JPS63285510A - Zoom lens - Google Patents

Abstract

PURPOSE:To compensate aberrations resulting from a large aperture ratio and a high magnification ratio excellently by providing 1st-5th lens group I-V and satisfying inequalities for the image formation magnification and incidence positions of the 2nd and 3rd groups II and III and the lens constitution of the 2nd group. CONSTITUTION:The 1st-5th lens group I-V are provided and the 2nd group II has three lenses; and the inequalities hold for the Abbe number vi.j of glass of the (j)th lens ij in the (i)th group, the focal length Fi of the (i)th group, the focal length Fw of the whole system on a wide-angle end, the image formation power values beta2T and beta3T of the 2nd and 3rd groups II and III on a telephoto end, the magnification variation ratio Z, and the distance I from the 1st lens surface of an entrance pupil on the wide angle. Thus, the inequalities are satisfied as to the image formation magnification values of the 2nd and 3rd groups and the lens constitution of the 2nd group to compensate the aberrations resulting from the large aperture ratio and high magnification variation ratio excellently, thereby obtaining the excellent optical performance over the entire magnification variation range.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a zoom lens, and in particular to a photographic camera or video camera that has a large aperture with an aperture ratio of about 1.4 and has good optical performance over the entire zoom range. The present invention relates to a compact zoom lens with a short overall lens length suitable for cameras and the like.

(Prior Art) Photographic cameras, video cameras, and the like have traditionally required compact zoom lenses with large apertures, high zoom ratios, and high optical performance.

Among these, video cameras require a zoom lens with as large an aperture ratio as possible because the imaging device has relatively low sensitivity.

Currently, 3-inch tubes are often used as image pickup tubes for video cameras due to two reasons: compactness and image quality. Also, 8mm video cameras are increasingly being used because they are easier to operate and can be made more compact. The image pickup tubes used in these devices are required to be further downsized while maintaining good image quality, and inch tubes and inch image pickup plates have recently been adopted.

A zoom lens with an aperture ratio of about 1.2 to 1.4 and a variable ratio of about 6 is disclosed in, for example, Japanese Patent Laid-Open No. 60-51813 and Japanese Patent Laid-Open No. 60-60.
It has been proposed in Publication No.-260912 and the like. The publication describes, in order from the object side, a first group with positive refractive power for focusing, a second group with negative refractive power for zooming, a third group for correcting the image plane that changes due to zooming, and a second group with negative refractive power for zooming. We have proposed a so-called five-group zoom lens having five lens groups: a fourth group for converting the light beam from the third group into an afocal light beam, and a fifth group for imaging.

Generally, in order to shorten the overall length of a lens, it is effective to downsize the first group on the object side, and for this purpose, it is sufficient to increase the FNo. This is not very desirable for video cameras and the like that require a lens system. In general, in order to reduce the FN and downsize the entire lens system, it is important to appropriately set the number of optical chambers in each lens group that constitutes the lens system.

If you try to make the entire lens system smaller and have a larger aperture ratio by simply strengthening the refractive power of each lens group, many higher-order aberrations will occur, such as spherical aberration at the center of the screen, coma aberration toward the periphery of the screen, and sagittal halo aberration. However, it becomes difficult to obtain high optical performance.

For example, if you try to increase the refractive power of the first group on the object side and make it more compact, you will have to increase the overall imaging magnification from the variable magnification section to the imaging section, and as a result, the Aberrations occur, manufacturing errors become severe, and it becomes difficult to obtain a predetermined optical performance.

In particular, when using an inch-sized image sensor, the effective screen diameter is φ
6, the total length of the lens from the first lens surface to the image forming surface is L = about 12.5φA to 14φ4, which means that the total lens length is relatively long, and the total length of the lens can be reduced while maintaining good optical performance. It comes with a length that is difficult to shorten.

(Problems to be Solved by the Invention) The present invention has an aperture ratio of about F1.4, a variable power ratio of about 6, a standard angle of view at the wide-angle end, and moreover, it is possible to reduce the size of the entire lens system. The purpose of the present invention is to provide a zoom lens that exhibits high optical performance over a variable power range.

