance.

The short-distance correction lens system of the present invention includes a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side, and performs focusing from an infinite object to a short-distance object. In the short-distance correction lens system in which at least the first lens unit moves toward the object side, the first lens unit includes, in order from the object side, a first lens unit having a positive refractive power, a first lens unit having a negative refractive power, The aperture stop and the first c lens group having a positive refractive power are composed of a cemented lens of a negative lens concave on the image side and a positive lens concave on the image side, which are located in order from the object side . The two lens group includes , in order from the object side, a negative lens that is concave on the image side, a positive lens, and a negative lens that is concave on the object side, and satisfies the following conditional expression (12) .
_{(12) 0 <νd 1bn -νd} 1bp <20
However,
νd _1bn : Abbe number for the d-line of the negative lens in the 1b lens group,
νd _1bp : Abbe number for the d-line of the positive lens in the 1b lens group,
It is.

It is preferable that the short distance correction lens system of the present invention satisfies the following conditional expression (1).
(1) −1.6 <(R _21i + R _21O ) / (R _21i −R _21O ) <− 0.6
However,
R _21i : radius of curvature of the image side surface of the negative lens concave to the image side in the second lens group,
R _21O : the radius of curvature of the object side surface of the negative lens concave to the image side in the second lens group,
It is.

The short-distance correction lens system of the present invention preferably satisfies the following conditional expression (2).
(2) 0.1 <R _23O / f ₂ <2.0
However,
R _23O : radius of curvature of the object side surface of the negative lens concave on the object side in the second lens group,
f ₂ : focal length of the second lens group,
It is.

It is preferable that the short distance correcting lens system according to the present invention satisfies the following conditional expression (3).
(3) 0.2 <f ₂₁ / f ₂ <0.7
However,
f ₂₁ : the focal length of the negative lens concave on the image side in the second lens group,
f ₂ : focal length of the second lens group,
It is.

The short-distance correction lens system of the present invention preferably satisfies the following conditional expression (4).
(4) 0.2 <f ₂₃ / f ₂ <0.9
However,
f ₂₃ : focal length of negative lens concave on the object side in the second lens group,
f ₂ : focal length of the second lens group,
It is.

It is preferable that the short distance correcting lens system according to the present invention satisfies the following conditional expression (5).
(5) νd ₂₃ <60
However,
νd ₂₃ : Abbe number with respect to the d-line of the negative lens concave on the object side in the second lens group,
It is.

  The first lens group is preferably located closest to the object side and has a concave negative lens on the image side.

When a negative lens which is concave on the image side is disposed closest to the object side of the first lens group, it is preferable that the short distance correction lens system of the present invention satisfies the following conditional expressions (6) and (7).
(6) nd ₁₁ > 1.65
(7) νd ₁₁ > 40
However,
nd ₁₁ : refractive index with respect to d line of a negative lens which is concave on the image side located closest to the object side in the first lens group
νd ₁₁ : Abbe number for the d-line of the negative lens on the image side located closest to the object side in the first lens group,
It is.

In the short-distance correction lens system of the present invention, it is preferable that the first lens group has at least one positive lens and satisfies the following conditional expressions (8) and (9).
(8) nd _P1 > 1.7
(9) νd _P1 <60
However,
nd _P1 : refractive index with respect to d-line of at least one positive lens among at least one positive lens in the first lens group,
νd _P1 : Abbe number for the d-line of at least one positive lens among at least one positive lens in the first lens group,
It is.

In one aspect, the short distance correction lens system of the present invention is arranged such that the first lens group moves to the object side (draws out) during focusing from an object at infinity to a short distance object, and the second lens group. However, it moves to the object side by a different amount of movement from the first lens group (drawn out), and the following conditional expression (10) is satisfied.
(10) 0.1 <Δd2 / Δd1 <0.9
However,
Δd1: Amount of movement of the first lens unit during focusing from an object at infinity to a near object;
Δd2: the amount of movement of the second lens group during focusing from an infinitely distant object to a close object;
It is.

The short distance correcting lens system of the present invention preferably satisfies the following conditional expression (10 ′) within the conditional expression range of conditional expression (10).
(10 ′) 0.5 <Δd2 / Δd1 <0.9

  In another aspect of the short distance correction lens system of the present invention, the second lens group is fixed with respect to the image plane (does not move in the optical axis direction) during focusing from an object at infinity to a short distance object. .

It is preferable that the short distance correction lens system according to the present invention satisfies the following conditional expression (11).
(11) νd _1bn > 30
However,
νd _1bn : Abbe number for the d-line of the negative lens in the 1b lens group,
It is.

Short-range correction lens system of the present invention, among of the condition of the conditional expression (12), it is preferable to satisfy the following condition (12 ').
_{(12 ') 0 <νd 1bn} -νd 1bp <15

It is preferable that the short distance correction lens system of the present invention satisfies the following conditional expressions (13) and (14).
(13) nd _1bn <1.7
(14) nd _1bp > 1.8
However,
nd _1bn : refractive index with respect to d-line of the negative lens in the 1b lens group,
nd _1bp : refractive index of the positive lens in the 1b lens group with respect to d-line,
It is.

  According to the present invention, particularly in a short-distance correction lens system used in a medium format single-lens reflex camera, the angle of view is relatively wide as about 42 to 43 degrees, and the back focus necessary for the medium format single-lens reflex camera can be secured. A short-distance correction lens system that can satisfactorily correct aberrations over a wide imaging region up to a short distance can be obtained.

