JPS6380215A - Zoom lens - Google Patents

Abstract

PURPOSE:To make the whole lens system small in size and light in weight by constituting the titled lens so that a radius of curvature of a lens surface, thickness of a lens or an air interval, and a focal distance of the whole system in a wide angle end satisfy specific conditions. CONSTITUTION:The titled zoom lens is provided with the first group having a positive refractive power for focusing, the second group having a negative refractive power for moving monotonously to an image surface side in case of a variable power, the third group having a positive refractive power, which is fixed in the course of the variable power, the fourth group having a positive refractive power for moving on an optical axis while having a projecting locus on an object side in order to maintain an image surface varied by the variable power, in a prescribed position, and a fixed diaphragm which has been placed between the second group and the third group. In such a state, when a radius of curvature of the surface of the i-th lens counted from the object side of the fourth group, thickness of the i-th lens or an air interval, and a focal distance of the whole system in a wide angle end are denoted as RIVi, DIVi, and fw, respectively, conditions of the expressions are satisfied. In such a way, by placing the diaphragm in about a middle position of the optical system, the front- element diameter of the first group is reduced, and the whole lens system can be miniaturized.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a compact zoom lens, and particularly to a compact zoom lens that moves the lens group closest to the image plane during zooming to correct image plane fluctuations caused by zooming. The present invention relates to a zoom lens having high optical performance suitable for photographic cameras, video cameras, etc., in which the entire lens system is miniaturized by arranging an aperture at an appropriate position in the lens system.

(Prior Art) A zoom lens having a configuration shown in FIG. 1 is a typical zoom lens conventionally used in photographic cameras, video cameras, and the like. In the figure, 11 is the first group with positive refractive power for focusing, 12 is the second group with negative refractive power that mainly functions to change the magnification and moves monotonically, and 13 is the correction for image plane fluctuations associated with changing the magnification. A third lens with negative refractive power that moves convexly toward the object in order to
14 is a fixed positive refractive power fourth group arranged as necessary to make the light beam passing through the first group to the third group almost parallel; This is the fifth group with positive refractive power. Reference numeral 16 denotes a diaphragm, which is often arranged between the third and fourth groups or between the fourth and fifth groups.

The zoom lens shown in Figure 1 moves the second and third groups when changing magnification, and also moves the aperture to the fifth group, which is far away from the first group.
It is placed near the group. For this reason, when attempting to secure a certain amount of off-axis light during focusing and zooming, the lens diameter of the first group tends to increase, making the entire lens system larger.

In such a lens system, when trying to move the first group during focusing, a large driving force is required. For example, when applied to an automatic focusing device, a motor with a large driving force is required, and power consumption is also high. There were also problems such as the increase in

This is not very desirable as a photographing lens for a video camera, which is required to have a more compact photographing system due to the recent integration of video cameras and video recorders.

As a shooting lens for a video camera, it is a zoom lens that is not only small and lightweight but also has high optical performance.
Furthermore, a protective glass is placed on the front of the image pickup device such as the image pickup tube or CCD.
It is required that there be a space of sufficient length for arranging various filters such as a stripe filter for color separation and a low-pass filter, that is, that there be 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 aims to reduce the overall length of the lens and the diameter of the first lens group, thereby making the entire lens system smaller and lighter. The purpose of the present invention is to provide a compact zoom lens suitable for cameras, etc., and having high optical performance.

(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 second group has a positive refractive power that is fixed during changing magnification. There are four lens groups: a third group with refractive power, and a fourth group with positive refractive power, which moves with a convex trajectory toward the object in order to maintain a constant position on the image plane that changes as the magnification changes. and a fixed aperture is provided between the second group and the third group, and the fourth group includes a 4-2 lens group with positive refractive power as well as a 4-1 lens group with positive refractive power. The lens group 4-1 has two lens groups.
The lens group consists of a 4th lens with positive refractive power that has stronger refractive power on the object side than on the image side, and a 41st lens with both lens surfaces concave.
2 lenses, the 4-2nd lens group is a meniscus-shaped 421st lens with negative refractive power with 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 R7qL is the radius of curvature of the th lens surface, DrgL is the thickness or air gap of the ith lens, and fw is the focal length of the entire system at the wide-angle end, then a < RIv2/RIv3 < 2.1.
-- (1): 1.0 < l RW3/fw +
< 3.4 -------- (2) 0.02 < D
r72/fW < 0.04−−−−−− (+)0
．． 06 < DWG/fw < 0.09----
-- (4) 1.6 < l Rye/ f w I
< 1.9 ..." (5) 1.0 <
RIvG/Rwq < 1.3 -----
-- (6) must be satisfied.

