JPH01120521A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a large aperture ratio and high variable power ratio and to reduce the size of the title lens by determining the focal length of the j-th lens of an i-th group, the air thickness or air spacing of the j-th lens of the i-th group, the focal length of the i-th group and the focal length of the entire system at a wide angle end so as to satisfy specific conditions. CONSTITUTION:This zoom lens has 5 lens groups of the 1st-5th groups successively from the object side. The 5th group has, successively from the object side, the six lenses; the lens having convex faces on both the lens faces the strong refracting face of which is directed to the object side, the meniscus-type lens the concave face of which is directed to the object side, the positive lens the strong refracting face of which is directed to the object side, the meniscus-type lens the convex face of which is directed to the object side, the lens having convex faces on both lens faces the strong refracting face of which is directed to the image plane side, and the positive lens the strong refracting face of which is directed to the object side. The conditions expressed by equations are satisfied when the focal length of the ij-th lens of the j-th group of the i-th group is designated as fi,j, the thickness or air spacing of the j-th lens of the i-th group as Di,j and the local length of the i-th group as Fi and the focal length of the entire system at the wide angle end as FW.

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, % inch tubes are often used as image pickup tubes for video cameras from the two viewpoints of 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 power ratio of about 6 is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-51813 and Japanese Patent Application 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 image plane fluctuations 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, but increasing the FNo will reduce the large aperture ratio. This is not very desirable for video cameras and the like that require a lens system. Generally, in order to reduce the size of the entire lens system while decreasing the FNo, it is important to appropriately set the optical constants of 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 predetermined optical performance.

In particular, when using a % inch image sensor, the effective screen diameter is φ
6, when the total lens length from the lens surface to the imaging surface is L, L = about 12.5φA to 14φ8, which means that the total lens length is relatively long, and the total lens length can be shortened while maintaining good optical performance. It becomes difficult to do.

(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 has 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 produce a divergent light beam from the third group, a fourth group with a positive refractive power to produce a substantially parallel light beam from the third group, and a fifth group with an imaging function. The fifth lens group includes, in order from the object side, a 51st lens having both convex lens surfaces with a strong refractive surface facing the object side, a 52nd lens having a negative meniscus shape with a concave surface facing the object side, and a 52nd lens having a negative meniscus shape facing the object side. A positive 53rd lens with a strong refractive surface facing the object side, a 54th negative meniscus lens with a convex surface facing the object side, a 55th lens with both convex lens surfaces facing the image plane side, and It has six lenses, including a positive 56th lens with a strong refractive surface facing the object side, and the focal length of the j-th 52nd lens of the i-th group is f l r J % of the i-th group. Let the j-th lens thickness or air spacing be D I * J , the first
When the focal length of the group is Fi and the focal length of the entire system at the wide-angle end is Fw, 1.45<F, /F4<1.65...(+
)2.5 < F4/F, <2.8 ・-
(2) 0, 75< l fs , 4 /Fs l <
1.3...(3)0.47<Ds,a/Fs
<0.65... (4) Please satisfy the condition.

(Example) FIG. 1 is a sectional view of a lens according to 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 make the divergent light beam from the third group into a substantially parallel light beam, ■ is the fifth group that has a fixed imaging function, and SP is a fixed aperture. It is.

In this example, in such a zoom type, the refractive power of each lens group and the lens configuration of the fifth group are determined by the above-mentioned conditional expression (1).
By satisfying the conditions (4) to (4), aberrations associated with a large aperture ratio and a high zoom ratio can be well corrected, and good optical performance can be obtained 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.

It should be noted that a refractive surface having a strong refractive power on the image side is 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.

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

Conditional expression (1) requires the first group for focusing and the fourth group for after focus.
Regarding the refractive power ratio of the groups, conditional expression (2) relates to the refractive power ratio of the fourth group and the entire system at the wide-angle end. Conditional expression (+
), the refractive powers of the first and fourth groups are set to satisfy (2), and as a result, the entire lens system has a well-balanced refractive power arrangement, the outer diameter of the lens is reduced, and the desired image formation is achieved. Aberration correction is easily performed while maintaining magnification.

