JPS638620A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain the titled zoom lens small in size, and also, has a high optical performance by satisfying specific conditions among radius of curvature of the surface of i-th lens counted from the object side of a fourth group lens, the i-th lens thickness or air interval, and a focal distance of the whole system in the wide-angle end. CONSTITUTION:The titled zoom lens has a first group having positive refractive power for focusing, a second group having negative refractive power, which moves monotonously at the time of variable power, the third group having positive refractive power which moves so as to have a projecting locus in an image surface side in order to maintain the image surface varied by variable power, in a prescribed position, and the fourth group having positive refractive power, which executes a fixed image forming action, in order from an object side. Also, when a radius of curvature of the i-th lens surface counted from an object side of the fourth group lens, the i-th lens thickness or air interval, and a focal distance of the whole system in the wide-angle end are denoted as RIVi, DIVi, and fw, respectively, conditions of the expressions are satisfied.

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 focal length of sufficient length. .

As described above, various requirements are required of photographic lenses used in video cameras, and it becomes difficult to maintain good optical performance when trying to satisfy these requirements. 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 provides a compact zoom lens with high optical performance suitable for photographic cameras, video cameras, etc., which shortens the overall length of the lens and performs good aberration correction. For the purpose of providing.

(Means for solving the problem) In order from the object side, the first group has a positive refractive power for focusing, the second group has a negative refractive power that moves monotonically when changing magnification, and the image changes as the magnification changes. There are four groups: a third group with positive refractive power that moves with a convex locus toward the image plane in order to maintain the surface at a constant position, and a fourth group with positive refractive power that performs a fixed imaging action. The fourth group has a fixed diaphragm between the second group and the third group, and the fourth group has a 4-1 lens group with positive refractive power as well as a 4-1 lens group with positive refractive power. The 4-1st lens group has a positive refractive power that has stronger refractive power on the object side than on the image side.
The 4th-2nd lens group includes a meniscus-shaped 421st lens with a negative refractive power and a convex surface facing the object side.
It has a 422nd lens whose both lens surfaces are convex, and a 423rd lens with a positive refractive power that has stronger refractive power on the object side than on the image side, and the i-th lens counting from the object side of the fourth group.
When the radius of curvature of the th lens surface is RrVi, the thickness or air gap of the ith lens is Drvi, and the focal length of the entire system at the wide-angle end is f, 1.8 < RT.
V2 /RIV3 < 2.1 ・・・・・・
... (1) 2.7 kuIR■3/fw1ku3.3...
...(2) 0.03<DIV2/fw<0.04
・・・・・・(3) 0.06 < D ■6 / f
, < 0.09 ...- (4) 1.5 IR■6/fw1 1.8 (5) 0.
9 < R ■ 6 / R ■ g < 1.
1. The following condition (6) must be satisfied.

(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, the first group has a positive refractive power for focusing, and the second group has a negative refractive power, which moves monotonically toward the image plane during zooming.
In detail, ■ is the third group with positive refractive power that moves along the optical axis while having a convex locus on the image surface side in order to maintain the image plane in a constant position as it changes with magnification, and ■ is the fixed lens. The fourth group sp, which has a positive refractive power and functions to form an image, is a fixed aperture disposed 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 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 both of these two lens groups have positive refractive power. By setting the lens shape, lens thickness, etc. constituting the lens so as to satisfy the above-mentioned conditional expression, excellent aberration correction can be achieved over the entire zoom range.

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

Conditional expression (+) relates to the ratio of the radius of curvature of the image side lens surface of the 411th lens to the object side lens surface of the 412th lens, that is, the refractive power ratio. This is to better correct the spherical aberration generated on the side lens surface by the object side lens surface of the 4.2nd lens.If the upper limit value is exceeded, the spherical aberration will be overcorrected, and if the lower limit value is exceeded, the spherical aberration will be overcorrected. There will be a shortage.

Conditional expression (2) is mainly used to properly correct spherical aberration regarding the refractive power of the object-side lens surface of the 412th lens.If the upper limit is exceeded, the spherical aberration will be insufficiently corrected, and if the lower limit is exceeded, the spherical aberration will be insufficiently corrected. This results in over-correction.

Conditional expression (3) relates to the air distance between the 4.1 lens and the 4.2 lens, and is mainly used to correct spherical aberration and coma in a well-balanced manner.If the upper limit is exceeded, spherical aberration is corrected. If the lower limit is exceeded, a large amount of coma aberration will occur, which is not preferable.

Conditional expression (4) is the 42nd. This is related to the air distance between the lens and the 422nd lens, and is mainly used to correct coma aberration.If the upper limit is exceeded, inward coma aberration will occur, and if the lower limit is exceeded, outward coma aberration will occur. It's not good because it's coming.

Conditional expression (5) relates to the negative refractive power of the lens surface on the image side of the 421st lens, and is mainly used to properly correct distortion, make the entire lens system compact, and ensure sufficient back focus. If the upper limit is exceeded, barrel-shaped distortion will occur at the wide-angle end, and if the lower limit is exceeded, pincushion-shaped distortion will occur at the telephoto end, and it will be difficult to secure sufficient back focus. It's coming.

Conditional expression (6) relates to the ratio of the radius of curvature of the lens surface on the image side of the 4□1 lens and the lens surface on the object side of the 423rd lens, and is generated on the lens surface on the image side of the 421st lens. This is to better correct the pincushion-shaped distortion caused by the object-side lens surface of the 423rd lens; exceeding the upper limit will cause barrel-shaped distortion at the wide-angle end, and exceeding the lower limit will cause telephoto distortion. Pincushion distortion aberrations occur at the edges, and it becomes difficult to properly correct these aberrations.