(Means for solving the problem) From the object side, the first group has positive refractive power for focusing, the second group has negative refractive power and has a variable magnification function, and corrects the image plane that changes due to variable magnification. There are five lens groups: a third group with a negative refractive power to convert the divergent light beam from the third group into a substantially parallel light beam, a fourth group with a positive refractive power to turn the divergent light beam from the third group into a substantially parallel light beam, and a fifth group which has an imaging function. The second group has a negative meniscus-like second group with a convex surface facing the object side.
It has three lenses: a 22nd lens with a concave lens surface, and a positive 23rd lens with a convex surface facing the object side, and the Atsube number of the glass of the j-th 22nd lens in the i-th group is ν8. ．． J, the focal length of the i-th group is Fl, the focal length of the entire system at the wide-angle end is Fw, the second and third groups at the telephoto end
When the imaging magnification of each group is β2〒 and β〒, the variable power ratio is 2, and the distance of the entrance pupil from the first lens surface at the wide-angle end is 1, then 1.0<lFz/FwI<
1.2 ””(1) 1.05< I β
zd/f-? <1.2-
--・-(2) 0.17< 83r/ J-1
7< 0.23 = (3) 2.3< l
/ F, < 2.6
--------(4)53<(C2I+C22)/2
・・・・・・(5)v2. j< 26
...-(6) must be satisfied.

(Example) FIG. 17 is a sectional view of a lens of Numerical Example 1 of the present invention. The figure in the figure shows the first group with positive refractive power for focusing, ■ the second group with negative refractive power for zooming, and ■ the negative refractor to correct the image plane that changes with zooming. The third group has a strong power, ■ is the fourth group with positive refractive power to produce a diverging light beam from the third group and is almost parallel, ■ is the fifth group with a fixed imaging function, and SP is a fixed aperture. It is.

In this embodiment, in such a zoom type, the second group,
By setting the imaging magnification of the third group, the entrance pupil position, and the lens configuration of the third group to satisfy the above-mentioned conditional expressions (1) to (6), it is possible to correct aberrations associated with a large aperture ratio and a high zoom ratio. It performed well and obtained good optical performance over the entire zoom range.

In particular, residual aberrations in the variable power system, such as spherical aberration and comatic aberration, are corrected in a well-balanced manner while shortening the overall lens length.

Next, the technical meaning of each of the above conditional expressions will be explained.

Conditional expression (1) relates to the negative refractive power of the second group, and is intended to easily obtain a predetermined zoom ratio while reducing aberration fluctuations during zooming. If the lower limit value is exceeded and the refractive power becomes too strong, the amount of movement of the second lens group during zooming will decrease, but aberration fluctuations will increase and it will become difficult to correct them. Moreover, if the refractive power becomes too weak by exceeding the upper limit value, the amount of movement of the second group to obtain a predetermined variable power ratio increases, which is not good because the total length of the l/lens increases.

Conditional expressions (2) and (3) are related to the ratio of the imaging magnification of the second group and the third group at the telephoto end to the valley zoom ratio, and are mainly aimed at reducing the size of the entire lens system while ensuring a predetermined variable power ratio. This is for the purpose of achieving this.

If the lower limit of conditional expression (2) is exceeded and the imaging magnification of the second group becomes too small, the distance between the second and third groups at the wide-angle end increases, increasing the lens diameter of the first group for focusing. Otherwise, it will be difficult to secure a predetermined amount of light at the periphery of the screen, and if the imaging magnification of the second group exceeds the upper limit and becomes too large, interference between the second and third groups during zooming will occur. In order to avoid this, it is necessary to widen the distance between the second and third groups at the telephoto end, which is not a good idea because the overall length of the lens increases.

If the lower limit of conditional expression (3) is exceeded and the imaging magnification of the third group becomes too small, the negative refractive power of the third group becomes strong, and as a result, the degree of divergence of the luminous flux from the third group increases. As the distance increases, the outer diameter of the lens of the subsequent fourth group increases. On the other hand, if the imaging magnification of the third group exceeds the upper limit and becomes too large, the negative refractive power of the third group becomes weak, the amount of movement of the third group increases during zooming, and the overall lens length increases accordingly. is increasing.

Conditional expression (4) concerns the entrance pupil position at the wide-angle end, that is, the distance of the entrance pupil from the first lens surface, and mainly prevents aberration fluctuations during focusing while preventing an increase in the lens diameter of the first group. This is to reduce it.

Generally, the shorter the entrance pupil position is, the lower the height of incidence of the off-axis light beam on the first lens surface, and the smaller the lens diameter of the first group. However, as the lens diameter of the rear lens group increases, it becomes difficult to maintain the optical performance of the entire screen in a well-balanced manner. Conditional expression (4) was set taking these points into consideration; if the lower limit value is exceeded and the entrance pupil position becomes too short, the positive refractive power of the first group must be increased, and the focus will be affected. The actual aberration fluctuations will increase.

Also, if the entrance pupil position becomes longer than the upper limit, the first
This is not good because the lens diameter of the group increases.