(Example) FIG. 2 is a sectional view of a lens according to Numerical Example 1 of the present invention.

In the figure, the first group has positive refractive power for focusing, ■ is the second group with negative refractive power that moves monotonically toward the image plane when changing magnification, and ■ has positive refractive power that remains fixed during changing magnification. The third lens group ■ is the fourth lens group with positive refractive power that moves on the optical axis while having a convex locus toward the object side in order to maintain a constant position on the image plane that changes as the magnification changes. This is a fixed 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 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.

Then, the second and fourth groups are moved as described above to change the magnification, making effective use of the space between the third and fourth groups, shortening the overall length of the lens, and achieving a predetermined variable magnification ratio. Efficient < f$
ing.

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

Conditional expression (1) is based on the lens surface on the image plane side of the fourth □ lens and the fourth
This relates to the ratio of the gravity radii of the object-side lens surface of the 12th lens, that is, the refractive power ratio, and the spherical aberration generated on the image-side lens surface of the 41st + lens is expressed as the spherical aberration of the object-side lens of the 41st lens. This is to better correct the surface. If the upper limit is exceeded, the spherical aberration will be overcorrected, and if the lower limit is exceeded, the spherical aberration will be undercorrected.

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; exceeding the upper limit value will result in insufficient correction of spherical aberration, and exceeding the lower limit value will result in insufficient correction of spherical aberration. This results in over-correction.

Conditional expression (3) relates to the air gap between the 411th lens and the 4.2nd lens, and is mainly used to correct spherical aberration and comatic aberration in a well-balanced manner.If the upper limit is exceeded, spherical aberration will be insufficiently 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 relates to the air gap between the lens and the 422nd lens, and is mainly used to correct coma aberration.If the upper limit is exceeded, inward coma aberration occurs, and if the lower limit is exceeded, outward coma aberration occurs. It's not good because it comes.

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 421st lens and the lens surface on the object side of the 423rd lens. This is to better correct the type distortion aberration by the object-side lens surface of the 423rd lens. If the upper limit is exceeded, barrel-shaped distortion will occur at the wide-angle end, and if the lower limit is exceeded, pincushion will occur at the telephoto end. Type distortion aberrations occur, and it becomes difficult to satisfactorily correct these aberrations.

In this embodiment, in order to reduce the aberration fluctuation during zooming while shortening the overall lens length, the third group is configured such that both lens surfaces have approximately the same radius of curvature, for example, within ±10%. It is best to use a single lens with a convex surface.

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. R25 and R26 are optical members such as a face plate and a filter.

