JPS6167016A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To simplify mechanism and easily to obtain a specific variable power ratio by moving two out of three lenses, i.e. the 1st and the 3rd lens groups and fixing the 2nd lens which includes a stop frequently. CONSTITUTION:The 1st lens group is given positive refracting power and the 2nd and the 3rd lens groups are both given negative refracting power to obtain telephoto type lens constitution on the whole, thereby obtaining a zoom lens which, specially, has a short back focus at the wide-angle end and short overall lens length. Then, 0.5fw<1.5fw(1), -2fw<f3<-0.2fw (2), and 0.2fw<e2w<fw (3), where f1 and f3 are the focal lengths of the 1st and the 3rd lens groups, fw is the focal length at a zoom position on the wide-angle end side, and e2w is the principal-point gap between the 2nd and the 3rd lens groups at the zoom position on the wide-angle end side.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compact zoom lens, and particularly to a lens with a total length (first lens length) effective for lens shutter cameras, video cameras, etc.
Related to a small zoom lens with a short distance from the lens surface to the image plane (distance of 1) In recent years, with the miniaturization of lens shutter cameras, video cameras, etc., a zoom lens with a short overall lens length is in demand. Also, in the field of cameras such as lens-shutter cameras in which lenses are not replaced, there is a demand for the attachment of zoom lenses, and there is a demand for compact zoom lenses that are as long as conventional single-focal-length lenses.

For example, in JP-A-56-128911, two lens groups are constructed in order from the object side: a first lens 3p1 having a positive refractive power and a second lens group having a negative refractive power. A small two-group zoom lens that changes the magnification by changing the interval between the two groups has been proposed.

In this proposal, positive and negative refractive powers are sequentially applied from the object side.
By adopting the JIJ structure, a compact zoom lens with a short back focus and a mechanically simple configuration is achieved.

However, with the above-mentioned two-group zoom lens, it is difficult to obtain the desired zoom ratio without moving the lens groups relatively much.
As a result, more aberrations were generated in the front group than in the rear group, and it was difficult to correct the aberration fluctuations at this time in the front group.

Further, in Japanese Patent Application Laid-Open No. 58-184916, the lens is composed of three lens groups, first, second, and third lens groups having positive, positive, and negative refractive powers in order from the object side, and the three lens groups are moved. A three-group zoom lens with variable magnification has been proposed.

This three-group zoom lens has three lens groups that move to change the magnification, so it tends to be mechanically complex.

Furthermore, since both zoom lenses also move the aperture when changing the magnification, the movement mechanism tends to become complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact zoom lens that can easily obtain a predetermined variable power ratio, is mechanically simple, and has a short overall lens length.

The special value of a compact zoom lens to achieve the purpose of the present inventor is that the first lens group has a positive refractive power of 1@ from the object side.
It has three lens groups: a second lens group with negative refractive power and a third lens group with negative refractive power, with the second lens group being fixed and the first lens group and the third lens # being placed on the object side. The magnification was changed by moving the image to .

Therefore, in the present invention, two of the three Fi lens groups, the XS8ga lens group, are moved, and the second lens a+t-, which often includes an aperture, is fixed, thereby simplifying the mechanism.

FIG. 1 shows a schematic diagram of the optical character arrangement of one embodiment of the present invention.

In the figure, 1, 1.1 are the 11th, second, and third lens groups, respectively, and the arrows indicate the movement directions during zooming.As shown in Figure 1, in the present invention, the first lens group is Both the second and third lens groups have negative refractive power, and the overall lens structure is of a telephoto type, achieving a zoom lens with a short back focus and a short overall lens length, especially at the wide-angle end.

That is, when the present invention is applied to a camera with a lens-shutter set, it is compact and convenient to carry if the camera is stored in the wide-angle end when carried. For this reason, the total length of the lens at the wide-angle end is made as short as possible.In addition, in the present invention, the distance between the second and third lens groups is made closer at the telephoto end than at the wide-angle end to achieve a more telephoto lens. The overall length of the lens has been shortened even at the telephoto end.

Furthermore, in the present invention, at the wide-angle end, the distance between the rear principal point of the first lens group and the front principal point of the second lens group is ``IW''. The interval "2W" is longer, and at the telephoto end, the rear principal point of the first lens group and the second
The distance between the front principal points of the lens group "IT" The distance between the rear principal point of the second lens group and the front principal point of the third lens group 6□T is shorter than that of the refractive power arrangement, which reduces aberrations in a well-balanced manner. Corrections are being made.

In the present invention, it is preferable to satisfy the following conditions in order to reduce aberration fluctuations over the entire magnification range and shorten the overall zoom lens.

The focal lengths of the first and third lens groups are f, f3, and f3, respectively.
When the focal length at the wide-angle end zoom position is /w and the principal point interval t''zw between the second lens group and the third lens group at the wide-angle i zoom position, α5/w<7.<1. 5]'W ---...fi
l-2fw< /3 < -0,2/W -----
−= (2+α2 fw< 112W < fyy
・If the condition of −+3+ is satisfied, then it will fail.

In order to shorten the total lens length in a telephoto lens configuration, the refractive power of the first lens group having positive refractive power may be increased. However, if the refractive power of the first lens group is set too large, the refractive power of the third lens group is 4J! The value increases in the direction of L, the Petzval sum increases in the negative direction, the curvature of field becomes overcorrected, and the flatness of the image surface is lost.