It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 1 of a short distance correction | amendment lens system . FIG. 2 is a diagram illustrating various aberrations in the configuration of FIG. 1. FIG. 2 is a lateral aberration diagram in the configuration of FIG. 1. It is a lens block diagram in the short distance photographing state of the same reference example 1 . FIG. 5 is a diagram illustrating various aberrations in the configuration of FIG. 4. FIG. 5 is a lateral aberration diagram in the configuration of FIG. 4. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 2 of a short distance correction lens system . FIG. 8 is a diagram illustrating various aberrations in the configuration of FIG. 7. FIG. 8 is a lateral aberration diagram in the configuration of FIG. 7. It is a lens block diagram in the short distance imaging | photography state of the same reference example 2 . FIG. 11 is a diagram illustrating various aberrations in the configuration of FIG. 10. FIG. 11 is a lateral aberration diagram in the configuration of FIG. 10. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 3 of a short distance correction lens system . FIG. 14 is a diagram illustrating various aberrations in the configuration of FIG. 13. FIG. 14 is a lateral aberration diagram in the configuration of FIG. 13. It is a lens block diagram in the short distance imaging | photography state of the same reference Example 3 . FIG. 17 is a diagram of various aberrations in the configuration of FIG. 16. FIG. 17 is a lateral aberration diagram in the configuration of FIG. 16. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 4 of a short distance correction lens system . FIG. 20 is a diagram illustrating various aberrations in the configuration in FIG. 19. FIG. 20 is a lateral aberration diagram in the configuration of FIG. 19. It is a lens block diagram in the short distance imaging | photography state of the same reference example 4 . FIG. 23 is a diagram of various aberrations in the configuration of FIG. 22. FIG. 23 is a lateral aberration diagram in the configuration of FIG. 22. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 5 of a short distance correction | amendment lens system . FIG. 26 is a diagram illustrating various aberrations in the configuration in FIG. 25. FIG. 26 is a lateral aberration diagram in the configuration of FIG. 25. It is a lens block diagram in the short distance imaging | photography state of the same reference Example 5 . FIG. 29 is a diagram of various aberrations in the configuration of FIG. 28. FIG. 29 is a lateral aberration diagram in the configuration of FIG. 28. It is a lens block diagram in the infinite point imaging | photography state of the reference Example 6 of a short distance correction | amendment lens system . FIG. 32 is a diagram of various aberrations in the configuration of FIG. 31. FIG. 32 is a lateral aberration diagram in the configuration of FIG. 31. It is a lens block diagram in the short distance imaging | photography state of the same reference example 6 . FIG. 35 is a diagram showing various aberrations in the configuration of FIG. 34. FIG. 35 is a lateral aberration diagram in the configuration of FIG. 34. It is a lens block diagram in the infinite point imaging | photography state of the reference Example 7 of a short distance correction | amendment lens system . FIG. 38 is a diagram of various aberrations in the configuration of FIG. 37. FIG. 38 is a lateral aberration diagram in the configuration of FIG. 37. It is a lens block diagram in the short distance imaging | photography state of the same reference example 7 . FIG. 41 is a diagram of various aberrations in the configuration of FIG. 40. FIG. 41 is a lateral aberration diagram in the configuration of FIG. 40. It is a lens block diagram in the infinite point imaging | photography state of the reference Example 8 of a short distance correction lens system . FIG. 44 is a diagram of various aberrations in the configuration of FIG. 43. FIG. 44 is a lateral aberration diagram in the configuration of FIG. 43. It is a lens block diagram in the short distance imaging | photography state of the same reference example 8 . FIG. 47 is a diagram of various aberrations in the configuration of FIG. 46. FIG. 47 is a transverse aberration diagram for the configuration in FIG. 46. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 9 of a short distance correction | amendment lens system . FIG. 50 is a diagram of various aberrations in the configuration of FIG. 49. FIG. 50 is a transverse aberration diagram for the structure in FIG. 49. It is a lens block diagram in the short distance photographing state of the same reference example 9 . FIG. 53 is a diagram of various aberrations in the configuration of FIG. 52. FIG. 53 is a lateral aberration diagram in the configuration of FIG. 52. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 10 of a short distance correction | amendment lens system . FIG. 56 is a diagram of various aberrations in the configuration of FIG. 55. FIG. 56 is a transverse aberration diagram for the configuration in FIG. 55. It is a lens block diagram in the short distance imaging | photography state of the same reference example 10 . FIG. 59 is a diagram of various aberrations in the configuration of FIG. 58. FIG. 59 is a transverse aberration diagram for the structure of FIG. 58. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 11 of a short distance correction | amendment lens system . FIG. 62 is a diagram of various aberrations in the configuration of FIG. 61. FIG. 62 is a transverse aberration diagram for the structure in FIG. 61. It is a lens block diagram in the short distance imaging | photography state of the same reference example 11 . FIG. 65 is a diagram of various aberrations in the configuration of FIG. 64. FIG. 65 is a transverse aberration diagram for the structure in FIG. 64. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 12 of a short distance correction | amendment lens system . FIG. 68 is a diagram of various aberrations in the configuration of FIG. 67. FIG. 68 is a transverse aberration diagram for the structure in FIG. 67. It is a lens block diagram in the short distance imaging | photography state of the reference example 12 . FIG. 71 is a diagram of various aberrations in the configuration of FIG. 70. FIG. 71 is a transverse aberration diagram for the structure in FIG. 70. It is a lens block diagram in the infinite distance imaging | photography state of the reference Example 13 of a short distance correction lens system . FIG. 74 is a diagram of various aberrations in the configuration of FIG. 73. FIG. 74 is a transverse aberration diagram for the structure in FIG. 73. It is a lens block diagram in the short distance imaging | photography state of the reference Example 13 . FIG. 77 is a diagram of various aberrations in the configuration of FIG. 76. FIG. 77 is a transverse aberration diagram for the configuration in FIG. 76. It is a lens block diagram in the infinite distance imaging | photography state of Numerical Example 1 of the short distance correction lens system by this invention. FIG. 80 is a diagram of various aberrations in the configuration of FIG. 79. FIG. 80 is a transverse aberration diagram for the structure in FIG. 79. It is a lens block diagram in the short distance imaging | photography state of the same numerical value Example 1. FIG. FIG. 83 is a diagram of various aberrations in the configuration of FIG. 82. FIG. 83 is a transverse aberration diagram for the structure of FIG. 82. It is a lens block diagram in the infinite distance imaging | photography state of Numerical Example 2 of the short distance correction lens system by this invention. FIG. 88 is a diagram of various aberrations in the configuration in FIG. 85. FIG. 88 is a transverse aberration diagram for the structure in FIG. 85. It is a lens block diagram in the short distance photographing state of the numerical example 2 ; FIG. 89 is a diagram of various aberrations in the configuration of FIG. 88. FIG. 89 is a transverse aberration diagram for the structure in FIG. 88. It is a lens block diagram in the infinite point imaging | photography state of Numerical Example 3 of the short distance correction lens system by this invention. FIG. 92 is a diagram showing aberrations in the configuration of FIG. 91. FIG. 92 is a transverse aberration diagram for the structure in FIG. 91. It is a lens block diagram in the short distance imaging | photography state of the same numerical example 3. FIG. FIG. 95 is a diagram of various aberrations in the configuration of FIG. 94. FIG. 95 is a transverse aberration diagram for the structure in FIG. 94. It is a simple movement figure which shows the 1st movement locus | trajectory in the case of focusing from an infinite object to a short distance object of the short distance correction lens system by this invention. It is a simple movement figure which shows the 2nd movement locus | trajectory in the case of focusing from an infinite distance object to a short distance object of the short distance correction lens system by this invention.

As shown in the simplified movement diagrams of FIGS. 97 and 98, the short-distance correction lens system is a first lens group having a positive refractive power in order from the object side through Reference Example 1-13 and Numerical Example 1-3 . G1 and a second lens group G2 having a negative refractive power. I is the image plane.

In the short distance correction lens system, when focusing from an object at infinity to a short distance object through Reference Example 1-13 and Numerical Example 1-3 , at least the first lens group G1 is spaced from the second lens group G2. Move to the object side while changing.

In the reference example 1-9 and the numerical value example 1-3 , the short-distance correction lens system includes the first lens group G1 during focusing from an object at infinity to a short-distance object, as shown in the simplified movement diagram of FIG. And the second lens group G2 move to the object side with different movement amounts (feeding amounts). The moving amount (feeding amount) of the first lens group G1 is larger than the moving amount (feeding amount) of the second lens group G2.

In Reference Example 10-13 , as shown in the simplified movement diagram of FIG. 98 , the short-distance correction lens system moves the first lens group G1 to the object side during focusing from an infinite object to a short-distance object ( The second lens group G2 is fixed with respect to the image plane I (does not move in the optical axis direction).

In Reference Example 1-13 , the first lens group G1 includes, in order from the object side, a negative lens (a negative lens concave on the image side) 11, a positive lens 12, a positive lens 13, a negative lens 14, an aperture stop S, an object It consists of a cemented lens of a negative lens 15 and a positive lens 16, and a positive lens 17 that are positioned in this order from the side. The positive lens 17 has an aspheric image side surface.

In Numerical Example 1-3 , the first lens group G1 includes, in order from the object side, a first-a lens group G1a having a positive refractive power, a first-b lens group G1b having a negative refractive power, an aperture stop S, and a positive refraction. It consists of a first-c lens group G1c.
The first-a lens group G1a includes a negative lens 11 ′, a positive lens 12 ′, and a positive lens 13 ′ in order from the object side. In the numerical examples 1 and 2 , the positive lens 12 ′ is a spherical lens, and in the numerical example 3 , the object side surface is an aspherical surface.
The 1b lens group G1b is composed of a cemented lens of a negative lens (negative lens concave on the image side) 14 ′ and a positive lens (positive lens concave on the image side) 15 ′ positioned in order from the object side.
The first c lens group G1c includes, in order from the object side, a cemented lens of a negative lens 16 ′ and a positive lens 17 ′ and a positive lens 18 ′ that are sequentially positioned from the object side. The positive lens 18 ′ has an aspheric image side surface throughout Numerical Example 1-3 .

The second lens group G2 includes a negative lens (a negative lens concave on the image side) 21, a positive lens 22, and a negative lens (object side) in order from the object side through Reference Example 1-13 and Numerical Example 1-3. Negative lens 23).

In Reference Example 1-9 and Numerical Example 1-3 , a floating focus that moves the first lens group G1 and the second lens group G2 to the object side with different amounts of movement during focusing from an infinitely distant object to a close object. In this way, off-axis aberrations such as field curvature and distortion are particularly well corrected when photographing a short distance object. Further, by moving the first lens group G1 to the object side, the storage length can be shortened and the portability can be improved.

Also, as in Reference Example 10-13 , when focusing from an infinitely distant object to a close object, the first lens group G1 is moved to the object side, and the second lens group G2 is fixed with respect to the image plane I. Thus, the focus mechanism system can be simplified. Further, the decentration sensitivity of the second lens group G2 can be kept small, and the practical optical performance can be maintained at an excellent level.

In the short distance correction lens system, through Reference Example 1-13 and Numerical Example 1-3 , the second lens group G2 is arranged in order from the object side, with a negative lens (negative lens concave on the image side) 21, and a positive lens 22. , And a negative lens (negative lens concave on the object side) 23.

  By configuring the two lenses on the object side of the second lens group G2 in the order of the negative lens (negative lens concave on the image side) 21 and the positive lens 22, spherical aberration and coma can be favorably corrected. it can.

  By disposing a negative lens (concave negative lens on the image side) 21 closest to the object side of the second lens group G2 (that is, the position closest to the aperture stop S), off-axis aberrations such as field curvature and distortion aberration can be obtained. A long back focus can be secured while minimizing the influence.

  If the final lens (lens closest to the image side) of the second lens group G2 is a positive lens, the lens diameter increases, which is not preferable for a single-lens reflex camera system in which the effective diameter is limited by the mount. Therefore, in the present embodiment, the final lens (lens closest to the image side) of the second lens group G2 is a negative lens (negative lens concave on the object side) 23, thereby reducing the lens diameter of the second lens group G2. ing.

  By making the negative lens 21 closest to the object side of the second lens group G2 concave on the image side, making the negative lens 23 closest to the image side concave on the object side, and making the shapes of the negative lenses 21 and 23 symmetrical, It is possible to satisfactorily correct field curvature and distortion. Further, the positive lens 22 positioned between the negative lenses 21 and 23 is formed into a biconvex shape along the concave surface on the image side of the negative lens 21 and the concave surface on the object side of the negative lens 23, so that spherical aberration is achieved. The occurrence of coma can be suppressed.

