JPS63247715A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a miniature zoom lens whose aberration is corrected satisfactorily, by allowing four lens groups having refracting powers of positive, negative, positive and positive in order from an object side, to satisfy prescribed conditions. CONSTITUTION:The titled zoom lens has four lens groups of the first group I of a positive refracting power for focusing, the second group II of a negative refracting power for moving monotonously at the time of variable power, the third group III of a positive refracting power for moving in the direction reverse to the moving direction of the second group II in order to maintain an image surface which is varied by following up variable power, in a prescribed position, and the fourth group IV of a positive refracting power for executing a fixed image forming action. Between the second group II and the third group III, a fixed diaphragm S.P is provided, the fourth group IV has the lens group of a negative refracting power and the lens group of a positive refracting power, the former lens group has a meniscus-like lens of a negative refracting power, whose concave surface is turned to the object side, the latter lens group has a lens of both lens surfaces, a meniscus-like lens of a negative refracting power whose convex surface is turned to the object side, and a lens whose both lens surfaces of convex surfaces, and they satisfy various conditions of the inequality I - the inequality IV.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens, and particularly to a zoom lens with high optical performance suitable for photographic cameras, video cameras, and the like.

(Prior Art) Photographic lenses used in photographic cameras, video cameras, etc. have traditionally been required to be bright and compact. Particularly in video cameras, since the image pickup device has relatively low sensitivity, it is required to be brighter than the F number of about 1.4. In addition, with the integration of the video recorder and the video camera, the shooting lens for a video camera must be smaller and lighter, a zoom lens with high optical performance, and the front of the image pickup device such as an image pickup tube or COD. It is required that there be a space of sufficient length for arranging various filters such as a protective glass, a stripe filter for color separation, and a low-pass filter, that is, a back focus of sufficient length.

As described above, there are various requirements for photographic lenses used in video cameras, and if these requirements are to be met, it becomes difficult to maintain good optical performance. In particular, it becomes difficult to satisfactorily correct various aberrations such as spherical aberration, coma aberration, and distortion, which results in a decrease in image contrast.

(Problems to be Solved by the Invention) The present invention is compact and has high optical performance suitable for photo cameras, video cameras, etc., which achieves good aberration correction while reducing the overall length and weight of the lens. The purpose is to provide zoom lenses.・(Means for solving the problem) Starting from the object side, the first group has positive refractive power for focusing, the second group has negative refractive power that moves monotonically when changing the magnification, and the second group changes as the magnification changes. In order to maintain the image plane at a constant position, a third group with a positive refractive power moves in the direction opposite to the moving direction of the second group, and a fourth group with a positive refractive power performs a fixed imaging function. A fixed aperture is provided between the second group and the third group, and the fourth group includes a 4-1 lens group with negative refractive power and a 4-1 lens group with positive refractive power. It has two lens groups of 2 lens groups, and the 4-1
The lens group consists of a meniscus-shaped 4th lens with a negative refractive power with a concave surface facing the object side, and the 4-2 lens group has a 4□1 lens with both lens surfaces convex, and the convex surface faces the object side. It has a 422nd lens in the form of a meniscus with negative refractive power and a 423rd lens in which both lens surfaces are convex, and the radius of curvature of the i-th lens surface counting from the object side of the fourth group is RI.
Vi, the i-th lens thickness or air interval is DIVi
, when the focal length of the entire system at the wide-angle end is fw, 0.
55<RrVI/RrV4<0.68-(1)
1.00<RIV6/fw<1.23...
・(2) 0, 51 <l RrV6 /RrV7 l
<0.66-(3)0, 2<DrV2/f
w<0. 3 --- (satisfying the following conditions.

(Example) FIG. 1 is a sectional view of a lens according to Numerical Example 1 of the present invention.

