JPH0392808A - Zoom lens - Google Patents

Abstract

PURPOSE:To reduce the size of a whole lens system with about X3 - X4 high zoom ratio and to obtain excellent optical performance over the entire zooming range by specifying the refracting power and lens constitution of a lens group. CONSTITUTION:The zoom lens has a 1st group with negative refracting power, a 2nd group with positive refracting power, a 3rd group with negative refracting power, and a 4th group with positive refracting power in order from the object side. Then zooming is executed from the wide-angle end to the telephoto end by moving the 2nd and 3rd groups to the object side and the respective elements are so set that the paraxial lateral power variation rate of the 3rd group is always positive. Here, -1<M4/M3<0.8, where M3 and M4 are the amount of travel of the 3rd and 4th groups when zooming from the wide-angle end to the telephoto end. Consequently, the overall lens length is shortened with about X3 - X4 zoom ratio and the high optical performance is obtained over the entire zooming range.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a compact zoom lens suitable for lens shutter cameras, video cameras, etc., and in particular shortens the hack focus and shortens the overall length of the lens (from the first lens to the image This invention relates to a compact zoom lens that has four lens groups as a whole and is designed to shorten the distance (to the surface).

(Prior Art) Recently, with the miniaturization of cameras such as lens shutter cameras and video cameras, there has been a demand for compact zoom lenses with short overall lens lengths. Among these, the present applicant has developed a relatively small zoom lens that includes a standard angle of view (photographing angle of view 2ω = 47 degrees and a focal length of about fl 50 mm when converted to a 35 mm still camera).
This method has been proposed in Publication No. 4 and Japanese Unexamined Patent Publication No. 64-72114.

These publications have three lens groups in order from the object side: the first group with negative refractive power, the second group with positive refractive power, and the third group with negative refractive power. All of them disclose so-called three-group zoom lenses with a variable power ratio of about 2 to 3, which are moved toward the object side under certain conditions to change the power from the wide-angle end to the telephoto end.

Generally, in a zoom lens, if the refractive power of each lens group is strengthened, the amount of movement of each lens group to obtain a predetermined variable power ratio will be reduced, and the total length of the lens can be shortened. However, simply increasing the refractive power of each lens group will increase aberration fluctuations with zooming, so when aiming for a high zoom ratio of 3 or more, it is difficult to obtain good optical performance over the entire zoom range. The problem is that it becomes difficult.

(Problems to be Solved by the Invention) The present invention further develops the zoom lens proposed in Japanese Patent Application Laid-open No. 63-271214 and Japanese Patent Application Laid-Open No. 64-72114, which the applicant has previously proposed, and has four lenses as a whole. It consists of lens groups, and by appropriately setting the movement conditions of each lens group and the lens configuration of each lens group, it has a zoom ratio of about 3 to 4 while particularly shortening the overall lens length, and covers the entire zoom range. The purpose is to provide a zoom lens with high optical performance.

(Means for Solving the Problems) The zoom lens of the present invention includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a negative refractive power, and a positive refractive power. It has four lens groups, a fourth group having a refractive power of The lens is characterized in that each element is set so that the paraxial lateral magnification of the fourth group is always positive when changing the magnification.

In particular, in the present invention, the amount of movement of the third and fourth groups is set to M3 when changing the magnification from the wide-angle end to the telephoto end while having the above-described configuration.
, M4, and when the amount of movement toward the image plane side is positive, -1< M4/M3 <0.8 (1)
It is characterized by satisfying the following conditions.

(Example) FIG. 1 is a schematic diagram showing the paraxial refractive power arrangement of the zoom lens of the present invention. In the figure, (W) shows the zoom position at the wide-angle end, and (T) shows the zoom position at the telephoto end.

Moreover, FIGS. 2 to 4 show numerical examples 1 to 3 of the present invention, respectively.
FIG. 3 is a sectional view of the lens.

In the figure, ■ is the first group with negative refractive power, and ■ is the second group with positive refractive power.
The group ■ is the third group having negative refractive power, and ■ is the fourth group having positive refractive power. The arrows indicate the movement direction of each lens group when changing the magnification from the wide-angle side to the telephoto side.

In the zoom lens according to this embodiment, when changing the magnification from the wide-angle end to the telephoto end, at least the second group and the third group are both independently moved in the object side direction, as shown in each figure.