When the refractive power of the fourth group becomes smaller by exceeding the lower limit of conditional expression (1), the amount of movement of the third group, which is a variable power unit, increases, and for this reason, the fourth group must be placed closer to the image plane. Instead, the outer diameter of the lens of the fourth group for receiving the diverging light beam from the third group increases. Also, when the upper limit is exceeded and the refractive power of the first group becomes weaker, the first group is moved closer to the object side in order to maintain an appropriate imaging magnification relationship with the variable magnification unit consisting of the second and third groups. This is not a good idea because the outer diameter of the first lens group increases.

If the lower limit of conditional expression (2) is exceeded and the refractive power of the fourth group becomes too strong, the imaging magnification of the variable power unit at the wide-angle end must be appropriately set, and the overall length of the lens may be shortened while the refractive power of the fourth group becomes too strong. 2
．． Third. It becomes difficult to set the fourth group in a well-balanced manner so that they do not interfere with each other, and many aberrations such as higher-order spherical aberration and coma aberration occur, making it difficult to properly correct them. Furthermore, if the upper limit is exceeded and the refractive power of the fourth group becomes too weak, it becomes difficult to make the divergent light beam from the third group afocal, and for this reason, the refractive power of the variable power section must be weakened. As a result, the amount of movement of the second and third groups during zooming increases and the overall length of the lens increases, which is not good.

Conditional expression (3) relates to the refractive power ratio between the fifth group having an imaging function and the 5-4th lens having negative refractive power. If the lower limit is exceeded and the refractive power of the 5-4th lens becomes too strong, the diverging power of the rear lens group of the 5th group becomes strong and a large amount of high-order astigmatism occurs. Furthermore, if the upper limit is exceeded and the refractive power of the fifth-fourth lens becomes too weak, negative distortion increases, and it becomes difficult to correct this well.

Conditional expression (4) concerns the air spacing between the 53rd lens and the 54th lens in the 5th group. 1. If the spacing becomes too short beyond the lower limit, the off-axis principal ray will be incident on the 54th lens and subsequent lenses. As the height becomes lower, it becomes difficult to properly correct the field curvature.Also, if the interval exceeds the upper limit and becomes too long, the lens diameter after the 54th lens will increase, and the total lens length will also become longer. So it's not good.

In this embodiment, it is preferable to configure the fourth group with a single lens with a convex surface facing toward the image plane in order to shorten the overall lens length and correct aberrations.