In the figure, I is the first group with positive refractive power for focusing, ■ is the second group with negative refractive power that moves monotonically toward the image plane when changing magnification, and ■ is the image plane that changes with changing magnification. The third group with positive refractive power moves in the opposite direction to the moving direction of the second group in order to maintain a constant position, ■ is the fourth group with positive refractive power that performs a fixed imaging function, and sp is the second group This is a fixed iris diaphragm placed between the second group and the third group.

In this embodiment, the diaphragm is placed between the second and third groups, that is, placed approximately in the middle of the optical system, thereby reducing the diameter of the front lens of the first group, making the entire lens system more compact. We are trying to make this happen.

In a typical zoom lens, the first group often accounts for 50 to 80% of the weight of the entire zoom lens. Therefore, in order to reduce the weight of a zoom lens, it is effective to reduce the specific gravity of the material of the first lens group or to reduce the volume by reducing the diameter of the front lens of the first group. Among these materials, it is difficult to select a material with a small specific gravity because it reduces the degree of freedom in optical design.

Therefore, in order to reduce the weight of the lens system while maintaining good optical performance, it is effective to reduce the diameter of the front lens in the first group.

For example, considering the volume of a lens proportionally, it is proportional to the cube of the lens diameter, so if the lens diameter can be reduced by 10%, the volume can be reduced from (0,9)3 to about 27%. In this embodiment, the diameter of the front lens of the first group is prioritized in order to reduce the weight of the entire lens system. In other words, priority is given to reducing the diameter of the front lens of the first group by arranging the diaphragm at a substantially intermediate position in the optical system between the second group, which is close to the first group, and the third lens group. In this embodiment, the diaphragm and lens are set so that both the diameter of the front lens of the first group determined by the oblique light beam on the wide-angle side and the diameter of the front lens of the first group determined by the axial light beam on the telephoto side are small. The group is arranged.

In addition, the fourth group is divided into two lens groups, the 4-1st lens group and the 4-2nd lens group, with the widest air gap as the boundary, and the 4th to 1st lens groups have negative refractive power, and the 4-2nd lens has negative refractive power. By setting the groups to have positive refractive power and setting the lens shape and lens thickness of each lens group to satisfy Moe's conditional expression, excellent aberration correction is achieved over the entire zoom range. .

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

Conditional expression (1) relates to the ratio of the radius of curvature of the object-side lens surface of the 411th lens to the image-side lens surface of the 42nd lens, that is, the refractive power ratio, and mainly relates to the refractive power ratio of the object-side lens surface of the 411th lens. This is for correcting spherical aberration and coma aberration generated on the 42nd lens surface in a well-balanced manner on the image side of the lens. If the upper limit is exceeded, spherical aberration will be under-corrected and a lot of introverted coma will occur, and if the lower limit is exceeded, the spherical aberration will be over-corrected and a lot of outward coma will occur, which is not good.

Conditional expression (2) relates to the negative refractive power lens surface of the image plane flu of the 422nd lens, and aims to reduce the size of the entire lens system while mainly correcting distortion well, and further secures a sufficient back focus. It is for. If the upper limit is exceeded, a lot of barrel-shaped distortion will occur at the wide-angle end, and if the lower limit is exceeded, a lot of pincushion-shaped distortion will occur at the telephoto end, and it will be difficult to secure sufficient back focus. It's coming.

Conditional expression (3) is related to the ratio of the radius of curvature of the lens surface on the image side of the 4th □2 lens and the lens surface on the object side of the 423rd lens, and is mainly used to correct coma and astigmatism in a well-balanced manner. It is something.

If the upper limit value is exceeded, a large amount of comatic aberration will occur, and if the lower limit value is exceeded, astigmatism will deteriorate, making it difficult to correct these various aberrations in a well-balanced manner.

Conditional expression (4) is to appropriately set the air distance between the 4th □ lens and the 4th □ lens, that is, the air distance between the 4-1 lens group and the 4-2 lens group, and to balance distortion aberration. This is for correction. If the upper limit is exceeded, a lot of pincushion distortion will occur at the telephoto end, and if it exceeds the lower limit, a lot of barrel-shaped distortion will occur at the wide-angle end, which is not good.