Each element is set so that the paraxial lateral magnification of the fourth group is always positive during zooming from the wide-angle end to the telephoto end. This makes it easy to achieve a zoom lens that has a high zoom ratio of 3 to 4 and has high optical performance over the entire zoom range.

Furthermore, in the present invention, in order to easily obtain a predetermined variable power ratio while further downsizing the entire lens system, when a zoom lens is constructed from the four lens groups having the above-mentioned refractive power, the fourth group is When moving the zoom lens, the amount of movement of the third and fourth groups for zooming from the wide-angle end to the telephoto end is set so as to satisfy conditional expression (1).

This makes it easy to obtain the desired zoom ratio, maintain good optical performance over the entire zoom range, shorten the back focus at the wide-angle end, and significantly shorten the overall lens length at the wide-angle end. There is.

Next, the technical meaning of conditional expression (1) will be explained.

In the so-called four-group zoom lens of the present invention, which is made up of four lens groups, the composite refractive power of the front lens group made up of three lens groups, the first, second, and third groups, is φI23, and the refractive power of the fourth group is φ4. Then, the refractive power Φ of the whole system is Φ=φ123+φ4 −eφI23 'φ4−・− ・
・(2) becomes.

Here, e is the principal point interval from the rear principal point of the front lens group to the front principal point of the fourth group.

In the zoom lens in this example, the composite refractive power φ1
23 becomes a positive value and becomes smaller when changing the magnification from the wide-angle end to the telephoto end. Further, the refractive power φ4 is fixed at a positive value. Therefore, in order to make the composite refractive power Φ even smaller when changing the magnification, that is, to obtain a higher zoom ratio, the value of the principal point spacing e should be increased when changing the magnification from the wide-angle end to the telephoto end. Become.

Therefore, in this embodiment, when changing the magnification from the wide-angle end to the telephoto end,
When moving the fourth group with respect to the third group so as to obtain the most effective zoom ratio, the movement at this time is expressed by the conditional expression (1
), and the change in the value of the principal point spacing e in equation (2) is increased. This effectively achieves both miniaturization and a high zoom ratio of the entire lens system.

That is, by configuring each element so as to satisfy conditional expression (1), compared to the three-group zoom lens shown in the above-mentioned Japanese Patent Laid-Open No. 63-271214 and Japanese Patent Laid-Open No. 64-72114, This makes it easy to obtain a larger zoom ratio.

In particular, in this embodiment, even if the fourth group is fixed during zooming (
M4=O), as long as the relative motion satisfies the equation ( ]), a high zoom ratio can be achieved, and in this case, the mechanism can be simplified.

When the upper limit of conditional expression (1) is exceeded, the 3rd and 4th groups are
The distance between the groups becomes smaller, the entire lens system becomes larger, and when the lower limit is exceeded, the 4th group becomes the imaging plane (film plane) at the telephoto side.
It's not good because it comes too close to.

In addition, in the present invention, in order to obtain high optical performance over the entire zoom range while shortening the overall lens length and ensuring a predetermined zoom ratio, the focal lengths of the second and third groups are each set to f.
2, f3, then 0.8<l f3/f2 l<1.
4 It is better to satisfy the following condition (3).

When the upper limit of conditional expression (3) is exceeded, the third
This is not appropriate because the refractive power of the group becomes too weak and the amount of movement of the third group must be increased in order to obtain a predetermined variable power ratio, which increases the size of the entire lens system. Alternatively, the refractive power of the second group becomes too strong, the Betzval sum becomes large in the positive direction, and the image plane characteristics, especially at the middle part of the zoom, are greatly under-slanted, which is not appropriate. Moreover, if the lower limit of conditional expression (3) is exceeded, the refractive power of the second group in particular becomes too weak, and the movable parts necessary for zooming, that is, the distance between the first group and the third group, must be ensured large. This is not appropriate because the lens system as a whole becomes larger as a result of this necessity.

In addition, in the present invention, in order to satisfactorily correct distortion aberration and image curvature, especially in the peripheral area of the screen, the focal length of the fourth group is f4.
It is preferable to satisfy the following condition: 1.5<f4/fw<7.0 (4), where fw is the focal length of the entire system at the wide-angle end.