In Numerical Example 1-3 , the short distance correction lens system includes a first lens group G1, a first a lens group G1a having a positive refractive power, a first b lens group G1b having a negative refractive power, an aperture stop S, and a positive The first c lens group G1c having a refractive power of 5 mm is used. As a result, in the 1b lens group G1b, the off-axis light beam passes near the optical axis, so that aberration variation (particularly off-axis aberration variation such as curvature of field and lateral chromatic aberration) due to decentration error during manufacture is suppressed, and excellent optics. Performance can be obtained. Also, an image blur correction lens group (anti-vibration lens group) that corrects image blur by moving the first b lens group G1b positioned immediately before the aperture stop S in the direction orthogonal to the optical axis and changing the image formation position; You can also

  The 1b lens group G1b is composed of two lenses, a negative lens (a negative lens concave on the image side) 14 ′ and a cemented lens of a positive lens (positive lens concave on the image side) 15 ′ positioned in order from the object side. . As a result, aberration fluctuations due to decentration (particularly off-axis aberration fluctuations such as field curvature and lateral chromatic aberration) can be further reduced.

  By making the object-side surface of the first-b lens group G1b (negative lens 14 ′) concave, spherical aberration and coma can be favorably corrected. The cemented surface of the negative lens 14 ′ and the positive lens 15 ′ of the first-b lens group G1b is convex on the object side (the negative lens 14 ′ has a concave surface on the image side, and the positive lens 15 ′ has a convex surface on the object side. ), It is possible to suppress the occurrence of spherical aberration.

Conditional expression (1) defines the shape (shaping factor) of the most object side negative lens (negative lens concave on the image side) 21 in the second lens group G2. By satisfying conditional expression (1), it is possible to satisfactorily correct spherical aberration and curvature of field.
If the upper limit of conditional expression (1) is exceeded, spherical aberration and curvature of field become insufficiently corrected.
If the lower limit of conditional expression (1) is exceeded, spherical aberration and field curvature will be overcorrected.

Conditional expression (2) indicates that the radius of curvature of the object-side surface of the most image-side negative lens (negative lens concave on the object side) 23 in the second lens group G2 and the focal length of the second lens group G2 The ratio is specified. By satisfying conditional expression (2), it is possible to obtain good optical performance while suppressing the occurrence of coma, lateral chromatic aberration, and astigmatism.
If the upper limit of conditional expression (2) is exceeded, coma and lateral chromatic aberration will be undercorrected.
If the lower limit of conditional expression (2) is exceeded, astigmatism and chromatic coma aberration will occur greatly.

Conditional expression (3) defines the ratio between the focal length of the most object side negative lens (negative lens concave on the image side) 21 in the second lens group G2 and the focal length of the second lens group G2. Yes. By satisfying conditional expression (3), a long back focus can be secured and astigmatism, spherical aberration, and axial chromatic aberration can be corrected well.
When the upper limit of conditional expression (3) is exceeded, astigmatism becomes insufficiently corrected, and it becomes difficult to ensure the back focus.
If the lower limit of conditional expression (3) is exceeded, spherical aberration and axial chromatic aberration will be undercorrected.

Conditional expression (4) defines the ratio between the focal length of the most image side negative lens (negative lens concave on the object side) 23 in the second lens group G2 and the focal length of the second lens group G2. Yes. By satisfying conditional expression (4), it is possible to satisfactorily correct lateral chromatic aberration, spherical aberration, axial chromatic aberration, and field curvature.
If the upper limit of the conditional expression (4) is exceeded, the lateral chromatic aberration will be undercorrected, and the axial chromatic aberration at the time of shooting a short distance object will be overcorrected.
If the lower limit of conditional expression (4) is exceeded, spherical aberration, field curvature, and axial chromatic aberration will be undercorrected.

Conditional expression (5) defines the Abbe number for the d-line of the most image side negative lens (negative lens concave on the object side) 23 in the second lens group G2. By using a highly dispersed glass material that satisfies the conditional expression (5) for the negative lens 23, the lateral chromatic aberration can be corrected more effectively.
If the upper limit of conditional expression (5) is exceeded, lateral chromatic aberration will be undercorrected.

  As described above, the first lens group G1 includes the negative lens 11 that is located closest to the object side and that is concave on the image side. Conditional expression (6) and conditional expression (7) are defined based on this configuration. By disposing the negative lens 11 that is concave on the image side closest to the object side of the first lens group G1, it is possible to secure a large amount of light and ensure a wide angle of view without increasing the lens diameter. If the most object-side lens of the first lens group G1 is a negative lens convex to the image side, field curvature and distortion are greatly generated, which is not preferable.

Conditional expression (6) defines the refractive index with respect to the d-line of the negative lens 11 that is concave on the image side located closest to the object side in the first lens group G1. By satisfying conditional expression (6), it is possible to satisfactorily correct spherical aberration and coma.
If the lower limit of conditional expression (6) is exceeded, it will be difficult to suppress the occurrence of spherical aberration and coma.

Conditional expression (7) defines the Abbe number with respect to the d-line of the negative lens 11 that is concave on the image side located closest to the object side in the first lens group G1. By satisfying conditional expression (7), the lateral chromatic aberration can be satisfactorily corrected.
If the lower limit of conditional expression (7) is exceeded, the correction of lateral chromatic aberration will be insufficient.

  As described above, the first lens group G1 has four positive lenses (at least one positive lens) 12, 13, 16, and 17. Conditional expression (8) and conditional expression (9) are defined based on this configuration.

Conditional expression (8) defines the refractive index with respect to the d-line of at least one of the positive lenses 12, 13, 16, and 17 in the first lens group G1. By satisfying conditional expression (8), spherical aberration and coma can be corrected well.
If the lower limit of conditional expression (8) is exceeded, it will be difficult to suppress the occurrence of spherical aberration and coma.

Conditional expression (9) defines the Abbe number for the d-line of at least one of the positive lenses 12, 13, 16, and 17 in the first lens group G1. By satisfying conditional expression (9), the lateral chromatic aberration can be satisfactorily corrected.
If the upper limit of conditional expression (9) is exceeded, the correction of lateral chromatic aberration will be insufficient.

  In the present embodiment, the chromatic aberration of magnification is corrected more satisfactorily by setting the positive lens satisfying the conditional expressions (8) and (9) to the positive lens 12 located closest to the object side in the first lens group G1. Can do.

As described above, in Reference Example 1-9 , the first lens group G1 and the second lens group G2 are moved to the object side by different moving amounts (feeding amounts) during focusing from an infinitely distant object to a close object. (Feeding out).
Conditional expression (10) defines the ratio of the moving amounts (feeding amounts) of the first lens group G1 and the second lens group G2 during focusing from an infinitely distant object to a close object in this configuration. By satisfying conditional expression (10), the amount of movement of the entire lens system (feeding amount) accompanying focusing is set appropriately, and off-axis aberrations such as field curvature and distortion during close-up object photography are good. Can be corrected.
Exceeding the upper limit of conditional expression (10) is not practically preferable because the movement amount (feeding amount) of the entire lens system accompanying focusing increases. Further, due to the eccentricity caused by the tilting of the first lens group G1 and the second lens group G2 as the focus lens group, the image surface tilting is likely to occur.
If the lower limit of conditional expression (10) is exceeded, correction of off-axis aberrations such as field curvature and distortion during short-distance object shooting will be insufficient.

Conditional expression (11) indicates that, as in Numerical Example 1-3 , the first-b lens group G1b is composed of a negative lens (a negative lens concave on the image side) 14 ′ and a positive lens (on the image side) positioned in order from the object side. When the lens is composed of a cemented lens having a concave positive lens 15 ′, the Abbe number with respect to the d-line of the negative lens 14 ′ is defined. By satisfying conditional expression (11), it is possible to suppress the variation in lateral chromatic aberration when the 1b lens group G1b is decentered.
When the lower limit of conditional expression (11) is exceeded, correction of lateral chromatic aberration at the time of decentering of the first b lens group G1b becomes insufficient.

Conditional expression (12) indicates that the 1b lens group G1b is a cemented lens of a negative lens (a negative lens concave on the image side) 14 ′ and a positive lens (a positive lens concave on the image side) 15 ′ positioned in order from the object side. The difference between the Abbe number with respect to the d-line between the negative lens 14 ′ and the positive lens 15 ′ is defined. By satisfying conditional expression (12), it is possible to suppress the variation in lateral chromatic aberration when the 1b lens group G1b is decentered.
Since the 1b lens group G1b has a negative refractive power as a whole, in order to correct chromatic aberration in the 1b lens group G1b, a material having lower dispersion than the positive lens 15 ′ is used for the negative lens 14 ′. It is necessary to ensure an appropriate Abbe number difference satisfying the conditional expression (12) between the negative lens 14 ′ and the positive lens 15 ′.
If the upper limit of conditional expression (12) is exceeded, the lateral chromatic aberration at the time of decentering of the 1b lens group G1b will be overcorrected.
If the lower limit of conditional expression (12) is exceeded, correction of lateral chromatic aberration at the time of decentering of the first b lens group G1b will be insufficient.