Next, numerical examples of the present invention will be shown. In numerical examples R
r is the radius of curvature of the first lens surface from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and vi are numbers corresponding to the refractive index of the glass of the first lens in order from the object side.

Note that R25 and R26 are optical members such as a face plate and a filter. Table 1 shows the relationship between each of the conditional expressions described above and the count values in the numerical examples.

-: One numerical example I F-1 to 2.85 FNol: 1.40 to 1.65
2ω-49.4'~18.3' R1-29,082D I-0,1:l N +-1,
805+8ν 1-25.4R2-11,692D 2
-Q, 48 N 2-1.51633ν 2-64,
IR3--4,7790:]-0,02 R4-2,350D 4-0.32 N 3-1. ．． 6
5844ν 3・50.9R5-6,408D 5-variable R6-10,19706-0,11N 4-1.7+3
00ν 4-53.8R7-1,57207-0,25 R8--3,235D 8・0.10 N 5-1.5
1633ν 5-64, IRQ=1.752
D 9IIO, 25N 6-1.84666 v
6-23.9RIO-4,391DIO・Variable 1111・Aperture I)I+・Variable R12-87,710DI2-0.1787-1.66
672υ7-18.3RI3--4.001 DI3
-0.02RI4- 2.737 D eye -0.47N
8-1.71:100υ 8-53.8RI5--2
．． 136 015-0.11 N 9-1.84666
υ 9-23.9R111i~13. I64 DI8
=Variable RI7=-1,561DI7-0.1. IN
l0-1.60311 v lo-60,7R18--
3,526DI8-0.23R19-6,402019
-0,36Ni1-1.66672 Si11-48.
3R20--2.515 020-0.02 -1i
121- 1.772 021-0.11 N12
-1.84666 Shi12-23.9R22-1,1
17022-0,15 R23-1,941023-0,32N13-1.69
680 Shi13-55.5R24-18,99202
4-0,23R25-ω D25-0.63 N+4
-1.51633shi14-64. lR26 dew ω Numerical example 2 F snow 1~2.85 FNo-1: 1.40~l, 6
52ω-49,4°~18.3°Rl-46,959D I proverb 0.13 N I kick 1.805+8 ν 1-25.4R2-7,86
7D 2 0.49 N 2~1.51633υ2-6
4. IR3--4,77703-0,02 R4 2.296 D 4 servings 0.30 N
3-1.65844 υ 3-50.9R5-6
,09905-Variable R6--8,14406-0,11N 4-1.7+3
00shi 4-53.8R7-1,515D 7-0.23 118--4.319 08-0.10 N 5-1.
51633ν 5-64.1R9 Snow 1.517 D
9-0.28 N 6■1.84666shi6den23.
9RIO-3, 697010=Variable R11-Aperture Dll-Variable old 2-271.004 DI2-0.17 N 7-
1.66672υ7-48.3R13~-4,0600
13-0,02R14■ 2.661 [114 fog 0
．． 46 N 8-1.71300shi 8-53.8RI5
- -2.297 Old 5 0.11 N 9 Dew 1.84666 ν 9-23.9 Old 6-19.74
2 016-Variable R17--1,570017-0,11N10-1.6
0311 shi 10 覅60.7R18 禦 -3,412 DI
8-piece 0.23R19-6,398DI9-0.33
Nl1=1.66672 v 11-48.3R20
■ -2,549020-0,02R21-1,811
021 proverb 0.11 N+2 meals 1.84666 ν
12 Maro 23.9R22-1, 118D22-0.14 R23-1, 858023-0, 28N13-1.69
680 shi13-55.5n24-27.484
D24-0.23R25-■ 025-0.
63 N14 1.51633 し14■64. l
R26-ω Numerical Example 3 F-1 to 2.85 FNo=l: 1.40
~1.652ω-49.4'~18.3' R1 proverb-31,027D I-0,13N I wealth 1
．． 80518 ν 1-25.4R2-11,90
102-0,47N 2-1.51633ν 2-64
, IR3-1,81703-0,02 R4-2,37504-0,32N 3-1.6584
4ν 3-50.9R5-6,552D 5-Variable R6-10,850D B-0,11N 4■1.
7+300 ν 4 san 53.8117- 1.628
07-0.24R8--3,26608-0,108
5-1, 51633shi 5-64. IRQ-1,740D
9-0.25 N 6 Maro 1.84666 ν
6 So 23.9RIO-3,963010-Variable R11-Aperture Dll-Variable II2-71.354 012-0.17 N 7-1
．． 66672 sear 48.3r113--3.997
013-0.02 -Old 4- 2.728 0+4 Proverbs 0
．． 47 N 8-1.7+300shi8 53.8R15
--2,119015-0,11N 9-1.8466
6shi9-23.9 old 6-12.916 DI6-variable R17--1,564D17=O,II Nl0=1.
69680 v l0=55.5R18--3,457
DI8-0.231119- 6.393 DI
9-0.36 N11-1.70+54 ν 11
-41.2R20--2,508020-0,0211
21= 1.772 021-0.11 N1
2-1.84666 v 12-23.91122-
1.1+8 D22-0.16R23-1,9
50023-0,32N+3-1.71300 Si I
:l-53.8R24-25.188 024-0.
23R25I-oo D25-0.83
Nth = 1.51633 v 14-64. lR26I
-(1) (Table-1) (Effects of the Invention) As described above, according to the present invention, a variable power zoom lens consisting of four lens groups in which a fixed aperture is disposed between the second and third groups. By setting the lens configuration of the medium-fixed fourth group as described above, it is possible to achieve a zoom lens suitable for photo cameras, video cameras, etc., which has high optical performance and is designed to reduce the size of the entire lens system. .