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

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

Numerical Example I Fllll~5.6 FNo-Il: 1.4~1.9
2(A)-47,6°~9.1'It 1-7.
758 D I-0,134N l-1,80
518v 1-25.482- 3.442 02-
0.591 N 2-1.51633 2-64. I
R3--9,53103-0,016 R4-2,763D 4- 0.388 N
3-1.60311 v 3-60.785- 1
1.218 D 5- Variable R6 = 14.30
7 0 6- 0.086 N 4-1.71
300v 4-53.8R7-1, 21507-
0,312 18 meetings -1,631D 8- 0.086
N 5 self 1.71300 ν 5-53.8n
9= 1.631 0 9- 0.257
N 6-1.84666 v 6=23.9R
IO--82,0690IG-variable R1+--2,373Dll-0,096N 7-1
．． 71300 ν 7maro53.8RI2maro-14,8
02D12- Variable R13 set 12.778 0
13- 0.419 N 8-1.69680
ν 8-55.5R14--2,092014-0,
107 Old 5 Proverbs Aperture D15-0.214 R16-3,733DI'6-0.333 N
9-1.65844 ν 9-50.9RI7-
-7.6 (CI D17-0.144R18=
-2,384018-0,107Nl0-1.80
518 SI1G=25.4RI9--13.781
019 torture 0.016820= 3.216
020- 0.236 Ni1-1.6:184
4 Shi1l-50.9821-26.338
021-1.719R22-9,547D22-0.
086 N12111.80518 C12-25.
4R23 Proverbs 1.909 023-0.065R
24-3,035024 0.333 N13 1.51+384 13-60.71125-
-:+-o35 025- 0. Old 61126-
'2.109 026- 0.300 N14-
1.51742 ν14”52.4R27--11,
863027-0,429R28-ω [128
-0,591N15 1.51633 15-64
．． 1R29-ω Numerical Example 2 F@1 ~5.6 FNo=l:1.4 ~1.
9 2ω-47,6'~9.1'Rl=8
．． 401 DI= 0.134 N
l-1,8Q518 v 1s25.4R2-3,
50202-0,612N2=1.51633v
2-64. IR3--7,35703-0,016 R4m2.552 04-0.397 N 3111
．． 60311 v 3-60.7R5-7, 03805
-Variable R6= 10.093 06-0.086 N 4
-1.71300 v 4=53.8R7-1,206
07-0,299 R8--1,50308-0,086N 5-1.7
1300 v 5-53.8R9= 1.5
03 D 9- 0.308 N 6-L
80518 v 6-25.4RIO--18,2
830IG-variable old 1 = -2,722011 = 0.096
N 7-1.71300 v 7-53.81
112--68.882 012- Variable R13=
22.343 DI3= 0.387, N
8-1.71300 v 8-53.81 (14th -2,035014-0,107RI5- Aperture [115-0,215R16-5,610016-
0,290N 9-1.65844 ν 9-50
．． 9R17--6,537017-0,176RI8-
-2.030 D18- 0.107 Nl0
-1.80518 SI1G-25.4019- -
5.427 019-0.016R20-3, +19
D20-0.268 Nil self 1.6385
4 Shi11-55.4R21--20,632D21
- 1.397R22 San 5.421 022 Zen 0.086 N12-1.80518 Shi12
-25.4123- 1.814 023-0.
115R24-4, 701024-0, 311N131
11.51633 y13-64.1R25--2,
435025-0,016R26=2.992
028=0.279 N14-1.5163
3 Shi14-64.1R27--7,814027-
0,430828=oo D28- 0
．． 591 N15=1.51633 y15=6
4. lR29-■ Numerical Example 3 F-1~5.6 FHo=1:1.4~1.92ω-
47,80~9.10R1-7,793D 1■ 0
．． 134N1 self 1.80518 ν 1-25.4
-R2=3.50302-0.569N2=1.516
33? /? 6-i, IR3--10, 46303-0,
016R4-2,80404-0,397N 3 sets 1
．． 60311 ν 3 pieces 60.7It 5- 12.
784 851- Variable R6 rin 10.092 0
6- 0.086 N 4-1.71300
ν 4-53.8R7-1, 247D 7-0.
2991 8- -1.632 0 8- 0.0
86 N 5-1.71300-J 5-53.
8R9 layer 1.720 09-IO, 268N 6-1
．． 80518 v 8~25.4R11)-204,8
43010-Variable Old 1--2.609 Dll
-0,096N 7-1.71300 ν 7 electric 5
3.8 old 2■-33,052012-variable R13-22,168D13=0.387 N g
-1,7130F) v 8-53.8R14--2,
037014■ 0', 107 old 5-fold aperture 015
-0.215 R1B-4,745016-0,2611N 9-1
．． 65844 v 9-50.9R17--8,7
24D17-0.190R18--2,0840180
0,107Nl011.805+8 υ10-25.
4R19 glue -5,021019-0,016R20-
3,134020=0.288 Ni1-1.
63854 Shi1l-55.4R21--48,80
9021-1,397R22=5.383 022
-0.086 N12-1.80518 ν12=2
5.4R23-1,798023-0,115R24-
4,523024-0,311N13-1.51633
C13-84. lR25--2,536D25-
0.016R26112,917D2[i=0.2
79 N14-1.5+633 v 14-64
．． lR27--6,661027-0,430R28-
co 028= 0.591 N15=
1.51633 v 15-64. lR29-■ Numerical Example 4 F-1 to 5.8 FNo-1: 1.4 to 1.9
2ω = 47.6' ~ 9.1'RI-7
,7546D 1-0.1343 N +-1,805
18ν 1-25.482- 3.441302-0.
5908 N 2-1.51633shi 2-64.1R3
--9,530103-0,0161R4-2,763
204-0,3867N 3-1.60311shi3-6
0.7R5-11, 216805-variable R6-14, 304906-0,0859N 4=1
．． 71300 v 4-53.8R7-1,215
707-0,3111R8=-1,6307D 8
s0.0859 N 5 = 1.71300 v 5-5
3.8R9-1, 631509-0, 2578N 6-
1.84666 6-23.98IO 82,054
0010-variable 111 hours -2,3730 [111 hours 0
．． 0967 N 7-1.71:100 shear 53.8
R12-14,7996DI2- Variable RI3-1
2.7764013-0.4190 N 8-1.69
680ν8-55.5R14--2,0921014-
0,1074R15 Aperture 015-0.2149
RI6- 3.7329016-0.333089-1
．． 65844shi9-50.9R17--7,60250
17-0, 1448R1B--2, 3838018-0
, 1074N10-1.80513ν10-25.48
19- -13.7788 019- 0.0161R
20■ 3.2163 020- 0.2363
N11-1.65844 ν ll-50,9R2
1 position 26.3335 021- 1.7188R2
2-9,5453D22- 0.0859 N12-
1.80518 C1.2-25.4R23-1,9
093023-0,0654R24-+ 3.03
51 024- 0.3330 813-1.5638
4 v I3 proverb 60.7R25--3,035002
5 self 0.0161R26= 2.1092 02
6 @ 0.3008 N14-1.51742 v
14=52.4R27--11,8616027
0.4297R28-ω D28 set 0.590
8 N15-1.51633 C15764. lR
29 depletion ω (Table 1) (Effect of the invention) As shown below, according to the present invention, a photograph with a large aperture ratio, a high variable power ratio, and a high optical performance with a compact lens system as a whole can be obtained. A zoom lens suitable for commercial cameras and video cameras can be achieved.