Conditional expressions (13) and (14) indicate that the 1b lens group G1b includes a negative lens (a negative lens concave on the image side) 14 ′ and a positive lens (a positive lens concave on the image side) 15 positioned in order from the object side. The refractive index with respect to the d-line, which the negative lens 14 'and the positive lens 15' should satisfy when the lens is constituted by a cemented lens of ', is defined. When the conditional expressions (3) and (4) are satisfied, the Petzval sum is appropriate, and not only the non-eccentricity but also the curvature of field can be corrected well.
Even if the upper limit of conditional expression (3) is exceeded or the lower limit of conditional expression (4) is exceeded, correction of each field curvature becomes difficult.

[Reference Example 1-13 and Numerical Example 1-3]
Next, specific Reference Example 1-13 and Numerical Example 1-3 are shown. In the various aberration diagrams, lateral aberration diagrams and tables, d-line, g-line and C-line are aberrations for each wavelength, S is sagittal, M is meridional, FNO _. Is F-number, f is the focal length of the whole system, W Is the half field angle (°), Y is the image height, fB is the back focus, L is the total lens length, r is the radius of curvature, d is the lens thickness or lens spacing, N (d) is the refractive index with respect to the d line, and νd is d. Abbe number for the line, “Ea” means “× 10 ^−a ”. The unit of length is [mm]. The f-number, the image height, the back focus, the total lens length, and the lens interval d, the interval of which varies with focusing, are shown in the order of infinity shooting state-short-distance shooting state (shortest shooting state).
A rotationally symmetric aspherical surface is defined by
x = cy ² / [1+ [1- (1 + K) c ² y ² ] ^1/2 ] + A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰ + A12y ¹² ...
(Where c is the curvature (1 / r), y is the height from the optical axis, K is the conic coefficient, A4, A6, A8,... Are the aspheric coefficients of each order)

[Reference Example 1]
1 to 6 and Tables 1 to 3 show Reference Example 1 of a short-distance correction lens system . FIG. 1 is a lens configuration diagram in an infinite distance shooting state, FIG. 2 is a diagram of various aberrations thereof, FIG. 3 is a lateral aberration diagram thereof, FIG. 4 is a lens configuration diagram in a close-up shooting mode, and FIG. FIG. 6 is a lateral aberration diagram thereof. Table 1 shows surface data, Table 2 shows various data, and Table 3 shows aspherical data.

The short distance correction lens system of Reference Example 1 includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power.

  The first lens group G1 includes, in order from the object side, a negative meniscus lens that is convex on the object side (a negative lens concave on the image side) 11, a biconvex positive lens 12, a biconvex positive lens 13, a biconcave negative lens 14, and an aperture. It comprises a stop S, a cemented lens of a biconcave negative lens 15 and a biconvex positive lens 16 positioned in order from the object side, and a biconvex positive lens 17. The biconvex positive lens 17 has an aspheric image side surface.

  The second lens group G2 includes, in order from the object side, a biconcave negative lens (negative lens concave on the image side) 21, a biconvex positive lens 22, and a biconcave negative lens (negative lens concave on the object side) 23. .

  The first lens group G1 and the second lens group G2 move (draw out) to the object side with different movement amounts (feed-out amounts) when focusing from an object at infinity to an object at a short distance. The moving amount (feeding amount) of the first lens group G1 is larger than the moving amount (feeding amount) of the second lens group G2.

(Table 1)
Surface data surface number rd N (d) νd
1 1977.748 2.500 1.80610 40.7
2 47.374 11.870
3 64.269 7.090 1.80610 33.3
4 -893.056 3.580
5 66.415 10.000 1.49700 81.6
6 -121.009 10.330
7 -101.977 1.800 1.62004 36.3
8 206.839 3.670
9 stops ∞ 6.870
10 -32.907 2.000 1.67270 32.2
11 716.307 7.880 1.49700 81.6
12 -33.126 1.840
13 176.357 5.650 1.80139 45.5
14 * -98.056 d14
15 -602.490 1.650 1.51742 52.2
16 78.473 3.120
17 119.015 5.320 1.80450 39.6
18 -78.728 5.050
19 -61.010 1.650 1.59551 39.2
20 149.789-
* Is a rotationally symmetric aspherical surface.
(Table 2)
Various data
Infinity shooting state Short distance (-0.50 times) shooting state
FNO. 2.88 3.95
f 90.04
W 21.2
Y 34.85 34.85
fB 69.86 73.14
L 167.23 198.46
d14 5.500 33.457
(Table 3)
Aspheric data surface number K A4 A6
14 0.000 0.9099E-06 0.2694E-09

[Reference Example 2]
7 to 12 and Tables 4 to 6 show Reference Example 2 of the short distance correction lens system . FIG. 7 is a lens configuration diagram in the infinity shooting state, FIG. 8 is its aberration diagram, FIG. 9 is its lateral aberration diagram, FIG. 10 is a lens configuration diagram in the close-up shooting status, FIG. 11 is its aberration diagram, FIG. 12 is a lateral aberration diagram thereof. Table 4 shows surface data, Table 5 shows various data, and Table 6 shows aspherical data.

The lens configuration of the reference example 2 is the same as that of the reference example 1 except for the following points.
(1) The positive lens 12 of the first lens group G1 is a positive meniscus lens convex toward the object side.
(2) The negative lens (negative lens concave on the image side) 21 of the second lens group G2 is a negative meniscus lens convex on the object side.

(Table 4)
Surface data surface number rd N (d) νd
1 1977.151 2.500 1.74400 44.9
2 49.169 13.030
3 60.871 7.120 1.80450 39.6
4 1681.316 4.890
5 66.120 10.980 1.48749 70.4
6 -118.685 8.950
7 -67.315 1.800 1.56732 42.8
8 197.923 3.790
9 stops ∞ 6.540
10 -35.792 2.000 1.64769 33.8
11 1710.229 7.520 1.49700 81.6
12 -34.240 2.050
13 126.928 6.000 1.69350 53.2
14 * -112.336 d14
15 4344.585 1.650 1.54814 45.8
16 85.211 2.940
17 116.847 3.620 1.83400 37.3
18 -103.779 7.170
19 -73.685 1.650 1.62004 36.3
20 153.595-
* Is a rotationally symmetric aspherical surface.
(Table 5)
Various data
Infinity shooting state Short-distance (-0.75x) shooting state
FNO. 2.88 4.67
f 90.52
W 21.2
Y 34.85 34.85
fB 67.40 78.52
L 167.10 221.36
d14 5.500 48.640
(Table 6)
Aspheric data surface number K A4 A6
14 0.000 0.1091E-05 0.3256E-09

[Reference Example 3]
13 to 18 and Tables 7 to 9 show Reference Example 3 of the short distance correction lens system . FIG. 13 is a lens configuration diagram in the infinity shooting state, FIG. 14 is its aberration diagram, FIG. 15 is its lateral aberration diagram, FIG. 16 is a lens configuration diagram in the close-up shooting state, FIG. 17 is its aberration diagram, FIG. 18 is a lateral aberration diagram thereof. Table 7 shows surface data, Table 8 shows various data, and Table 9 shows aspherical data.

The lens configuration of the reference example 3 is the same as that of the reference example 1 .

(Table 7)
Surface data surface number rd N (d) νd
1 2000.000 2.500 1.74330 49.2
2 46.299 13.572
3 62.822 7.666 1.83400 37.3
4 -1465.488 3.020
5 71.409 7.181 1.49700 81.6
6 -125.149 8.610
7 -96.328 1.800 1.64769 33.8
8 188.921 3.791
9 stops ∞ 6.967
10 -34.872 2.000 1.62004 36.3
11 204.907 8.635 1.49700 81.6
12 -34.890 2.581
13 141.154 4.958 1.69350 53.2
14 * -104.307 d14
15 -560.621 1.650 1.58144 40.9
16 82.691 3.097
17 124.997 5.295 1.80610 33.3
18 -75.920 5.914
19 -59.080 1.650 1.63980 34.6
20 251.608-
* Is a rotationally symmetric aspherical surface.
(Table 8)
Various data
Infinity shooting state Short-distance (-0.75x) shooting state
FNO. 2.88 4.54
f 90.38
W 21.2
Y 34.85 34.85
fB 67.44 82.26
L 167.59 216.81
d14 9.260 43.664
(Table 9)
Aspheric data surface number K A4 A6
14 0.000 0.1048E-05 0.3393E-09

[Reference Example 4]
19 to 24 and Tables 10 to 12 show Reference Example 4 of the short distance correction lens system . 19 is a lens configuration diagram in the infinity shooting state, FIG. 20 is its aberration diagram, FIG. 21 is its lateral aberration diagram, FIG. 22 is a lens configuration diagram in the close-up shooting state, FIG. 23 is its aberration diagram, FIG. 24 is a lateral aberration diagram thereof. Table 10 shows surface data, Table 11 shows various data, and Table 12 shows aspheric data.