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a lens of Numerical Example 1 of the present invention, and FIGS. 2, 3, and 4 are Numerical Examples 1, 2.3 of the present invention, respectively.
It is a diagram of various aberrations. In the aberration diagram (8), (II
) and (C) are aberrations at the wide-angle end, middle, and telephoto end, respectively. In the figure, I, U, III, and IV are the first,
Second. Third. The arrows in the fourth group indicate the locus of movement of each lens group during zooming from the wide-angle end to the telephoto end. Patent applicant Canon Co., Ltd. Kabuto 1 mouth

Claims (1)

[Claims] In order from the object side, a first group with a positive refractive power for focusing, a second group with a negative refractive power that moves monotonically when changing magnification, and a fixed position of the image plane that changes with changing the magnification. In order to maintain the image quality, it has four lens groups: a third group with a positive refractive power that moves in the opposite direction to the moving direction of the second group, and a fourth group with a positive refractive power that performs a fixed image forming function. A fixed aperture is provided between the second group and the third group, and the fourth group includes a 4-1 lens group with a negative refractive power and a 4-2 lens group with a positive refractive power. The 4-1 lens group has two lens groups.
The lens group is a meniscus-shaped 4_1_1 lens with a negative refractive power with a concave surface facing the object side, and the 4-2 lens group is a 4_2_1 lens with both lens surfaces convex, and a negative refractive lens with a convex surface facing the object side. It has a 4_2_2 lens with a force meniscus shape and a 4_2_3 lens with both lens surfaces being convex, and the radius of curvature of the i-th lens surface counting from the object side of the fourth group is RIVi, and the radius of curvature of the i-th lens surface is RIVi. DIVi the lens thickness or air spacing
, where fw is the focal length of the entire system at the wide-angle end, 0.55<RIV1/RIV4<0.68 1.00<RIV6/fw<1.23 0.51<|RIV6/RIV7|<0.66 0 A zoom lens that satisfies the following condition: .2<DIV2/fw<0.3.