JPH0248623A - Zoom lens for finite distance - Google Patents

Abstract

PURPOSE:To obviate the troublesome operation at the time of closeup photographing and to realize a finite distance use bright zoom lens by constituting the lens system of three lens groups having prescribed refracting power, and also, forming asymmetrically the whole lens constitution, and also, satisfying specific conditional expressions. CONSTITUTION:The zoom lens has a first group I of positive refracting power, a second group II of negative refracting power and a third group III of positive refracting power in order from an object side, both lens groups of a first group I and a third group III are moved on an optical axis symmetrically as indicated with an arrow against a second group II, and also, the whole system is moved as one body on the optical axis and in a state that a distance between the object and an image is maintained constant, variable power extending from low magnification to high magnification is executed. Subsequently, by specifying the refracting power of a first and a second groups I, II so as to satisfy conditional expressions, various aberrations at the time of closeup photographing are corrected satisfactorily, and a high optical performance can be obtained extending over a wide photographing magnification range.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a finite distance zoom lens suitable for 35mm single-lens reflex cameras, still video cameras, etc. This invention relates to a finite-distance zoom lens that is suitable for close-up photography by changing the photographing magnification, for example, in combination with a bellows or the like.

(Prior Art) Traditionally, as photographing systems for close-up photography with a low magnification of about 0.5 to 3.0, there have been a standard Gaussian lens, a microphoto lens dedicated to close-up photography equipped with an intermediate tube, a bellows, etc. There is.

When using a so-called single focal length photography system for close-up photography using bellows, etc., if you want to change the magnification and photograph the subject once it is in focus, The operator had to move the entire photographic system including the tripod, or move the photographic lens and camera on the bellows rail to change the object-to-image distance, and then refocus, which was a very troublesome operation.

On the other hand, if you use a variable focal length zoom lens,
Such operational troubles are eliminated.

An example of a zoom lens that is used while maintaining a constant distance between objects and images is a zoom lens for copying machines. This zoom lens for copying machines is mainly used for photographing at same magnification, and the photographing magnification range is limited to an extremely narrow range. In addition, in terms of aberrations, various aberrations such as distortion are relatively well corrected in the same magnification state, or many aberrations occur on the low magnification side and the high magnification side outside of the equidistant position.

In U.S. Pat. No. 3,905,685, from the object side, positive refractive power, negative refractive power, and first refractive power of positive refractive power. Second. We have proposed a zoom lens consisting of three lens groups, a third group, in which the first and third groups are moved symmetrically with respect to the second group during zooming, and the entire lens system is moved. In this zoom lens, since the first group and the third group are composed of one positive lens, there are relatively many aberration fluctuations due to zooming. Also, the F number when converted to infinity is relatively dark at F5.6, for example 35mm-
For reflex cameras, there were problems such as the matte surface of the finder being dark and making focusing difficult.

(Problems to be Solved by the Invention) The present invention aims to simplify the operational troubles during close-up photography, and by changing the photographing magnification while maintaining the distance between objects constant, for example, photographing magnification. The purpose of the present invention is to provide a bright finite-distance zoom lens with an F number of about 4, which has high optical performance and satisfactorily corrects aberrations over a wide imaging magnification range of 0.4 to 2.5 times.

(Means for solving the problem) From the object side, the first group has positive refractive power, and the second group has negative refractive power.
It has three lens groups: a group and a third group with positive refractive power;
When the first group and the third group are moved symmetrically with respect to the second group on the optical axis and the entire system is moved integrally on the optical axis to perform magnification while keeping the object-image distance constant. , 0.75< Fl/F <0.85 - (1
).

(Example) FIGS. 1 and 2 are cross-sectional views of a lens according to a numerical example 1°2 of the present invention.

In the figure, symbol 1 is the first group with positive refractive power, ■ is the second group with negative refractive power, and ■ is the third group with positive refractive power.

In this example, both the first and third lens groups are replaced by the 21st lens group.
The system is moved symmetrically on the optical axis as shown by the arrow with respect to #, and the entire system is moved integrally on the optical axis to change the magnification from low magnification to high magnification while keeping the distance between the object and image constant. ing.

In this embodiment, when the imaging magnification is 1x, the 1st and 3rd groups are farthest from the 2nd group, and as the imaging magnification changes from 1x to low magnification or to high magnification, the 1st and 3rd groups are The magnification is changed so as to approach the second group symmetrically.

And the first. The refractive power of the second group is determined by the above-mentioned conditional expression (1),
By specifying so as to satisfy (2), various aberrations that occur during close-up photography can be well corrected, and high optical performance can be obtained over a wide range of photographic magnifications.

In close-up photography using a general photography system, spherical aberration and field curvature become undervalued as the magnification increases from low to high.

In addition, along with this, axial chromatic aberration and lateral chromatic aberration worsen, furthermore, outward coma aberration occurs more frequently, and the overall image quality deteriorates significantly.