Conditional expressions (5) and (6) are related to the Atsube numbers of the three lenses that make up the second group, and are mainly intended to reduce chromatic aberration fluctuations during zooming. If the value is outside the range, chromatic aberrations, especially lateral chromatic aberrations, will fluctuate more during zooming, and it will become difficult to correct this well.

The zoom lens that is the object of the present invention is achieved by satisfying the following two conditions, but in order to achieve even better aberration correction, the fourth and fifth groups should be configured as follows. It's good to do that.

The fourth lens group has a positive fourth lens with a strong refractive surface facing the image side, and the fifth lens group has a positive fourth lens with a strong refractive surface facing the object side, and both lens surfaces are convex, starting from the object side. 5 lenses, a negative meniscus-shaped 52nd lens with a concave surface facing the object side, a positive 53rd lens with a strong refractive surface facing the object side, a negative meniscus-shaped 54th lens with a convex surface facing the object side, It may be configured to have six lenses: a 55th lens whose both lens surfaces are convex with a strong refractive surface facing the image plane side, and a positive 56th lens with a strong refractive surface facing the object side.

It should be noted that a refractive surface having a strong refractive power on the image plane side is defined as compared to the refractive power of the other surface, that is, the lens surface on the object side. The same is true for refractive surfaces that are strong on the object side. By configuring the fourth and fifth groups in this manner, residual aberrations in the variable power system, such as spherical aberration and introverted coma toward the periphery of the screen, can be corrected in a well-balanced manner as a whole.

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. R28 and R29 are face plates, filters, etc.

Further, Table 1 shows the relationship between each of the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical example! ? I ~5.5 FNo-1:1.4 2ω-47
, 6' to 9. l'ro l= 7.756
D I-0,134N I”1.80518 v
l-25,412= 3.442 D 2-
0.59] N2-Il, 51633 v2-6
4. IR3--9,531D 3 rumors 0.0+604
- 2.76: l D 4- 0.386
8 3-1. [10311v 3-60.7R5
= 11.218 05- Variable R6 = 14.
307 D fi = 0.086 N
4-1.71300 v 4-53.8R7-1
,2+5 D7- 0.312R8=-1
,63108-0,086N 51-1.71300
v 5-53.8R9-1,63109=0.257
NB-1,84666v 8-2:1.9 old 0-
-82.089 DIO-variable old 1 = -2,37
3DI+-0,096N 7-1.71300v
7-153.8 old 2--14.802 Di2-
Variable RI3- 12.778 DI3= 0.41
9 N 8-1.89680 v 8-55.5RI
4- -2.092 014-0.107R15-Aperture DI5~0.214 RI6- 3.733 016-0.333 N 9
”1.65844 v 9-50.98I7- -7.
603 017-0.144R18s -2,384
Di8- 0.107 Nl0-1.80518
ν 1Os25.4R19--13,781019-
0,0161120= 3.2+6 D20= 0
．． 236 Ni1-1.65844 v If-50
,9R21-26,338021-1,719R22=
9.547 022-0.088 N+21-1
．． 80518 Shi12-25.4R23-1,9090
23-0,065R24=3.035D24-
0.333 Nl3-1.56384 v 13-6
0.7R25--3,035D25-0.016826
= 2.109 026- 0.300
N14-1.51742 u14-52.4R27-
-11,863027-0,429828-cD
D28- 0.591 N15-1.51633
v15-64. lR29 layer ω Numerical Example 2 F=1 to 5.6 FNo-1: 1.4 2ω= 4
7.6' ~ 9.1'Rl-8,401D I-0,1
34N I-1,805+8ν l-25,4R2-3
,50202=0.612 82-1.51633
v 2-64. IR3--7,357D 3-0.
016R4-2,552D 4-0.397 N 3
-1.60311 v 3-60.715- 7.03
8 D 51- Variable R6 = 10.093 06
-0.086 N 4-1.7+300 v 4-5
3.8R7■ 1.206 D 7- 0.
29908--1.50308-0.086NS=1.
71300v5-53.889- 1.503 D
9-0. 306 N 6-1.80518 Jiro 25
．． 4nlO--18,283010-variable old 1=-2,722DI+-0,096N 7"1
．． 71300 v 7-53.8RI2・-68,68
2[112= variable RI3- 22.343 013-
0.387 N 8-1.71300 v 8-53
．． 8Rth--2,035014-0,107R15-compared to 015-0.215 Old 6 = 5.610 Di6- 〇, 290
N 9-1.65844 v 9-50.
91 (17 praise -6,537017-0,176111
8-1-2, 0:10 018-0.107 Nl0
-1.80518 vlO-125,4RI9- -
5.427 019-0.016R20-3,119
020-0,268N11-1.63854 Shi I+
-55.4R21--20,632D2+-1,397
R22-5,421D22- 0.086 Nl2
=1.80518 v 12-25.41123
1.8+4 023maro 0. +15R24・4.
701 024= 0.311 Nl31-1.51
633 v13-64. lR25 Kurei -2,4350
25-0,0161126=2.992 0
26 = 0.279 N14 1.51633
v14=64.1027- -7.814 02
7-0.4301 (28-ω D28-0.59
1 Ni5-1.51633 C15-84. +
1 Demon 29- Oe) Numerical Example 3 F-i ~5.6 FNo-1: 1.4 2ω-
47,6'~9.1'RI=7.793D
I= 0.134 N l=1.80518 v 1
s25.4It 2- 3.503 D 2-0.5
69 N 2-1.51833 v 2-64.1R
3・-10,46:l D 3~0.01fiR4-
2, RO4D 4-0.197 N 3-1.80:
IIIv3-60.7B 5- 12.784 05-
Variable R6-10,092D 6-0.086N
4-1.71300shi 4-53.8R7-1,247
07-0,299 R8--1,632D 8 stories 0.086N5・1.71
300shi5-53.8R9I=! , 720 D 9s
0.268 N 6” 1.80518 v 6-25
．． 410-204.843 DIO-Variable RI+=
-2,609DI+-0,096N 7-1.7+3
00 Sheer 53.8RI2--33.052 012-
Variable 1 (13 things 22.168 013-0.387
N 8-1.71300shi 8-53゜8014-
-2.037 DI4- 0.1071 (+5-
Aperture DI5-0.215R16・4.745 0
16-0.268 N 9-1.65844 C9-5
0.91117--8.724 DI7-0.19
01118- -2.084 D18= 0.107
8IO-1,80518Z/10-25.4R1! l
--5,021019-0,016R20□ 3.1
34 020-0.268 8II=! ,63854
C1l-55.4R21--48, 809021-1,
397R22-5, 383D22-0.086 N+
2-1.805+8ν12-25.4R23-1,79
8D23-0.115R24=4.523D2
4-0.311 N+3-1.51633 v 13
-64. lR25--2,536025-0,016R
26-2,9+7 D26-0.279 NI4-
1.51633 v 14-64.1R27--6, f
i61 027-0.4301128-1 oo
D28- 0.591 N+5-1.51
633 v 15 = = 64.1 (Table 1) (Effects of the Invention) As described above, the present invention provides high optical performance with a large aperture ratio, high variable power ratio, and miniaturization of the entire lens system. A zoom lens suitable for photographic cameras and video cameras can be achieved.