When the refractive power of the fourth lens group becomes weak beyond the upper limit of conditional expression (4), it is necessary to increase the amount of movement of each lens group in order to obtain a predetermined variable power ratio according to expression (2). This is not a good idea because the entire lens system becomes larger. If the refractive power of the fourth group exceeds the lower limit and becomes too strong, barrel-shaped (negative) distortion will increase at the wide-angle end, and the Betzval sum will increase in the positive direction, causing image distortion, especially at intermediate zoom positions. This is not good because the surface curvature will be insufficiently corrected.

In addition, in the present invention, the above-mentioned conditional expression (+.) is set to -0.2.
<M4/M3 <0.3 It is preferable to set as in (5) because it is possible to further downsize the entire lens system and increase the zoom ratio while maintaining high optical performance.

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 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 Abpe number of the glass of the i-th lens, respectively, in order from the object side.

When changing the magnification from the wide-angle end to the telephoto end, the fourth group moves toward the object side in Numerical Example 1, is fixed in Numerical Example 2, and moves toward the image side in Numerical Example 3. There is.

Moving the fourth group toward the image plane side is the type that contributes most to variable power, and is preferable for achieving high variable power.

Furthermore, in Numerical Examples 1 to 3, when changing the magnification from the wide-angle end to the telephoto end, the total lens length at the wide-angle end is effectively shortened by moving the first group toward the object side. ing. In other words, the lens has a refractive power arrangement in which the overall length of the lens is short on the wide-angle side and long on the telephoto side.

Shamani Example 1 F~36~136 R I- -86.73 1+ 2- 27.35 11 3- 30.71 R 4- 435.93 115-3735 R 6- -82.08 0 7~ 25. 27 0 8・-26. fi9 R 9- 145.9 Old 0/Aperture Rl1/4'l. 89 RI2- 22.45 R13・ 1115.92 1114- −66.58 RI5 Tan 1:l3.06 RI5- −35.97 RI7- 116.48 RI8- 35.81 RI9- −13.6 820・−3844 .91 FNo-1: 3.5 ~B, ID ]- 1.75 D 2- 2.45 0 3 # 4.06 D4・Variable D 5- 3.58 D 6- 0.20 D 7- 5 .47 D B@1.6] D 9- 3.67 DIO- 2.72 0-1.33 DI2= 0.56 D+3- 2.26 DI4- Variable 015- 2.27 Dlli・0.20 017 @1.10 018- 6.38 019・1.50 020・Variable 2ωlI61 9°～18.1' 83481 1～42 N 2・l 14077 2-27 5+633 3-64.1 N 4・1.58267 5 -1.84666 4-46.4 5-2:1.9 N 6-1 113400 6-37.2 7・1.58893 7-31.1 8-158144 8・40,8 83400 9-37 NIQ- 1 60311 ν10-60 R21-163J+ D21- 4.83 N11~1.60311 νI +-50.7 R22- 106.34 M4/M3 ・0. +6 f3 / f21・ 0.94 f4 / “Kou # 2 97 Numerical Example 2 F-36.2 FNo・I: 2.8 ~ 110.0
~7. I R l- -76.01 D I・1.70R2・
27.71 0 2- 3.09R 3- 33.
47 0 3-4.0IR 4-398.8
2 D I/Variable R 5- 48.22
D 5・286R 6- -80.36 [)
6- 0.20R 7- 31. ! +9 0 7-
5.562ω-61.7°～22.2' 1-1.77250 1-49 2・1.72825 2・28.5 3～1.51633 3-64.1 N 4婁1 57135 4・53, O R 8- -24.90 R 9- 439.82 1110・Rl+- 59.98 Rl2- 27.72 1113・52.79 RI4 ball-42.04 RI5~133.61 Rl6- -38.23 RI7- -23.5O R+8-2030.23 1119・-57.28 R20- 70.6S R2+- 74.63 n22- 212.84 D 8- 2.62 0 9- 3.00 DIO wealth 3.18 DI+・ 3.03 012・ 0.68 DI3- 2.91 014・ Variable 015- 3.50 DI6- 5.74 017- 1.20 DI8- 1.12 019・ 1 50 020- Variable D2+・ 2.79 5 -1.84666 83400 69895 N 8-158144 9-1.83400 NIO・l 62299 N11-1.60311 5-23.9 6-37.2 7-30.1 8-4 (1.8 9-37. 2 ν10-511.1 νII-60.7 M4 / M:1 f3 / f21- 1.08 f4 7 fw ・5.22 0 Numerical example 3 F-16.2 ~ 145 R l- -87.43 R 2- 27.78 It 3= 31.6: ] R4・563.42 R 5- 40.87 R 6- -70.52 R 7- 28.08 R 8- -28.91 R9 161.82 1 {l〇1 Aperture nl+- 411.12 1112- 22.6O R+3 key 44.1O R+4 book -65 35 Rl5- 512.26 0 FNo-1+3.5 ~9.0 DI- 1.75 D 2・2 .71 D 3・4,14 D4- Variable D 5- 3.56 0 6- 0.20 0 7- 5.86 D 8- i.63 D 9・ 5.18 D+O- 2.61 DI1- 1. :13 DI2~ 0.81 DI3- 2.48 DI4 - Variable 015- 2.28 2ω-61.7°~+7' 1~1.83481 1-42.7 2-1.74077 2-27.8 3 -1.51633 : ] -1.1 N 4・1.58267 ν 4・46.4N 5
-1.84666 ν 5・23,96-1.834
00 6.37.2? ■1.68893 7-31.1 N 8-1.58144 8・40.8 R+6- -35.1/1 n+7- 53.4O Rll1- 29.51 Rl9- -14.70 R 2 0~-4 (19.71 1121-499.37 R22~ -72.47 D16-D17-D18-Dl9- 020・D21- 0.10 1,30 5,55 1.50 Variable 3.75 83400 N10・1.60311 Nll San1 60311 9-37.2 ν10 loincloth 60.7 νII・60,7 M4/M3・−0.07 f3/f21～] .0206 f4/fw −3.87 In addition, in the present invention, especially on the wide-angle side In order to effectively compensate for inward coma flare and barrel-shaped negative distortion caused by downward rays, at least one lens surface in the first group should have a positive refractive power that increases toward the lens periphery. Alternatively, it is better to use a non-spherical lens whose negative refractive power is weakened.