If the lens system is configured symmetrically, distortion, chromatic aberration of magnification, coma, etc. can be reduced to zero in principle in the same magnification state.

However, when the lens system is made symmetrical, the degree of freedom in correcting aberrations is lost, and many aberrations occur on the low and high magnification sides of the same magnification, making it difficult to correct these well. come. In particular, when the photographing magnification is greater than about 2 times, spherical aberration and curvature of field increase in the negative direction, and a large amount of outward coma aberration occurs, causing a significant deterioration in the image quality of the entire screen.

In contrast, in the present invention, the lens system is composed of three lens groups having a predetermined refractive power, the entire lens structure is actively made asymmetrical, and the refractive power of each lens group is specified as described above. This provides excellent aberration correction over a wide photographic magnification range from the low magnification side to the high magnification side, including the same magnification.

Next, each of the above-mentioned conditional expressions will be explained.

Conditional expression (+) relates to the refractive power of the first group, and is intended to favorably correct various aberrations while downsizing the entire lens system.

If the lower limit of conditional expression (1) is exceeded and the refractive power of the first group becomes too strong, the amount of movement relative to the second group to obtain the desired photographic magnification decreases, and the overall length of the lens becomes short. However, fluctuations in aberrations increase with zooming, and in particular spherical aberrations become insufficiently corrected, and distortion also increases beyond the same magnification. Furthermore, assembly precision becomes more difficult. In addition, the object-image distance becomes shorter, and as a result, the working distance at higher magnifications becomes too short, making it difficult to illuminate the object effectively, for example.

If the upper limit of conditional expression (1) is exceeded and the refractive power of the first group becomes too weak, the amount of movement relative to the second group to obtain the desired photographic magnification will increase, and both the overall length of the lens and the diameter of the front lens will become large. It's starting to change. This is not good because the lens groups tend to interfere with each other on the low or high magnification side.

In addition, in the case of a mechanical configuration in which a cam groove is cut in the cam ring and the lens group is moved by rotating the cam ring, the amount of lens movement relative to the rotation angle becomes large, making it difficult to smoothly change the magnification.

Conditional expression (2) concerns the refractive power of the second group, and together with conditional expression (1), maintains a good balance in the refractive power of the entire system, obtains high optical performance over the entire zoom range, and reduces the amount of movement of the entire lens system. The purpose is to regulate the

If the lower limit of conditional expression (2) is exceeded and the negative refractive power of the second group becomes too strong, the amount of movement of the entire lens system to obtain the desired photographic magnification will decrease, but various aberrations due to zooming will increase. There will be more fluctuations.

Furthermore, if the upper limit of conditional expression (2) is exceeded and the negative refractive power of the second group becomes too weak, the amount of movement of the entire lens system due to zooming will increase, and the object-image distance will decrease. . As a result, the working distance becomes too short on the high magnification side, causing the same problem as described above.

In addition, when used in combination with a bellows, problems arise such as the back focus must be extended by the amount that the bellows is inserted between the lens and the camera.

The finite distance zoom lens, which is the object of the present invention, can be achieved by satisfying the above conditions, but in order to obtain good optical performance over the entire zoom range, it is preferable to satisfy the following conditions.

The first lens group has a twelfth lens in which the lens surface on the image side is concave toward the image surface and the negative eleventh lens surface is convex, and the third lens group has both lens surfaces convex. The 31st lens has a negative lens whose object-side lens surface has a concave surface facing the object side, and the radius of curvature Ri of the j-th lens surface of the first group is
When j is 0.7 < R1,2/R1,3 <0.9・---
------(3) 0.87<|R3,3,3/R3,2|<0.97゜(
R3,3<0, R3,2<0)・・・・・・・−(
4) Satisfy the following conditions.

Conditional expressions (3) and (4) appropriately set the shape of the air lens formed by the two lenses when the first and second groups are composed of two lenses with a predetermined shape, and mainly take into account spherical aberration. This is to properly correct the

If the lower limits of conditional expressions (3) and (4) are exceeded, the divergence of the lens surfaces (R1, 2; R3, 2) with negative refractive power becomes too strong, and the overcorrected spherical aberration is replaced by a lens with positive refractive power. It becomes difficult to correct it on the surface.

On the other hand, if the upper limit of conditional expression (3) is exceeded, the divergence of the lens surface with negative refractive power becomes too weak and spherical aberration tends to be under-corrected, which is not good.