The lens configuration of the reference example 4 is the same as that of the reference example 1 except for the following points.
(1) The positive lens 12 of the first lens group G1 is a positive meniscus lens convex toward the object side.

(Table 10)
Surface data surface number rd N (d) νd
1 155.398 2.500 1.70154 41.2
2 37.772 16.030
3 57.814 6.310 1.80518 25.5
4 282.286 3.270
5 60.821 7.410 1.49700 81.6
6 -115.678 8.870
7 -169.067 1.800 1.80518 25.5
8 106.362 4.370
9 stops ∞ 6.960
10 -34.513 2.000 1.74950 35.0
11 274.491 8.640 1.49700 81.6
12 -31.492 0.630
13 97.553 4.960 1.80139 45.5
14 * -115.663 d14
15 -615.431 1.650 1.51742 52.2
16 66.861 3.560
17 126.336 5.300 1.80610 33.3
18 -87.112 7.240
19 -70.372 1.650 1.67270 32.2
20 244.535-
* Is a rotationally symmetric aspherical surface.
(Table 11)
Various data
Infinity shooting state Short-distance (-0.75x) shooting state
FNO. 2.88 4.43
f 89.37
W 21.3
Y 34.85 34.85
fB 67.45 85.93
L 170.49 216.46
d14 9.890 37.382
(Table 12)
Aspheric data surface number K A4 A6
14 0.000 0.9759E-06 0.2538E-09

[Reference Example 5]
25 to 30 and Tables 13 to 15 show Reference Example 5 of the short distance correction lens system . FIG. 25 is a lens configuration diagram in the infinity shooting state, FIG. 26 is its aberration diagram, FIG. 27 is its lateral aberration diagram, FIG. 28 is a lens configuration diagram in the close-up shooting status, FIG. 29 is its aberration diagram, FIG. 30 is a lateral aberration diagram thereof. Table 13 shows surface data, Table 14 shows various data, and Table 15 shows aspherical data.

The lens configuration of the reference example 5 is the same as that of the reference example 4 .

(Table 13)
Surface data surface number rd N (d) νd
1 350.638 2.500 1.71300 53.9
2 41.817 13.010
3 58.203 7.060 1.83400 37.3
4 782.988 4.080
5 64.861 11.000 1.49700 81.6
6 -121.379 7.520
7 -139.008 1.800 1.69895 30.0
8 113.364 5.490
9 stops ∞ 6.260
10 -36.570 2.000 1.80610 33.3
11 269.178 8.640 1.49700 81.6
12 -33.267 0.250
13 99.829 4.960 1.80101 40.9
14 * -110.071 d14
15 -1728.669 1.650 1.54814 45.8
16 70.447 3.340
17 118.910 5.300 1.83400 37.3
18 -78.477 5.090
19 -60.343 1.650 1.59551 39.2
20 138.948-
* Is a rotationally symmetric aspherical surface.
(Table 14)
Various data
Infinity shooting state Short-distance (-0.75x) shooting state
FNO. 2.88 4.58
f 89.99
W 21.2
Y 34.85 34.85
fB 67.78 87.57
L 167.48 216.70
d14 8.100 37.532
(Table 15)
Aspheric data surface number K A4 A6
14 0.000 0.9125E-06 0.2098E-09

[Reference Example 6]
FIGS. 31 to 36 and Tables 16 to 18 show Reference Example 6 of the short distance correction lens system . FIG. 31 is a lens configuration diagram in the infinity shooting state, FIG. 32 is its aberration diagram, FIG. 33 is its lateral aberration diagram, FIG. 34 is a lens configuration diagram in the close-up shooting status, FIG. 35 is its aberration diagram, FIG. 36 is a lateral aberration diagram thereof. Table 16 shows surface data, Table 17 shows various data, and Table 18 shows aspherical data.

The lens configuration of the reference example 6 is the same as that of the reference example 1 except for the following points.
(1) The positive lens 12 of the first lens group G1 is a planoconvex positive lens that is convex on the object side.
(2) The negative lens (negative lens concave on the image side) 21 of the second lens group G2 is a negative meniscus lens convex on the object side.

(Table 16)
Surface data surface number rd N (d) νd
1 305.177 2.500 1.72916 54.7
2 41.868 14.230
3 58.765 7.200 1.74950 35.3
4 ∞ 3.020
5 63.462 10.890 1.49700 81.6
6 -119.178 8.580
7 -117.585 1.800 1.64769 33.8
8 101.926 4.350
9 stops ∞ 6.720
10 -34.067 2.000 1.72825 28.3
11 449.442 8.640 1.49700 81.6
12 -33.304 0.250
13 88.965 4.960 1.80610 40.7
14 * -109.811 d14
15 594.325 1.650 1.72825 28.3
16 66.581 5.540
17 120.345 5.300 1.80518 25.5
18 -77.738 6.240
19 -60.917 1.650 1.64769 33.8
20 185.828-
* Is a rotationally symmetric aspherical surface.
(Table 17)
Various data
Infinity shooting state Short-distance (-0.75x) shooting state
FNO. 2.88 4.52
f 89.77
W 21.2
Y 34.85 34.85
fB 67.37 94.82
L 168.39 213.83
d14 5.500 23.496
(Table 18)
Aspheric data surface number K A4 A6
14 0.000 0.1192E-05 0.1752E-09

[Reference Example 7]
37 to 42 and Tables 19 to 21 show Reference Example 7 of the short distance correction lens system . FIG. 37 is a lens configuration diagram in the infinity photographing state, FIG. 38 is its aberration diagram, FIG. 39 is its lateral aberration diagram, FIG. 40 is a lens configuration diagram in the close-up shooting state, FIG. 41 is its aberration diagram, FIG. 42 is a lateral aberration diagram thereof. Table 19 shows surface data, Table 20 shows various data, and Table 21 shows aspherical data.

The lens configuration of the reference example 7 is the same as that of the reference example 1 except for the following points.
(1) The negative lens (negative lens concave on the image side) 21 of the second lens group G2 is a negative meniscus lens convex on the object side.

(Table 19)
Surface data surface number rd N (d) νd
1 2000.000 2.500 1.77250 49.6
2 45.692 11.540
3 59.646 7.490 1.72342 38.0
4 -677.375 3.020
5 61.512 11.000 1.49700 81.6
6 -123.115 9.620
7 -102.040 1.800 1.56732 42.8
8 114.686 4.260
9 stop ∞ 7.430
10 -32.034 2.000 1.71736 29.5
11 362.902 8.640 1.49700 81.6
12 -32.023 0.250
13 78.013 5.850 1.80 139 45.5
14 * -125.242 d14
15 300.258 1.650 1.72825 28.3
16 59.337 3.910
17 117.738 5.300 1.84666 23.8
18 -79.123 5.280
19 -64.463 1.650 1.69895 30.0
20 163.152-
* Is a rotationally symmetric aspherical surface.
(Table 20)
Various data
Infinity shooting state Short-distance (-0.50x) shooting state
FNO. 2.88 4.03
f 90.14
W 21.1
Y 34.85 34.85
fB 68.83 91.95
L 167.52 200.37
d14 5.500 15.222
(Table 21)
Aspheric data surface number K A4 A6
14 0.000 0.1246E-05 0.7829E-10

[Reference Example 8]
43 to 48 and Tables 22 to 24 show Reference Example 8 of the short distance correction lens system according to the present invention. 43 is a lens configuration diagram in the infinity shooting state, FIG. 44 is its aberration diagram, FIG. 45 is its lateral aberration diagram, FIG. 46 is a lens configuration diagram in the close-up shooting status, FIG. 47 is its aberration diagram, FIG. 48 is a lateral aberration diagram thereof. Table 22 shows surface data, Table 23 shows various data, and Table 24 shows aspherical data.

The lens configuration of the reference example 8 is the same as that of the reference example 7 .

(Table 22)
Surface data surface number rd N (d) νd
1 703.402 2.500 1.83481 42.7
2 47.731 11.460
3 59.240 7.470 1.80610 33.3
4 -1086.874 3.020
5 66.760 11.000 1.49700 81.6
6 -127.022 6.290
7 -111.960 1.800 1.56732 42.8
8 108.311 5.400
9 stop ∞ 10.550
10 -31.687 2.000 1.69895 30.0
11 159.164 8.640 1.49700 81.6
12 -31.846 0.250
13 66.774 4.960 1.80139 45.5
14 * -154.236 d14
15 292.195 1.650 1.69895 30.0
16 52.984 4.050
17 117.847 5.300 1.80518 25.5
18 -70.243 4.890
19 -59.221 1.650 1.63980 34.6
20 142.919-
* Is a rotationally symmetric aspherical surface.
(Table 23)
Various data
Infinity shooting state Short-distance (-0.50x) shooting state
FNO. 2.88 4.09
f 90.23
W 21.1
Y 34.85 34.85
fB 68.91 97.16
L 167.29 202.16
d14 5.500 12.125
(Table 24)
Aspheric data surface number K A4 A6
14 0.000 0.1254E-05 -0.2444E-10

[Reference Example 9]
49 to 54 and Tables 25 to 27 show Reference Example 9 of the short distance correction lens system . 49 is a lens configuration diagram in the infinity shooting state, FIG. 50 is its aberration diagram, FIG. 51 is its lateral aberration diagram, FIG. 52 is a lens configuration diagram in the close-up shooting state, FIG. 53 is its aberration diagram, FIG. 54 is a lateral aberration diagram thereof. Table 25 shows surface data, Table 26 shows various data, and Table 27 shows aspheric data.