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

Numerical example! F-1~2.85 FNo=l:1.45 2ω-4
6.5°~17.2°) t 1- 6.251 D
I-0,13N I-1,80518ν 1-25.4
R2 Liao 3.070 D 2-0.67 N
2-1.51633 ν 2-64. IR3--
7,81303-0,02 R4-2,606D 4th 0.35 N 3-1.63
854shi3-55.4R5-11,07505-variable R6-78,18706-0,11N 4-1.696
80ν 4-55.5R7-1, 20407-0, 29 n 8=-1,458D B-IO, 09N 5-1.
49831 v 5J5. OR9 1.458 D
9■0.19 N 6111.84666 v 6-
23.9RIO-3,870010-Variable R11-Aperture Dll-0,25 R12= 4.588 012-0.19 8
7-1.66672 -1) 7=48.3R13--
4,588013-Variable 1114- 1.617 D14-0.31 N 8
-1.65844 shi8 50.9R15 dew -6,22
9015-0, 03R16--3, 200016-0,
11N 9-1.75520shi 9-27.51117 layers 3.200 017-0.88n18-11.6
62 D18-0.11 N10-1.80518ν
10-25.4R19-1,753019-0,07 R20= 3.162 020-0.31 N
i1-1.60311 v 1l=60.7R21-
-2,508021-0,02R22=1.558
022-0.39 N12-1.71300 υ
12-53.8R23-22.475 D23-0
．． 22R24-oo D24-0.59 N
15J, 51633 C13-64. lR25 kick
ω b, fw-1,25 (value calculated by converting the parallel plane plate into air) Numerical Example 2 FIIl~2.85 FNo=1:1.45 2(L
l-46,5'~17.2°RI=6.150
D1=0.13 N1-1.80518
v 1-25.4n 2- : 1.078
D 2-0.67 N 2-1.5163
3 v 2-64. IR3--7,90903-0
, 02 R4-2, 61104 0.35 N 3 ■ 1.6
3854 ν 3 words 55.4R5-10,892D
5-Variable R6-51, 61806-0, 11N 4-1.69
350 ν 4-53.2R7-1, 194D 7
-0.29 R8--1,45608-0,09N 5-1.49
831 v 5=65. OR9-1,456D
9-0゜19 N 6 Liao 1.134 [i88 ν 6
-23.98IO-3,979010-Variable R11-Aperture Dll-0,25 R12-4,572012-0,1987-1,666
72v 7-48.3R13--4,572013-variable old 4- 1.615 014=0.31 N
8-1.65844 v 8-50.9R15--
6,197015-0,03 old 6--3.194 D
I6=0.11 N 9-1.75520 v 9-2
7.5R] 7- 3.194 017-0.88R18
= 11.948 D18-0.11 Nl0-1.
80518 v 1O=25.4RI9- 1.751
019-0.07R20-3, 142020s0.3
1 Ni1-1.60311 v 11-60.7
821--2.509 021-0.02R22-1
,553022-0,38N+2-1.71300v
12-53.8R23-22,722023-0,22
r124=oo D24-0.59 N13-
1.51633 v 13-64.1R25maro ω b, fw-1,25 (value obtained by converting the parallel plane plate into air) Numerical Example 3 F-1 ~ 2.85 FNo=l: 1.45
2ω -46,5' to 17.2'Rl=6.
198 DI=0.13 N 1-1.805+8
v 1-25.4R2-3,07002-0,67
N 2-1.51633 Z/ 2-64.193--
7.761 03-0.02 n 4= 2.605 0 4-0.35
N 3-1.63854 v 3-55.4R5
-10,76105~Variable R6=-73,83806=0.11 8 4-1.6
9680 v 4-55.5R7maro 1.204
D7-0.29R8=-1,45708-
0.09N 5-1.49831 v 5=65. OR
9-1,45709-0,1986-1,84666 6-23.9RIO-3,882010-Variable R11-Aperture Dll-0,25 1112 4.570 012 0.19 N
7-1.65844 ν 7厘50.9R13-
-4,570013-Variable R14~ 1.614 D14-0.31 N
8-1.65844 ν 8-50.9R15-
-6,200015 0.03R16s -3,197
D16-0.11 N 9-1.75520 v
9-27.5R17-3, 197017-0, 88 R18-10, 912018-0, 11N10-1.8
0518ν10-25.4R19-1, 750019-
0,07 R20-3,196D20-0.31 N11-11
．． 60311 vll-60,7R21--2,52
9D21-0.02R22■ 1.553 022-0
．． 39 N12-1.71300 Shi12 Proverbs 53.
8R23-23.091 023-0.221124
Self (1) D24 night 0.59 N13 Seal 1.51633 Shi13 torture 64.1R25-o.