In particular, in the present invention, the total length of the lens is L = 11.2φ, ~1
A compact zoom lens as short as 1.6φ8 can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a lens according to Numerical Example 1 of the present invention, and FIGS. 2 to 5 are aberration diagrams of Numerical Examples 1 to 4 of the present invention, respectively. In the aberration diagrams, (A) is an aberration diagram at the wide-angle end, and (B) is an aberration diagram at the telephoto end. 1 in the figure. II, III, ■, and V are respectively 1st. 2nd゜3rd. 4th. 5th group, ΔM is meridional image plane,
ΔS is the sagittal image plane, d is the d-line, g is the g-line, and sp is the aperture. Fig. 1111V'V' Fig. 2
Figure (B) 1 3 Figure (A) F, b, 4 tJ=21B@u=23.8'
6J=23.8° 3 Figure (B) Figure 4 (A) Figure 4 ('B) F/1.9 u=4,55° t, y =
4.55' t, y = 4,559 high 5
Figure (A) f-71,4tJ=218” u=23.8
'Flash: 23.86 [F/1.9 ω=4.55'''D
6 mouths (B) Member = 4.55° ω = 4.55°, LI
Ll'), IJU-Q005 Tamaki M (difference, (%) Double type Shimata Thorn.

Claims (1)

[Claims] (1) In order 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 corrects the image plane that changes due to variable magnification. a third group with negative refractive power; a fourth group with positive refractive power for making the diverging light beam from the third group into a substantially parallel light beam;
The fifth lens group includes a fifth lens group having an image forming function, and the fifth lens group includes a 51st lens in which both lens surfaces are convex with strong refractive surfaces facing the object side, and a concave lens facing the object side. A 52nd lens with a negative meniscus shape with a strong refractive surface facing the object side, a 54th lens with a negative meniscus shape with a convex surface facing the object side, a 54th lens with a negative meniscus shape with a strong refractive surface facing the object side, and a strong refractive surface facing the image side. It has six lenses: a 55th lens with both convex lens surfaces facing toward the object side, and a positive 56th lens with a strong refractive surface facing the object side, and the jth lens of the i-th group The focal length of the i-th group is f_i_, _j, the j-th lens thickness or air gap of the i-th group is D_i_, _j, the focal length of the i-th group is F_i, and the focal length of the entire system at the wide-angle end is F_w.
When 1.45<F_1/F_4<1.65 2.5<F_4/F_w<2.8 0.75<|F_5,_4/F_5|<1.30.47
A zoom lens characterized by satisfying the following condition: <D_5,_6/F_5<0.65.