The lens configuration of the reference example 9 is the same as that of the reference example 2 .

(Table 25)
Surface data surface number rd N (d) νd
1 1989.085 2.500 1.72916 54.7
2 44.288 11.690
3 56.012 7.230 1.80450 39.6
4 1118.068 3.500
5 69.627 6.740 1.48749 70.4
6 -121.000 6.190
7 -146.248 1.800 1.56732 42.8
8 118.599 5.860
9 stop ∞ 11.870
10 -33.941 2.000 1.68893 31.2
11 99.993 9.620 1.49700 81.6
12 -33.716 0.250
13 51.385 6.280 1.75501 51.2
14 * -227.297 d14
15 277.107 1.650 1.72342 38.0
16 45.410 4.940
17 123.939 5.300 1.80518 25.5
18 -71.332 5.270
19 -72.121 1.650 1.67270 32.2
20 141.151-
* Is a rotationally symmetric aspherical surface.
(Table 26)
Various data
Infinity shooting state Short-distance (-0.50x) shooting state
FNO. 2.88 4.14
f 90.25
W 21.1
Y 34.85 34.85
fB 68.02 100.64
L 167.86 204.31
d14 5.500 9.327
(Table 27)
Aspheric data surface number K A4 A6
14 0.000 0.1793E-05 -0.1276E-09

[Reference Example 10]
55 to 60 and Tables 28 to 30 show Reference Example 10 of the short distance correction lens system . FIG. 55 is a lens configuration diagram in the infinity shooting state, FIG. 56 is its aberration diagram, FIG. 57 is its lateral aberration diagram, FIG. 58 is a lens configuration diagram in the close-up shooting status, FIG. 59 is its aberration diagram, FIG. 60 is a lateral aberration diagram thereof. Table 28 shows surface data, Table 29 shows various data, and Table 30 shows aspherical data.

The lens configuration of the reference example 10 is the same as that of the reference example 7 except for the following points.
(1) During focusing from an object at infinity to an object at a short distance, the first lens group G1 is moved (drawn) toward the object side, and the second lens group G2 is fixed with respect to the image plane I (optical axis). Does not move in the direction).

(Table 28)
Surface data surface number rd N (d) νd
1 1237.863 2.100 1.80610 40.7
2 42.391 10.630
3 60.652 6.620 1.80610 33.3
4 -217.593 3.030
5 59.015 9.000 1.48749 70.4
6 -111.786 6.010
7 -106.004 2.320 1.74950 35.3
8 116.344 4.650
9 stop ∞ 7.230
10 -34.530 2.000 1.68893 31.2
11 205.036 8.530 1.49700 81.6
12 -34.186 1.660
13 164.190 5.340 1.80139 45.5
14 * -82.539 d14
15 799.831 2.080 1.76200 40.1
16 54.121 3.190
17 61.840 6.240 1.80610 33.3
18 -85.825 5.780
19 -67.931 1.690 1.67270 32.2
20 131.352-
* Is a rotationally symmetric aspherical surface.
(Table 29)
Various data
Infinity shooting state Short-distance (-0.50x) shooting state
FNO. 2.88 3.80
f 90.05
W 21.2
Y 34.85 34.85
fB 70.75 70.75
L 164.35 191.05
d14 5.500 32.202
(Table 30)
Aspheric data surface number K A4 A6
14 0.000 0.8540E-06 0.3276E-09

[Reference Example 11]
61 to 66 and Tables 31 to 33 show Reference Example 11 of the short distance correction lens system . 61 is a lens configuration diagram in the infinity shooting state, FIG. 62 is its aberration diagram, FIG. 63 is its lateral aberration diagram, FIG. 64 is a lens configuration diagram in the close-up shooting state, FIG. 65 is its aberration diagram, FIG. 66 is a lateral aberration diagram thereof. Table 31 shows surface data, Table 32 shows various data, and Table 33 shows aspherical data.

The lens configuration of the reference example 11 is the same as that of the reference example 10 .

(Table 31)
Surface data surface number rd N (d) νd
1 2000.000 2.100 1.80420 46.5
2 41.936 11.950
3 62.301 6.620 1.83400 37.3
4 -244.596 3.030
5 58.976 9.000 1.49700 81.6
6 -112.192 6.000
7 -109.325 2.320 1.70154 41.2
8 102.768 4.190
9 stops ∞ 8.340
10 -34.405 2.000 1.71736 29.5
11 1257.628 8.530 1.49700 81.6
12 -33.940 0.330
13 167.258 5.340 1.80139 45.5
14 * -84.808 d14
15 240.443 2.000 1.72342 38.0
16 53.119 4.710
17 58.351 6.240 1.64769 33.8
18 -82.972 6.820
19 -65.134 1.690 1.62004 36.3
20 130.440-
* Is a rotationally symmetric aspherical surface.
(Table 32)
Various data
Infinity shooting state Short distance (-0.70x) shooting state
FNO. 2.88 4.15
f 89.42
W 21.4
Y 34.85 34.85
fB 67.69 67.69
L 164.40 201.19
d14 5.500 42.287
(Table 33)
Aspheric data surface number K A4 A6
14 0.000 0.9994E-06 0.4657E-09

[Reference Example 12]
67 to 72 and Tables 34 to 36 show Reference Example 12 of the short distance correction lens system . 67 is a lens configuration diagram in the infinity shooting state, FIG. 68 is its aberration diagram, FIG. 69 is its lateral aberration diagram, FIG. 70 is a lens configuration diagram in the close-up shooting state, FIG. 71 is its aberration diagram, FIG. 72 is a lateral aberration diagram thereof. Table 34 shows surface data, Table 35 shows various data, and Table 36 shows aspherical data.

The lens configuration of the reference example 12 is the same as that of the reference example 10 except for the following points.
(1) The negative lens 15 of the first lens group G1 is a plano-concave negative lens concave on the object side.
(2) The positive lens 16 of the first lens group G1 is a planoconvex positive lens that is convex on the image side.
(3) The negative lens (negative lens concave on the image side) 21 of the second lens group G2 is a biconcave negative lens.

(Table 34)
Surface data surface number rd N (d) νd
1 1990.687 2.100 1.72916 54.7
2 40.648 12.410
3 58.457 6.860 1.80450 39.6
4 -340.254 3.030
5 72.046 10.000 1.49700 81.6
6 -97.152 6.010
7 -79.731 2.000 1.63980 34.6
8 190.437 5.090
9 stop ∞ 6.190
10 -41.845 2.000 1.75520 27.5
11 ∞ 7.120 1.49700 81.6
12 -39.128 0.740
13 267.350 5.340 1.80101 40.9
14 * -74.918 d14
15 -247.967 2.000 1.74400 44.9
16 53.884 3.850
17 67.090 6.610 1.80450 39.6
18 -74.942 7.780
19 -66.282 1.500 1.60342 38.0
20 256.520-
* Is a rotationally symmetric aspherical surface.
(Table 35)
Various data
Infinity shooting state Short-distance (-0.70x) shooting state
FNO. 2.88 4.21
f 89.46
W 21.4
Y 34.85 34.85
fB 68.27 68.27
L 164.40 200.93
d14 5.500 42.029
(Table 36)
Aspheric data surface number K A4 A6
14 0.000 0.1130E-05 0.6034E-09

[Reference Example 13]
73 to 78 and Tables 37 to 39 show Reference Example 13 of the short distance correction lens system . 73 is a lens configuration diagram in the infinity shooting state, FIG. 74 is its aberration diagram, FIG. 75 is its lateral aberration diagram, FIG. 76 is a lens configuration diagram in the close-up shooting state, FIG. 77 is its aberration diagram, FIG. 78 is a lateral aberration diagram thereof. Table 37 shows surface data, Table 38 shows various data, and Table 39 shows aspheric data.

The lens configuration of the reference example 13 is the same as that of the reference example 12 except for the following points.
(1) The negative lens 15 of the first lens group G1 is a negative meniscus lens convex on the image side.
(2) The positive lens 16 of the first lens group G1 is a positive meniscus lens convex on the image side.