In particular, in the present invention, the total length of the lens is L = 11.2φ6~1
A compact zoom lens as short as 1.6φ6 can be achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens according to Numerical Example 1 of the present invention, and FIGS. 2 to 4 are aberration diagrams of Numerical Examples 1 to 3 of the present invention, respectively. In the aberration diagrams, (^) is an aberration diagram at the wide-angle end, and (B) is an aberration diagram at the telephoto end. I, II, III, I in the diagram
V and V are respectively 1st. Second. Third. 4th and 5th groups, ΔM
is a meridional image plane, ΔS is a sagittal image plane, d is a d-line, g is a g-line, and SP is an aperture. Part F / 1.9 J゛24.55゜4
Figure (B) tJ = 4,550 u = 4,55'-'), I
JO, '), UU-0,0050,005 deku collection & za)
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Claims (2)

[Claims] (1) Starting from the object side, the first group has a positive refractive power for focusing, the second group has a negative refractive power and has a variable magnification function, and the second group has a negative refractive power to correct the image plane that changes due to the variable magnification. 3rd group, a 4th group with positive refractive power for converting the diverging light beam from the third group into a substantially parallel light beam;
The fifth lens group has five lens groups having an imaging function, and the second group includes a negative meniscus-shaped 21st lens with a convex surface facing the object side, a 22nd lens with both lens surfaces concave, and It has three lenses including a positive 23rd lens with a convex surface facing the object side, the Abbe number of the glass of the j-th lens of the i-th group is ν_i_,_j, and the focal length of the i-th group is F_i. , the focal length of the entire system at the wide-angle end is F_w, and the imaging magnification of the second group and the third group at the telephoto end are each β_2.
_T, β_3_T, the variable magnification ratio is z, and the distance of the entrance pupil from the first lens surface at the wide-angle end is l: 1.0<lF_2/F_wl<1.2 1.05<lβ_2_Tl/√z<1. 2 0.17<β_3_T/√z<0.23 2.3<1/F_w<2.6 53<(ν_2_1+ν_2_2)/2 ν_2_3<26 A zoom lens characterized by satisfying the following conditions.