In this example, in order to shorten the overall lens length and reduce aberration fluctuations during zooming, both lens surfaces of the third group are convex and have stronger refractive power on the image side than on the object side. It is best to use a single lens.

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.

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

Numerical Example I F-1 to 2.85 FNo=I:1.45 2ω-46
,5°~17.2°R1-6,7t2 D l proverb 0.
13 N l 1.80518ν 1-25.4R2-
2,880D 2-0.63 N 2-1.516:1
3ν 2-64. IR3--9,387D:l-0,
02R4-2,578D 4-0.41 N 3-1.
6:11354ν3=55.4R5-21,69305
-Variable R6-18,980D 6-0.11 N 4-1.6
9680ν 4-55.5R7-1,118D 7san0
．． 25 R8--1,46708-0,09N 5-1.49
831 ν 5-65, OR9-1, 46709■
0.19 N 6-1.84666 ν 6 servings 2
3.9RIO-5, 221010-Variable old l = Aperture Dll-Variable R12-7, 470012-0, 18N 7-1.65
844 Schiff~50.9R1:1--3.255 013
-Variable old 4 = 1.437 DI4 car 0.31
N8=1.65844 v8-50.9
R15--5,882DI5-0.03RI6--2.
948 DI6-0.11 N 9-1.75520
υ9-27.5RI7- 3.417 017-0.7
2R18= 7.464 018-0.11 Nl0
-1.80518 v 10-25.4RI9- 1.
629 019-0.09R20-3,466D20 Glue 0.30 N11-1.60311 Sill-60,7R
21--2,293D21-0.02R22-1,55
0D22 Seal 0.33 N12-1.69680 ν
12-55.5R23-22, +08 D23-0
．． 22R24= co D24=0.59 Ni
1-1.51633 v 13=64. lR25-ω b, f, ・1.16 (value calculated by converting a parallel plane plate into air)
Numerical Example 2 F-1 to 2.85 FNo-1: 1.45 2ω-
46.5° ~ 17.2° R1st 7.615 D 1-
0.13 N 1-1.805+8 v l-25,
4R2-3,18802-0,72N 2a1.516
33 v 2-64.1R3--8,099D 3-0
．． 02 R4-2, 54104-0, 4683-1, 63854
C3-55.4R5-14,562D 5-Variable R6--25.6+8 D 6=O, II N 4=
1.69680 v 4-55.5R7-1,2040
7-0,28 R8--1,52008-0,09N 5-1.498
31 v 5-65. OR9-1,520D 9-0゜1986-1.84666shi6-23.9RIO-4,
081010-Variable R11= Aperture Dll-Variable RI2- 7.405 012-0.19 N
7-1.65844 ν 7-50. 'IR1:]
--3.567 0I:l-Variable RI4- 1.52
9 014 Otori 0.32 N 8-1.65844
ν 8 torture 50.9R15--6,052015-0
,03R16--3.108 016 0.11
N 9-1.75520 ν 9-27.5R17
-5,376017-0,72 R18-13,951D18-0.11 N1011
1.80518 v 10-25.4R19-1,
582DI9-0.07 R20-2, 914020-0, 29N11-1.60
:111 Shi11-60.7R21 Tan -2,451
021-0,02R22-1,650022-0,30
N121.71300 v12-53.8R23-2
4,491023-0,22R24-ao
D24=0.59 N13-1.51633 ν1
3"64.1b, f, ・1.17 (Values when parallel plane plate is converted into air) The table shows the relationship between the various conditions of the present invention and the numerical examples of the present invention (effects of the invention). According to the invention, by setting the lens configuration of the fourth group, which is fixed during zooming of a zoom lens consisting of four lens groups with a fixed aperture disposed between the second group and the third group, as described above, the lens system can be improved. It is possible to achieve a zoom lens suitable for photographic cameras, video cameras, etc., which has high optical performance and is designed to be miniaturized as a whole.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of lenses of Numerical Example 1゜2 of the present invention, and FIGS. 3 and 4 are lens cross-sectional views of Numerical Example 1 of the present invention, respectively.
．． FIG. 2 is a diagram showing various aberrations of No. 2. In the aberration diagram (A), (
B) and (C) are aberrations at the wide-angle end, middle, and telephoto end, respectively. In the figure, I, II, III, and rV 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. Chapter 2

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. It has four lens groups: a third group with positive refractive power that moves with a convex locus toward the image plane in order to maintain the image, and a fourth group with positive refractive power that performs a fixed image forming function. A fixed diaphragm is provided between the second group and the third group, and the fourth group includes a 4-1 lens group with positive refractive power and a 4-2 lens group with positive refractive power. It has two lens groups, and the 4-1 lens group has a 4_1_1 lens with a positive refractive power that has stronger refractive power on the object side than on the image side, and a 4_1_2 lens with both lens surfaces concave. The 4-2nd lens group includes a 4_2_1 lens with a negative refractive power and a meniscus shape with a convex surface facing the object side, and a 4_2_1 lens with both lens surfaces convex.
2 lens and a 4_2_3 lens with a positive refractive power having stronger refractive power on the object side than on the image side, and the radius of curvature of the i-th lens surface counting from the object side of the fourth group is R_IV_i, the i-th lens thickness or air gap is D_IV_i, and the focal length of the entire system at the wide-angle end is f_
When w, 1.8<R_IV_2/R_IV_3<2.1 2.7<|R_IV_3/f_w|<3.3 0.03<D_IV_2/f_w<0.04 0.06<D_IV_6/f_w<0.09 A zoom lens that satisfies the following conditions: 1.5<|R_IV_6/f_w|<1.8 0.9<R_IV6/R_IV9<1.1.