(Table 37)
Surface data surface number rd N (d) νd
1 1983.218 2.100 1.77250 49.6
2 41.543 12.480
3 63.357 6.970 1.83400 37.3
4 -276.955 3.030
5 63.077 10.000 1.49700 81.6
6 -101.306 6.010
7 -95.007 1.500 1.67270 32.2
8 119.475 6.090
9 stops ∞ 6.980
10 -35.048 1.500 1.68893 31.2
11 -1097.973 7.490 1.49700 81.6
12 -34.507 0.250
13 200.394 5.330 1.80139 45.5
14 * -80.342 d14
15 -524.733 1.500 1.74330 49.2
16 52.116 3.270
17 60.636 6.920 1.70154 41.2
18 -75.048 8.930
19 -64.231 1.500 1.59551 39.2
20 283.354-
* Is a rotationally symmetric aspherical surface.
(Table 38)
Various data
Infinity shooting state Short-distance (-0.50x) shooting state
FNO. 2.88 3.78
f 89.69
W 21.3
Y 34.85 34.85
fB 67.04 67.04
L 164.39 189.03
d14 5.500 30.139
(Table 39)
Aspheric data surface number K A4 A6
14 0.000 0.1109E-05 0.4896E-09

[Numerical Example 1]
79 to 84 and Tables 40 to 42 show Numerical Example 1 of the short-distance correction lens system according to the present invention. 79 is a lens configuration diagram in the infinity shooting state, FIG. 80 is its aberration diagram, FIG. 81 is its lateral aberration diagram, FIG. 82 is a lens configuration diagram in the close-up shooting state, FIG. 83 is its aberration diagram, FIG. 84 is a lateral aberration diagram thereof. Table 40 shows surface data, Table 41 shows various data, and Table 42 shows aspherical data.

The numerical example 1 mainly differs from the reference examples 1 to 13 in the lens configuration of the first lens group G1 (how to separate the lens groups).

The first lens group G1, in order from the object side, includes a first-a lens group G1a having a positive refractive power, a first-b lens group G1b having a negative refractive power, an aperture stop S, and a first-c lens group G1c having a positive refractive power. Become.
The first-a lens group G1a includes, in order from the object side, a negative meniscus lens 11 ′ convex toward the object side, a positive meniscus lens 12 ′ convex toward the object side, and a biconvex positive lens 13 ′.
The first-b lens group G1b is composed of a biconcave negative lens (a negative lens concave on the image side) 14 'and a positive meniscus lens convex on the object side (positive concave lens on the image side) 15'. It consists of a lens.
The first c lens group G1c includes, in order from the object side, a cemented lens of a biconcave negative lens 16 ′ and a biconvex positive lens 17 ′, and a biconvex positive lens 18 ′, which are sequentially positioned from the object side. The biconvex positive lens 18 ′ has an aspheric image side surface.

  The second lens group G2 includes, in order from the object side, a biconcave negative lens (negative lens concave on the image side) 21, a biconvex positive lens 22, and a biconcave negative lens (negative lens concave on the object side) 23. .

(Table 40)
Surface data surface number rd N (d) νd
1 473.951 2.000 1.69680 55.5
2 42.407 15.520
3 56.655 7.090 1.83400 37.3
4 617.022 4.080
5 81.434 8.290 1.49700 81.6
6 -137.766 6.930
7 -338.338 1.450 1.69895 30.0
8 31.510 5.320 1.80518 25.5
9 85.195 5.880
10 stops ∞ 7.050
11 -39.794 2.000 1.75520 27.5
12 67.154 9.200 1.49700 81.6
13 -37.583 1.400
14 50.849 6.040 1.80 101 40.9
15 * -174.666 d15
16 -4275.941 1.500 1.67270 32.2
17 44.710 5.160
18 137.335 5.350 1.80518 25.5
19 -73.119 5.110
20 -104.080 1.450 1.70154 41.2
21 145.257-
* Is a rotationally symmetric aspherical surface.
(Table 41)
Various data
Infinity shooting state Short-distance (-0.60x) shooting state
FNO. 2.87 4.32
f 90.45
W 21.0
Y 34.85 34.85
fB 66.76 101.86
L 173.26 213.84
d15 5.680 11.159
(Table 42)
Aspheric data surface number K A4 A6
15 0.000 0.1916E-05 -0.9666E-10

[Numerical Example 2]
85 to 90 and Tables 43 to 45 show Numerical Example 2 of the short-distance correction lens system according to the present invention. FIG. 85 is a lens configuration diagram in the infinity shooting state, FIG. 86 is its aberration diagram, FIG. 87 is its lateral aberration diagram, FIG. 88 is a lens configuration diagram in the close-up shooting state, FIG. 89 is its aberration diagram, FIG. 90 is a lateral aberration diagram thereof. Table 43 shows surface data, Table 44 shows various data, and Table 45 shows aspherical data.

The lens configuration of Numerical Example 2 is the same as that of Numerical Example 1 except for the following points.
(1) The negative lens 21 of the second lens group G2 is a negative meniscus lens convex toward the object side.

(Table 43)
Surface data surface number rd N (d) νd
1 313.004 2.000 1.83481 42.7
2 42.890 11.700
3 56.534 7.540 1.80610 33.3
4 1344.027 5.180
5 70.142 7.260 1.49700 81.6
6 -126.482 7.850
7 -253.610 1.450 1.63980 34.6
8 33.519 4.750 1.80518 25.5
9 74.839 6.130
10 stops ∞ 6.640
11 -38.315 1.400 1.72825 28.3
12 58.634 9.660 1.49700 81.6
13 -35.914 0.750
14 58.416 7.250 1.80610 40.7
15 * -183.734 d15
16 2478.431 1.550 1.63980 34.6
17 49.802 4.900
18 126.215 5.570 1.80610 33.3
19 -69.406 4.080
20 -65.521 1.450 1.56883 56.0
21 146.337-
* Is a rotationally symmetric aspherical surface.
(Table 44)
Various data
Infinity shooting state Short-distance (-0.50x) shooting state
FNO. 2.85 4.06
f 90.12
W 21.1
Y 34.85 34.85
fB 69.09 98.18
L 171.88 207.25
d15 5.680 11.958
(Table 45)
Aspheric data surface number K A4
15 0.000 0.1173E-05

[Numerical Example 3]
FIGS. 91 to 96 and Tables 46 to 48 show Numerical Example 3 of the short-range correction lens system according to the present invention. FIG. 91 is a lens configuration diagram in the infinity shooting state, FIG. 92 is its aberration diagram, FIG. 93 is its lateral aberration diagram, FIG. 94 is a lens configuration diagram in the close-up shooting state, FIG. 95 is its aberration diagram, FIG. 96 is a lateral aberration diagram thereof. Table 46 shows surface data, Table 47 shows various data, and Table 48 shows aspherical data.

The lens configuration of Numerical Example 3 is the same as that of Numerical Example 1 except for the following points.
(1) The positive lens 12 ′ of the 1a lens group G1a is a biconvex positive lens. The biconvex positive lens 12 'has an aspheric object side surface.
(2) The negative lens 21 of the second lens group G2 is a plano-concave negative lens concave on the image side.

(Table 46)
Surface data surface number rd N (d) νd
1 2254.961 2.000 1.65 160 58.4
2 42.516 15.530
3 * 52.658 8.500 1.72916 54.7
4 -473.334 2.630
5 106.175 5.470 1.49700 81.6
6 -198.050 8.690
7 -238.065 1.450 1.59551 39.2
8 34.324 4.410 1.80518 25.5
9 67.445 6.900
10 stops ∞ 6.250
11 -43.265 1.400 1.71736 29.5
12 45.438 8.080 1.48749 70.4
13 -54.875 0.250
14 69.236 6.250 1.80139 45.5
15 * -80.649 d15
16 ∞ 1.500 1.53172 48.8
17 50.628 4.960
18 156.419 4.380 1.80610 33.3
19 -115.982 3.000
20 -427.329 1.450 1.72342 38.0
21 152.155-
* Is a rotationally symmetric aspherical surface.
(Table 47)
Various data
Infinity shooting state Short-distance (-0.50x) shooting state
FNO. 2.87 4.06
f 89.86
W 21.3
Y 34.85 34.85
fB 74.69 104.66
L 173.47 210.47
d15 5.680 12.710
(Table 48)
Aspheric data surface number K A4
3 0.000 -0.9260E-07
15 0.000 0.1535E-05

