JPH0217087B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field The present invention is a macro lens for medium format cameras of 6 x 4.5 cm and 6 x 7 cm, which has a semi-telephoto focal length and is a high-performance semi-telephoto lens in all shooting ranges from infinite objects to life size. This is related to macro lenses. b. Prior art and its problems Conventional semi-telephoto macro lenses for medium format cameras of 6 x 4.5 and 6 x 7 cm use a method of focusing using the entire lens, so the amount of lens extension is large, and the maximum magnification is was up to 1/2 times as large. Therefore, in order to increase the magnification to 1/2 or more, there was a problem in that accessories such as a close-up ring and a close-up helicoid were required. Furthermore, in terms of performance, there was a problem in that the larger the magnification, the greater the deterioration in performance. Conventionally, semi-telephoto lenses for 35mm cameras have been made up of a positive first lens group and a negative second lens group, with the negative second lens group fixed and the entire positive first lens group or the first It is known that the lens group is further divided into two groups and moved separately, but if the second lens group is fixed, the degree of freedom in focusing is reduced by one, and the first lens group is moved separately. This increases the burden, and furthermore, if the 35 mm version camera lens is expanded to 6 x 4.5 or 6 x 7 cm version, the size will increase by 1.5 to 2 times and the aberration will also increase by 1.5 to 2 times, so it will not be possible to continue as it is. There was a problem that I couldn't use it. c. Purpose The present invention was made to solve the above-mentioned problems, and is a macro lens for medium size cameras of 6 x 4.5 cm and 6 x 7 cm, which has a focal length of a semi-telephoto lens. , the distance from the lens to the object (less than
The objective is to provide a compact semi-telephoto macro lens that can provide a large WD (abbreviated as WD) and has high performance in all shooting ranges from infinite objects to life-size objects. d Means for solving the problem The semi-telephoto macro lens of the present invention has the following features from the object side:
In a semi-telephoto macro lens consisting of a first lens group having a positive focal length and a second lens group having a negative focal length, the first lens group , both the second lens group are moved to the object side to perform focusing, and (1) 1.2<f/f〓<1.7 (2) 0.0＜X〓/X〓＜0.5 where f: when an infinite object Focal length of the entire system f〓: Focal length of the first lens group X〓: Amount of extension of the first lens group at maximum magnification Characterized by satisfaction. In the semi-telephoto macro lens having the above characteristics, the first lens group includes, from the object side, a positive lens convex to the object side, a positive meniscus lens convex to the object side, and a negative meniscus lens concave to the image side. The 1a lens group consists of a composite lens, a positive lens that is convex on the image side, a negative lens that has a concave diverging surface with a large curvature on the object side, and a positive lens that has a convergent surface with a large curvature that is convex on the image side. The first part consists of glued lenses.
1b lens group, and (3) 0.2＜f/f〓 _a ＜0.5 (4) −0.4＜r〓 _bN /f＜−0.1 (5) −0.4＜r〓 _bP /f＜−0.1 where f〓 _a : Focal length of the 1a-th lens group r〓 _bN : Radius of curvature of the diverging surface of the 1b-th lens group with a large curvature r〓 _bP : Conditions for the radius of curvature of the converging surface with a large curvature of the 1b-th lens group and the second lens group includes, from the object side, a 2a lens group consisting of a negative lens group having at least one negative lens having a diverging surface with a concave image surface and a large curvature; and the 2a lens group. and a positive second b lens group arranged at a distance from the lens group, and (6) 0.3<f/f〓 _~ 〓 _a <0.9 (7) 0.2<r〓 _aN /f<0.7 (8) 0.07＜l〓 _a〜 〓 _b /f＜0.3 However, _{f〓〜〓 a} : From the first lens group to the second a when an infinite object
Focal length to the lens group r〓 _aN : Radius of curvature of the diverging surface with the largest curvature of the 2a lens group l〓 _a~ 〓 _b : From the first surface (tip) of the 2a lens group to the
It is characterized by satisfying various conditions regarding the distance to the first surface of the 2b lens group. Incidentally, the second a lens group, as described above,
This is a negative lens group that requires at least one negative lens that satisfies condition (7) and has a diverging surface with a concave side surface and a large curvature. , it is more preferable to divide this 2a-th lens group into two negative lenses. In addition, when focusing, this semi-telephoto macro lens can be adjusted to provide even more freedom in focusing by making the distance between the 1a lens group and 1b lens group or between the 2a lens group and 2b lens group variable. This is more preferable because it increases the power and allows each group to be set at a position where aberrations are best balanced at any magnification. e Effect Each of the above conditions will be explained below. Condition (1) relates to the power of the first lens group; if the upper limit is exceeded, it is advantageous to reduce the amount of lens movement, but the power of the first lens group becomes too large and focusing This increases fluctuations in aberrations such as spherical aberration, coma aberration, and curvature of field, which goes against the purpose of achieving high performance in all shooting ranges from infinity to life-size. On the other hand, if the lower limit is exceeded, although it is advantageous for correcting aberrations, the amount of movement of the lens increases, which is contrary to compactness and operability. Condition (2) relates to the relationship between the movement of the first lens group and the second lens group; if the upper limit is exceeded, it is advantageous to increase the WD, but the relationship between the first lens group and the second lens group Since the amount of change in the distance between the lenses becomes smaller, the amount of movement of the lens increases, which is contrary to compactness and operability. On the other hand, if the lower limit is exceeded, the amount of movement of the second lens group becomes small, and the size of the second lens group in the radial direction increases, which goes against the goal of making the lens diameter more compact. Furthermore, if the lower limit is exceeded and the diameter of the second lens group is made small, the amount of peripheral light around the 1:1 magnification will drop sharply, making it possible to take all shots from infinity to 1:1 magnification with just the lens system without using accessories. It defeats the purpose of Conditions (3), (4), and (5) relate to the first lens group. Condition (3) is related to the power arrangement of the 1a lens group; if the upper limit is exceeded, it is advantageous for compactness, but the height of incidence on the diverging surface of the 1b lens group is reduced. , the negative power of the diverging surface must be increased, and the aberration fluctuations with respect to changes in object distance become large. On the other hand, if the lower limit is exceeded, the load on the 1b lens group increases, making it difficult to correct aberrations.If the positive power of the 1b lens group is reduced to correct the aberrations, the amount of extension of the 1st lens group, This also increases the overall length of the lens system, which is contrary to compactness. Condition (4) relates to the power of the divergent surface of the combined lens in the 1b lens group, and is an important condition for reducing fluctuations in aberration when the object distance changes. If the lower limit is exceeded, the effect of the diverging surface becomes too small, resulting in insufficient correction, and changes in spherical aberration and comatic aberration with respect to changes in object distance increase,
It becomes difficult to achieve high performance over the entire range from infinity to the same magnification. On the other hand, if the upper limit is exceeded, the curvature of the diverging surface becomes too large, resulting in excessive correction, and high-order aberrations also occur, which is not preferable. Condition (5) is related to condition (4), but is intended to balance the over aberration generated at the divergent surfaces of the combined lenses of the 1b lens group to some extent within the 1b lens group. If the upper limit is exceeded, the
The curvature of the convergent surface of the combined lens of lens group 1b becomes too large, and the over-correction of aberrations generated on the diverging surface of lens group 1b becomes excessive and under-corrected, and higher-order aberrations also occur, making it difficult to properly correct the aberrations. Not. On the other hand, if the lower limit is exceeded, the over-correction of aberrations generated on the diverging surface will be insufficient, leading to an increase in fluctuations in aberrations with respect to changes in object distance. Conditions (6), (7), and (8) relate to the second lens group. Condition (6) relates to the power arrangement of the 2a-th lens group, and is intended to correct under-aberrations occurring in the first lens group. If the upper limit is exceeded,
The negative power of the 2A lens group becomes smaller, and the divergence becomes smaller, resulting in insufficient correction, and various aberrations such as spherical aberration, coma aberration, and curvature of field change to under-representation as the object distance changes, resulting in infinity. It is not possible to achieve high performance in the entire range from 1x to 1x. On the other hand, if the lower limit is exceeded, the negative power of the 2a lens group becomes too strong, resulting in excessive correction, and when changing the magnification from infinity to equal magnification, the above-mentioned aberrations change excessively, which is inappropriate. Condition (7) concerns the diverging surface with the largest negative power in the 2a lens group; if the upper limit is exceeded, it becomes impossible to correct the various aberrations that occur in the 1st lens group, that is, there is insufficient correction, and conversely, If the lower limit is exceeded, various aberrations will be overcorrected, which is not appropriate. Condition (8) is intended to balance field curvature and distortion; exceeding the upper limit is advantageous in terms of aberration correction, but increases the rear lens diameter, which goes against compactness, and conversely exceeds the lower limit. When it crosses the line, the 2a lens group and the
The distance between the 2b lens groups becomes too small, making it difficult to correct field curvature and distortion. f Examples Examples 1 to 3 of the present invention will be described below. Here, F _Np is the F number, f is the focal length at infinite object distance, ω is the half angle of view at infinite object distance, WD is the distance from the object to the first surface, f _B is the back focus, and r
is the radius of curvature of each lens surface, d is the lens thickness or distance between lens surfaces, N is the d-line refractive index of each lens, and ν is the Abbe number of each lens.