Therefore, in order to obtain good depiction performance, K is such that in the lens configuration described above, the focal length f1 of the first lens group and the focal length f3 of the third lens satisfy conditional expressions (1) and (2), respectively. If the lower limit of conditional expression (1) is exceeded, or the upper limit of conditional expression (2) is exceeded, the overall lens length will be shortened, but the field curvature will be overcorrected over the entire variable region, resulting in an image distortion. The flatness of the surface is lost.

Furthermore, if the upper limit of conditional expression (1) is exceeded or the lower limit of conditional expression (2) is exceeded, the total length of the lens becomes long, and aberration fluctuations during zooming become large, which is undesirable.

Furthermore, in the zoom lens of the present invention, by moving the third lens group toward the object side, L is multiplied, and the resulting electrification of the image plane position is corrected by moving the first lens group toward the object side. Since the lens is profitable and successful, it is necessary to make the distance e2w somewhat wide at the wide-angle end. However, if the distance e2w is made too wide, the image plane position will come into contact with the third lens group, which is not preferable. In other words, if the upper limit of conditional expression (31) is exceeded, the third
Because the lens group is too close to the image plane, the lens configuration is not suitable. If the lower limit is exceeded, it becomes difficult to efficiently change the magnification, and as a result, the total length of the lens becomes longer.

In order to achieve good aberration correction while simplifying the lens configuration in the present invention, in order from the object side, the first lens # has four lenses with positive, negative, positive, and positive refractive powers, and the second lens
The lens group is configured to have a laminated lens or a single lens with positive and negative refractive powers, and the third lens group is configured to have at least 41 meniscus-shaped lenses with negative refractive powers with convex surfaces facing toward the image plane side. It is preferable to do so.

In the present invention, focusing is preferably performed by moving the first lens group in order to correct aberrations, but it may also be performed by moving the second lens group or by moving all lens groups.

As described above, according to the present invention, it is possible to achieve a compact zoom lens that is mechanically simple and has a short overall lens length that allows a predetermined variable power ratio to be easily obtained.

Next, numerical implementation sequences of the present invention are shown. R in the numerical implementation sequence
1ii radius of curvature of the first V-lens surface in order from the object side,
Di is the first one from the object side.

The lens thickness and air gap, N1 and νl are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Numerical implementation sequence I F-100-125, 3FNO-1: 3.5-4.5
261-56. r~4a6'R1-46,37D 1=
10.98 N l-1,69680v 1-5
5.5R2-127,99D2-! 1L70 R3= -49,72D 3-2.50 N>
1.68893 & 2-31.1R4-131,74
D 4-136 R5--19 & 99 D 5-IL 74
N 3-1.60729 ν 3-49.2R
6--41,1606-1,17 R7-76,20D7-6.86 N4-1.5
8913 ν44LOR8--555, 5108-1,
58~49.64R9-Aperture 9D λ59 RIO-1105,63DIO-6,24N 5-L
67270 ν 5-3L lR11--63,2
5Dll-148N 6-1.80610 Jiro 4α
9R12-131136012-1 & 11~7.22
R13--66,11013-5,06N? -L664
46 ν 7-35.8R14--314,57 Numerical Example 12 F=100-146.5 FNO"l: 15-4
．． 5 2ω-30,2''~21.0'R1=5
& 95 D 1=io, Go N l=1.
58913 v 1=61.0R2 Lord-805,850
2-9,90 R3--5LQ6 D3-L81 N
2-L85026 ν 2-32.3R4-50&
35 D4-5.23 R5--5476 & 86 D 5-6.49
N 3rd class L 51118ν3-5LOR6--4L61
D6-29.20 R7-59,7007-6,25N 4-L 5596
3 y 4-6L 2R8--21L79 08-
LO3~34.08R9-Aperture D 9-1.89 gto-30a 99 DIO-163N 5”1.6
7270! 15-3L lR11--3&65 Dl
l-1,83N6 plow 1.80610 v 6-40.9
R12-291,38Di2-15.18~0.97R
13--16α15 013-Z 50
N 7-1.88300 ν 7-40.8
R14-15179Di4-9.73 ais--48,23D15=! 50
N 8-1.88300 y 8-40.8

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the refractive power arrangement of the zoom lens of the present invention, FIGS. 2 and 4 are cross-sectional views of the lens of numerical implementation of the present invention, and FIGS. Figure t (A)
, (B) are various aberration diagrams of the uninvented numerical implementation column 1.2. In the figure, t, u, and llt are the 1S, 2nd, and 3rd lens groups, respectively;
(French) and (B) are lens cross-sectional views and various aberrations at the wide-angle end and telephoto end, respectively [, g d g -1d is the d-line, S and C are sine conditions, △S is the sagittal plane, and 6M is the meridional image. It is a surface.

Claims (1)

[Claims] (1) It has three lens groups, in order from the object side: a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with negative refractive power. . A compact zoom lens, characterized in that magnification is changed by fixing the second lens group and moving the first lens group and the third lens group toward the object side. (2) The focal length of the first and third lens groups is f_1, respectively.
, f_3, the focal length at the wide-angle end zoom position is f_W,
When the distance between the principal points of the second lens group and the third lens group at the wide-angle end zoom position is e_2_W, 0.5f_W<f_1<1.5f_W -2f_W<f_3<-0.2f_W 0.2f_W<e_2_W The compact zoom lens according to claim 1, characterized in that it satisfies the condition <f_W.