b, fw-1, 25 (value obtained by converting the parallel plane plate into air) Numerical Example 4 F-1 to 2.85 FNo-1: 1.45 2ω-4
6,5' to 17.2'Rl-6,231D I-0,
13N 1=1.80518 v l-25,482
-3゜12202 self0.66 N 2-1.516
33 ν 2-64. IR3--7, 73703-0
,02 R4 San 2.603 D 4-0.37 N
3-1.63854 ν 3 Maro55.4R5-1
0,49405-Variable R6--124.354 D 6-0.11 N 4
Electricity 1.69680ν4-55.587- 1.204
D 7-0.29R8--1,466D 8-0.
09 N 5-1.49831 ν 5-65.
OR9 Hatake 1.466 D 9-0.19
N 6-1.84666 υ 6-23.9 old 0-
3.813 0IG-Variable R11- Aperture Dll-0,25 R12 Cod 4.762 D12-0.19 N
7-1.65844 ν 7-50.9R13-
-4,762D13-Variable R14-1,642D14-0.31 N 8=1
．． 65844 v 8-50.9R15--6,3
89D15-0.03R16--3, 206016-0
,11N 9-fw75s2o ν 9son27.5
R17-3, 206 D17 0.94 R18-11, 26918 So 0.11 Nl0-1.
80518 Shi10-25.4R19-1,829D
19-0.08 R20-3, 543020-0,:II Ni1-1
．． 62299 Shi11-58.2R21--2.56
7 021-0.02R22-1,559022-0
,39N12 1.71300 Shi12 filter 53.8R
23 wings-24.059 D23 seal 0.22R24-
oo D24-0.59 N13-1.5
1833 Shi13-64.1R25maro ω b, fw・1.31 (value when parallel plane plate is converted to air'
) Table 1 (Effects of the Invention) According to the present invention, among the four lens groups, the second
By moving the lens group and the fourth group as described above, specifying the lens shape of the fourth group as described above, and adopting a lens configuration in which the aperture is placed between the second group and the third group, By shortening the overall lens length and reducing the lens diameter of the first group,
It is possible to achieve a zoom lens with high optical performance that is designed to reduce the size of the entire lens system.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the optical system of a conventional zoom lens, and FIG. 2 is a cross-sectional view of the lens of Numerical Example 1 of the present invention. 4th.
Fifth. FIG. 6 is a diagram showing various aberrations of numerical examples 1 to 4 of the present invention. In the aberration diagram, (A), (B), (
C) shows aberrations at the wide-angle end, middle, and telephoto end, respectively. Arrows in the figure indicate the moving direction of the lens group during zooming. ΔS is the sagittal image plane, ΔM is the meridional image plane, I, n, I[
[, IV are the first, second . Third. This is the fourth group. Patent Applicant Canon Co., Ltd. Agent Yukio Takanashi

Claims (1)

[Claims] In order from the object side: a first group with positive refractive power for focusing, a second group with negative refractive power that moves monotonically during zooming, and a second group with positive refractive power that is fixed during zooming. It has four lens groups: a third group and a fourth group with a positive refractive power that moves with a convex locus toward the object side in order to maintain the image plane that changes as the magnification changes at a constant position. A fixed aperture is provided between the second group and the third group, and the fourth group includes two lenses: a 4-1 lens group with positive refractive power and a 4-2 lens group with positive refractive power. group, and said No. 4-1
The lens group includes 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, and the 4-2 lens group is directed toward the object side. Meniscus-shaped fourth __ of negative refractive power with convex side facing
It has a 2_1 lens, a 4_2_2 lens with both convex lens surfaces, and a 4_2_3 lens with a positive refractive power that has stronger refractive power on the object side than on the image side, counting from the object side of the fourth group. The radius of curvature of the i-th lens surface is R
_IV_i, the i-th lens thickness or air spacing is D_
IV_i, where f_w is the focal length of the entire system at the wide-angle end, 1.8<R_IV_2/R_IV_3<2.1 3.0<|R_IV_3/f_w|<3.4 0.02<D_IV_2/f_w<0.04 A zoom lens that satisfies the following conditions: 0.06<D_IV_6/f_w<0.09 1.6<|R_IV_6/f_w|<1.9 1.0<R_IV_6/R_IV_9<1.3.