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[Table] g Effects As explained above, according to the present invention, by performing focusing while increasing the distance between the first lens group and the second lens group, compared to the case where the entire lens is moved, Since the same magnification can be obtained with a small amount of movement, it is very effective for compactness and operability. In the case of the present invention, the same magnification was obtained with about half the amount of extension when focusing with the entire lens. When focusing, it is structurally easiest to fix the second lens group, but if it is fixed, the radial size of the second lens group will increase for a medium format camera lens system. If the diameter of the lens is made smaller, the amount of peripheral light will be insufficient near the same magnification. Moving the second lens group toward the object side also makes it possible to maintain balance with the first lens group, which is advantageous for improving performance and increasing WD. Increasing the WD is effective for photographing subjects that cannot be approached unnecessarily, and being able to take pictures up to the same magnification has a very negative impact on operability compared to increasing the magnification with a close-up ring or close-up helicoid. It is also effective. The performance limit of regular 6 x 4.5, 6 x 7 cm macro lenses for medium format cameras is about 1/2x.
When the magnification becomes large, such as 1:1 magnification, it is not practical unless the zoom ratio is narrowed down considerably.However, the present invention has the above-described configuration, and has sufficient performance from the widest aperture, from infinity to 1:1 magnification. You can get a compact semi-telephoto macro lens.