Table 49 shows values for the conditional expressions of Reference Example 1-13 and Numerical Example 1-3 . Here, the numerical values corresponding to conditional expressions (8) and (9) indicate numerical values for the positive lens closest to the object among the positive lenses in the first lens group G1. Since the reference examples 1 to 13 are different from those in the numerical examples 1 to 3 in terms of the lens configuration of the first lens group G1 (how to separate the lens groups), the conditional expressions (11) to (14) The numerical value corresponding to the conditional expression cannot be calculated. On the other hand, in the numerical examples 1 to 3 , since the lens configuration of the second lens group G2 as a premise is common to the reference examples 1 to 13 , the numerical values corresponding to the conditional expressions (1) to (10) Can be calculated.
(Table 49)
Reference Example 1 Reference Example 2 Reference Example 3 Reference Example 4 Reference Example 5
Conditional expression (1) -0.77 -1.04 -0.74 -0.80 -0.92
Conditional expression (2) 0.211 0.199 0.210 0.317 0.229
Conditional expression (3) 0.46 0.43 0.44 0.52 0.47
Conditional expression (4) 0.25 0.22 0.26 0.37 0.27
Conditional expression (5) 39.22 36.30 34.57 32.17 39.22
Conditional expression (6) 1.806 1.744 1.743 1.702 1.713
Conditional expression (7) 40.73 44.90 49.22 41.15 53.94
Conditional expression (8) 1.806 1.805 1.834 1.805 1.834
Conditional expression (9) 33.27 39.64 37.34 25.46 37.34
Conditional expression (10) 0.105 0.205 0.301 0.402 0.502
Conditional expression (11)-----
Conditional expression (12)-----
Conditional expression (13)-----
Conditional expression (14)-----
Reference Example 6 Reference Example 7 Reference Example 8 Reference Example 9 Reference Example 10
Conditional expression (1) -1.25 -1.49 -1.44 -1.39 -1.15
Conditional expression (2) 0.361 0.406 0.418 0.649 0.306
Conditional expression (3) 0.61 0.64 0.65 0.68 0.34
Conditional expression (4) 0.42 0.41 0.46 0.64 0.30
Conditional expression (5) 33.84 30.05 34.57 32.17 32.17
Conditional expression (6) 1.729 1.773 1.835 1.729 1.806
Conditional expression (7) 54.67 49.62 42.72 54.67 40.73
Conditional expression (8) 1.750 1.723 1.806 1.805 1.806
Conditional expression (9) 35.27 37.99 33.27 39.64 33.27
Conditional expression (10) 0.604 0.704 0.810 0.895 (0)
Conditional expression (11)-----
Conditional expression (12)-----
Conditional expression (13)-----
Conditional expression (14)-----
Reference Example 11 Reference Example 12 Reference Example 13
Conditional expression (1) -1.57 -0.64 -0.82
Conditional expression (2) 0.312 0.275 0.323
Conditional expression (3) 0.45 0.25 0.32
Conditional expression (4) 0.33 0.36 0.44
Conditional expression (5) 36.30 38.01 39.22
Conditional expression (6) 1.804 1.729 1.773
Conditional expression (7) 46.50 54.67 49.62
Conditional expression (8) 1.834 1.805 1.834
Conditional expression (9) 37.34 39.64 37.34
Conditional expression (10) (0) (0) (0)
Conditional expression (11)---
Conditional expression (12)---
Conditional expression (13)---
Conditional expression (14)---
Example 1 Example 2 Example 3
Conditional expression (1) -0.98 -1.04 -1.00
Conditional expression (2) 0.970 0.426 1.922
Conditional expression (3) 0.61 0.52 0.43
Conditional expression (4) 0.80 0.52 0.70
Conditional expression (5) 41.15 56.04 37.99
Conditional expression (6) 1.697 1.835 1.652
Conditional expression (7) 55.46 42.72 58.40
Conditional expression (8) 1.834 1.806 1.729
Conditional expression (9) 37.34 33.27 54.67
Conditional expression (10) 0.865 0.822 0.810
Conditional expression (11) 30.05 34.57 39.22
Conditional expression (12) 4.45 9.27 13.62
Conditional expression (13) 1.699 1.640 1.596
Conditional expression (14) 1.805 1.805 1.805

As is clear from Table 49, Reference Examples 1 to 13 satisfy the conditional expressions (1) to (9), and Reference Examples 1 to 9 satisfy the conditional expression (10). Numerical Examples 1 to 3 satisfy the conditional expressions (1) to (14). As is apparent from the various aberration diagrams, the various aberrations are corrected relatively well.

G1 First lens unit 11 having a positive refractive power 11 Negative lens (negative lens concave on the image side)
DESCRIPTION OF SYMBOLS 12 Positive lens 13 Positive lens 14 Negative lens 15 Negative lens 16 Positive lens 17 Positive lens G1a 1a lens group 11 'with positive refractive power Negative lens 12' Positive lens 13 'Positive lens G1b 1b lens group with negative refractive power 14 'negative lens (negative lens concave on the image side)
15 'positive lens (positive lens concave on the image side)
G1c First lens group 16 ′ having positive refractive power 17 ′ Negative lens 17 ′ Positive lens 18 ′ Positive lens G2 Second lens group 21 having negative refractive power Negative lens (negative lens concave on the image side)
22 Positive lens 23 Negative lens (negative lens concave on the object side)
S Aperture stop I Image plane

Claims (13)

In order from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power are provided. At the time of focusing from an infinite object to a close object, at least the first lens unit is located on the object side. In moving short-range correction lens system,
The first lens group includes, in order from the object side, a first-a lens group having a positive refractive power, a first-b lens group having a negative refractive power, an aperture stop, and a first-c lens group having a positive refractive power.
The 1b lens group is composed of a cemented lens of a negative lens concave on the image side and a positive lens concave on the image side, which are sequentially located from the object side.
The second lens group includes , in order from the object side, a negative lens concave on the image side, a positive lens, and a negative negative lens on the object side .
A short-distance correction lens system characterized by satisfying the following conditional expression (12):
_{(12) 0 <νd 1bn -νd} 1bp <20
However,
νd _1bn : Abbe number for the d-line of the negative lens in the 1b lens group,
νd _1bp : Abbe number with respect to d-line of the positive lens in the 1b lens group. 2. The short distance correction lens system according to claim 1, wherein the short distance correction lens system satisfies the following conditional expression (1).
(1) −1.6 <(R _21i + R _21O ) / (R _21i −R _21O ) <− 0.6
However,
R _21i : radius of curvature of the image side surface of the negative lens concave to the image side in the second lens group,
R _21O : the radius of curvature of the object side surface of the negative lens which is concave on the image side in the second lens unit. 3. The short distance correction lens system according to claim 1, wherein the short distance correction lens system satisfies the following conditional expression (2).
(2) 0.1 <R _23O / f ₂ <2.0
However,
R _23O : radius of curvature of the object side surface of the negative lens concave on the object side in the second lens group,
f ₂ : focal length of the second lens group. 4. The short distance correction lens system according to claim 1, wherein the short distance correction lens system satisfies the following conditional expression (3).
(3) 0.2 <f ₂₁ / f ₂ <0.7
However,
f ₂₁ : the focal length of the negative lens concave on the image side in the second lens group,
f ₂ : focal length of the second lens group. 5. The short distance correction lens system according to claim 1, wherein the short distance correction lens system satisfies the following conditional expression (4).
(4) 0.2 <f ₂₃ / f ₂ <0.9
However,
f ₂₃ : focal length of negative lens concave on the object side in the second lens group,
f ₂ : focal length of the second lens group. 6. The short distance correction lens system according to claim 1, wherein the short distance correction lens system satisfies the following conditional expression (5).
(5) νd ₂₃ <60
However,
νd ₂₃ : Abbe number with respect to the d-line of the negative lens concave on the object side in the second lens group.   7. The short distance correction lens system according to claim 1, wherein the first lens group is positioned closest to the object side and has a negative negative lens on the image side. system. 8. The short distance correction lens system according to claim 7, wherein the short distance correction lens system satisfies the following conditional expressions (6) and (7).
(6) nd ₁₁ > 1.65
(7) νd ₁₁ > 40
However,
nd ₁₁ : refractive index with respect to d line of a negative lens which is concave on the image side located closest to the object side in the first lens group
νd ₁₁ : Abbe number with respect to the d-line of the negative lens on the image side that is located closest to the object side in the first lens group. 9. The short distance correction lens system according to claim 1, wherein the first lens group has at least one positive lens, and satisfies the following conditional expressions (8) and (9): A short-range correction lens system.
(8) nd _P1 > 1.7
(9) νd _P1 <60
However,
nd _P1 : refractive index with respect to d-line of at least one positive lens among at least one positive lens in the first lens group,
νd _P1 : Abbe number of at least one positive lens of at least one positive lens in the first lens group with respect to the d-line. 10. The short distance correction lens system according to claim 1, wherein the second lens group moves toward the object side with a different amount of movement from the first lens group during focusing from an infinite object to a short distance object. A short-distance correction lens system that moves and satisfies the following conditional expression (10):
(10) 0.1 <Δd2 / Δd1 <0.9
However,
Δd1: Amount of movement of the first lens unit during focusing from an object at infinity to a near object;
Δd2: The amount of movement of the second lens group during focusing from an object at infinity to a near object.   10. The short distance correction lens system according to claim 1, wherein the second lens group is fixed with respect to the image plane during focusing from an object at infinity to a short distance object. system. 12. The short distance correction lens system according to claim 1, wherein the short distance correction lens system satisfies the following conditional expression (11).
(11) νd _1bn > 30
However,
νd _1bn : Abbe number for the d-line of the negative lens in the 1b lens group. 13. The short distance correction lens system according to claim 1, wherein the short distance correction lens system satisfies the following conditional expressions (13) and (14).
(13) nd _1bn <1.7
(14) nd _1bp > 1.8
However,
nd _1bn : refractive index with respect to d-line of the negative lens in the 1b lens group,
nd _1bp : Refractive index with respect to d-line of the positive lens in the 1b lens group.

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