In addition, barrel-shaped f't distortion at wide-angle flu and telephoto f't
In order to satisfactorily correct the inward coma aberration caused by the upward rays at il+, the positive refractive power of at least one lens surface in the third or fourth group becomes weaker toward the lens periphery; Alternatively, it is better to use an aspherical lens with a shape that increases negative refractive power.

In the present invention, when changing the magnification, the lens group in the second group may be divided into two lens groups and moved separately, which reduces aberration fluctuations and further increases the magnification. It becomes easier.

In the present invention, focusing is performed by moving the first group because it reduces aberration fluctuations, but it is also possible to perform focusing by moving the third or fourth group. It is also possible to focus only on the object distance range.

(Effects of the Invention) According to the present invention, by specifying the refractive power and lens configuration of the four lenses R as described above, the entire lens system can be miniaturized and the zoom ratio can be as high as about 3 to 4. In addition, it is possible to achieve a zoom lens that has good optical performance over the entire zoom range.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the paraxial refractive power arrangement of the zoom lens of the present invention, and FIGS. 2 to 4 are numerical examples 1 to 3 of the present invention, respectively.
5 to 7 are aberration diagrams of numerical examples 1 to 3 of the present invention, respectively. I in the cross-sectional view of the lens
, IT, III, rV are sequentially 1st group, 2n, 3rd group.
The fourth group, arrows indicate the movement direction of each lens group during zooming from the wide-angle end to the telephoto end, and in the lens cross-sectional view, (A) shows the wide-angle end, (B) shows the middle, and (C) shows the telephoto end. In the aberration diagram (A). (B) and (C) are at the wide-angle end, respectively.
Aberration at intermediate and telephoto end, d is d-line, g is g-line, S. C is a sine condition, ΔS is a sagittal image plane, and ΔM is a meridional image plane.

Claims (2)

[Claims] (1) It has four lens groups, in order from the object side: the first group with negative refractive power, the second group with positive refractive power, the third group with negative refractive power, and the fourth group with positive refractive power. When changing the magnification from the wide-angle end to the telephoto end, both the second and third groups are moved toward the object side, and when changing the magnification from the wide-angle end to the telephoto end, the paraxial lateral magnification of the fourth group is changed from the wide-angle end to the telephoto end. A zoom lens characterized in that each element is set so that is always positive. (2) When changing the magnification from the wide-angle end to the telephoto end, when the amounts of movement of the third and fourth groups are M3 and M4, and the amount of movement toward the image plane side is positive, -1<M4/M3<0 .8. The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.