[Brief explanation of drawings]

FIGS. 1, 3, and 5 are lens configuration diagrams of embodiments 1, 2, and 3 of the present invention when an infinite object is used, and FIGS. 2, 4, and 6 are lens configuration diagrams of embodiments 1 and 2 of the present invention, respectively. ,
In the various aberration diagrams in 3, a is an infinite object, b is 1/2 times, and c
is an aberration diagram of 1/1 times. In the figure, r _i is the radius of curvature of each lens surface, d _i is the lens thickness or distance between lens surfaces, F _e is the effective F number for a finite object, and Y is the image height for a finite object.

Claims (1)

[Claims] 1. From the object side, a semi-telephoto macro lens consisting of a first lens group having a positive focal length and a second lens group having a negative focal length, the first lens group and the second lens group having a negative focal length. Focusing is performed by moving both the first and second lens groups toward the object side while increasing the group spacing, and (1) 1.2<f/f〓<1.7 (2) 0.0<X〓 /X〓＜0.5 where f: Focal length of the entire system when an infinite object f〓: Focal length of the first lens group X〓: Extension amount of the first lens group at maximum magnification X〓: At maximum magnification A semi-telephoto macro lens characterized by satisfying various conditions regarding the amount of extension of a second lens group. 2. The first lens group includes, from the object side, a 1a lens group consisting of a positive lens that is convex to the object side, a positive meniscus lens that is convex to the object side, and a negative meniscus lens that is concave to the image plane side; 1b consists of a positive lens that is convex on the image side, a negative lens that has a concave diverging surface with a large curvature on the object side, and a positive lens that has a convergent surface that is convex on the image side and has a large curvature.
(3) 0.2＜f/f〓 _a ＜0.5 (4) −0.4＜r〓 _bN /f＜−0.1 (5) −0.4＜r〓 _bP /f＜−0.1 f〓 _a : Focal length of the 1a-th lens group r〓 _bN : Radius of curvature of the diverging surface with a large curvature of the 1b-th lens group r〓 _bP : Satisfies the conditions for the radius of curvature of the converging surface with a large curvature of the 1b-th lens group A semi-telephoto macro lens according to claim 1, characterized in that: 3. The second lens group includes, from the object side, a lens group 2a, which is a negative lens group having at least one negative lens having a diverging surface with a concave image surface and a large curvature;
and a positive 2b lens group arranged at a distance from the 2a lens group, and (6) 0.3<f/f〓 _~ 〓 _a <0.9 (7) 0.2<r〓 _aN /f＜0.7 (8) 0.07＜l〓 _{a〜〓 b} /f＜0.3 However, _{f〓〜〓 a} : From the first lens group to the second a when an infinite object
Focal length to the lens group r〓 _aN : Radius of curvature of the diverging surface with the largest curvature of the 2a lens group l〓 _a~ 〓 _b : From the first surface (tip) of the 2a lens group to the
2b. The semi-telephoto macro lens according to claim 1, which satisfies various conditions regarding the distance to the first surface of the lens group 2b.