In addition, in the present invention, in order to correct aberrations, it is preferable that the second lens group has a positive meniscus-like second lens with a convex surface facing the object side, a 22nd lens in which a positive lens and a negative lens are bonded together, an aperture, a negative lens and a positive lens. It is preferable that the lens be composed of a 23rd lens which is a 23rd lens bonded together, and a 24th lens that has a positive meniscus shape with its convex surface facing the image plane side.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

Numerical Example l R1-1 1302.30 R2-42,14 R3-48,09 R4--59,83 R5-21,40 86-48,51 R7--60,66 R8--30,15 R9- 24,92 RIO-Aperture R11--36,92 Ri2- 48.87 Ri3- 142.79 R14--53,68 Ri5--25.73 RIO-85,7O R+7--42.99 RIg--39, 81 R19-242,80 Dll D 4 dance D 5 earthquake D 8 fable DI3- N l-1.68893 1- 31.1 N 2-1.77250 2- 49.6 N 3-1.72916 3- 54. 7 N 4-1.84666 ν 4- 23.98
5=1.56138 v 5- 45.2N
6-1.59270 ν 6- 35.
3N 7-1.72916 ν 7- 54.7
N 8-1.74320 8- 49.3 N 9-1.77250 9- 49.6 Nl (1-1.68893 vIO- 31.1 F - Fl/F = lF21/F: 97, 05 0, 82 1,75 R1,2 7R3.3 = 0.881 R3,3
/R3.2 1 = 0.98 Numerical Example 2 R 1-582.66 R2- 40.74 R3- 53.88 R 4- -42.29 85- 23.36 R6- 81.52 R 7- - 40.75 R8- -21.62 R9- 30.88 DI-1.6 02- 2.13 D3-10. O D4- Variable D5 Strict 2. O D B Seal 0.95 07@3.0 D 8 Self 3.0 D9-2. O N 1 1.68893 N 2-1.72916 N :l-1.7440O N4■1.78472 N 5-1.57041 ν l- 31.1 ν 2- 54.7 C 3- 44.8 ν 4- 25.7 Shi 5- 48.1 RIO- comparison R11- -39.48 Ri2- 20.95 Ri3- 54.46 Ri4 bite -57.88 R15- -2195 816- 82.30 R17- -: 14.85 R18- -31.93 R19-158.50 DIO-2. O Dll- 1.2 012 3.0 0+3- 0.72 014 dew 2.0 015- Variable 016- 10.0 017- 1.0 DI8- 2.51 N 6=1.59270 v l- 35. 3
N 7-1.729]6 ν 7- 54.7N
8 Sodium 1.62041 8- 60.3 N 9-1.77250 9- 49.6 N10-1.69895 υ10- 30.1 F = 88.29 R1,2 /R1,3
= 0.76Fl/F =0.7931R3
,3/R3,2+=0.921 F2 1/F=2
．． 265 (Effects of the Invention) According to the present invention, the entire lens system is composed of three lens groups having a predetermined refractive power, and the refractive power of each lens group is set as described above, thereby eliminating operational trouble during close-up photography. A finite-distance zoom lens with high optical performance that achieves good aberration correction within the imaging magnification range of 0.4 to 2.5 degrees while maintaining a constant object-to-image distance. can be achieved.

[Brief explanation of the drawing]

1st. FIG. 2 is a cross-sectional view of the lens of Numerical Example 1.2 of the present invention, and FIG. FIG. 4 is a diagram showing various aberrations of Numerical Example 1.2 of the present invention. In the aberration diagram (^). In (B) and (C), the imaging magnification is 0.4x, 1x,
This is when it is 2.5 times larger. In the figure, I, Il, and III are respectively 1st. Second. 3rd group,
Arrows indicate the direction of movement of the lens group during zooming. ΔM is the meridional image plane, ΔS is the sagittal image plane, d is the d-line, g
is the g-line, and S and C are sine conditions. Figure (''A) (B) Figure (C) Figure (△) Figure (B) Distortion convergence (Z)

Claims (1)

Claims: (1) It has three lens groups, in order from the object side: a first group with positive refractive power, a second group with negative refractive power, and a third group with positive refractive power; The first and third groups are moved symmetrically with respect to the second group on the optical axis, and the entire system is moved integrally on the optical axis to maintain a constant object-image distance while changing magnification. When the magnification is the same, the focal length of the entire system is F, and the focal length of the i-th group is F.
A finite distance zoom lens, characterized in that it satisfies the following conditions: 0.75<F1/F<0.85 1.5<|F2|/F<2.5, (F2<0), where i is 0.75<|F2|/F<2.5. (2) The first group includes a negative eleventh lens whose lens surface on the image plane side is concave toward the image plane side, and a twelfth lens whose both lens surfaces are convex. It has a 31st lens with a convex lens surface and a negative lens with a concave surface facing the object side, and when the radius of curvature of the j-th lens surface of the i-th group is Ri,j 0.7<R1, 2/R1, 3<0.9 0.87<|R3, 3/R3, 2|<0.97, (R3
, 3<0, R3, 2<0) The finite distance zoom lens according to claim 1, wherein the zoom lens satisfies the following conditions.