JPS62262813A - Zoom lens - Google Patents

Abstract

PURPOSE:To form a lens which is bright and has a high performance, in spite of its compactness, by specifying the focal distances of the front group and the rear group, an interval between the second negative meniscus lens and the third negative lens in the front group, radii of curvature of the front surface and the rear surface of the first positive lens in the front group, and the relation of the Abbe numbers of the second negative meniscus lens and the third negative lens in the front group. CONSTITUTION:The front group has the first positive lens, the second negative meniscus lens whose convex surface has been faced to the front, the third negative lens and other lens in order, and when focal distances of the front group and the rear group, an interval between the second negative meniscus lens and the third negative lens in the front group, radiuses of curvature of the front surface and the rear surface of the first positive lens in the front group, and Abbe numbers of the second negative meniscus lens and the third negative lens in the front group are denoted as FI, FII, and d4, and r1 and r2, and nu2 and nu3, respectively, one or more conditions of inequalities 1-4 are satisfied. By satisfying said conditions, a zoom lens which is compact and bright, and has a high performance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a bright and compact zoom lens, and is also suitable as a photographing lens for a video camera.

[Conventional technology]

Conventionally, a four-group zoom lens has been commonly used as a zoom lens for video cameras. This has the advantage of increasing the zoom ratio, but on the other hand, it is difficult to make it compact. In addition, in order to shorten the shooting distance, it is necessary to take in sufficient amount of peripheral light, but this requires increasing the diameter of the front lens, which again works against miniaturization.

Therefore, in the present invention, a two-group zoom lens is used to make it more compact, but this invention
For two-group zoom lenses known from Publication No. 3 and other publications, a lens with an F number darker than 2.0 is considered lucky. □ [Problems to be solved by the present invention] The present invention aims to solve the problems of the prior art and provide a compact, yet bright and high-performance lens.

In order to achieve the above object, in a zoom lens that performs zooming by mechanically changing the distance between the front group I having a negative composite refractive power and the rear group ■■ having a positive composite refractive power,
The front group has, in order, a positive first lens, a negative meniscus second lens with its convexity facing forward, a negative third lens, and other lenses, and the focal length of the front group is FI, and the focal length of the rear group is FH1.
The distance between the negative meniscus second lens and the negative third lens in the front group is d4, the radius of curvature of the front and rear surfaces of the positive first lens in the front group is r1 and r2, respectively, and the negative meniscus second lens in the front group is and the Abbe numbers of the negative third lens are ν2 and ν3, respectively, and one or more of the following conditional expressions shall be satisfied.

(1) 0.6<FII/|FI|<0.9(2)
0.2<d4/IFII<0.4(3)-1,1<
(rl-r2)/(rl+r2)<-0,5, and the lens following the negative third lens is a positive lens with its convexity facing forward,
In particular, a meniscus-shaped positive lens is desirable. The rear group is positive;
A lens configuration with negative and positive power as the basic power arrangement is adopted, and in the embodiment, a biconvex positive lens, a positive meniscus lens with the convex facing forward, a biconcave lens, and a biconvex lens are sequentially arranged.

The meaning of the above conditional expression will be explained below.

Conditional expression (1) expresses an appropriate power distribution between the front group and the rear group in order to achieve a lens combination of I and aberrations maintained well. If the lower limit of conditional expression (1) is exceeded, the power of the front group relative to the rear group becomes weaker, and the mobile acid of the front group increases during zooming, resulting in an increase in the overall length of the lens on the wide side, and as a result, the front lens becomes weaker. The diameter must also be increased, which impairs the compactness of the lens.

If the upper limit of conditional expression (1) is exceeded, the power of the front group becomes too strong relative to the power of the front group, and the aberrations associated with the divergent power of the front group cannot be corrected by the rear group alone, and the Petzval sum becomes too small. Astigmatism cannot be removed. Moreover, negative distortion on the wide side also increases.

Conditional expression (2) is a condition for correcting aberrations in the front group and suppressing the curvature of field on the wide-angle side and the bulge of specular aberration on the telephoto side in a well-balanced manner. The spherical aberration of the lens disappears, but the curvature of field on the wide-angle side becomes severe, and the field becomes sharply undersized at high angles of view.

On the other hand, when the upper limit of conditional expression (2) is exceeded, the curvature of field on the wide-angle side becomes easier to correct, but the bulge of spherical aberration on the telephoto side increases. Also, number 1. The outer diameter of the second lens is also large, which is against the need for compactness.

Conditional expression (3) is a parameter that determines the shape of the first lens in the front group.If this parameter exceeds the lower limit, negative distortion at the wide-angle side cannot be corrected, and if it exceeds the upper limit, the image plane at the wide-angle side will It becomes impossible to correct the tilting of the head.

Conditional expression (4) restricts the number of glass materials for the second and third lenses in the front group; if this condition is exceeded, the fluctuations in each chromatic aberration due to zooming will become too large.

By satisfying the above conditions, it is possible to obtain a compact, bright, high-performance zoom lens with a small number of constituent elements.

Examples are shown in Tables 1 to 3 below.

Table 1 (Example 1) f=8.3-16. OF, No, = 1: 1.7-2.
1 side No. Radius of curvature r Thickness interval d n
d vdl 58.71 3.
4 1.60311 60.72 1209
．． 90 0.2 3 23.82 1.3 1.8061
0 40.94 10.17 6.
55 -124.15 1.1 1.772
50 49.86 18.07 1.5 7 17.50 3.0 1.8051
8 25.4859.85 <Variable> 9 Narrowing> 1. O 1o 25.65 4.5 1.6
2299 58.211 -35.87
0.2 12 11.28 3.9 1.71
300 53.813 56.41 0
．． 7 14 -72.48 5.0 1.846
66 23.915 7.95 2
．． 016 16.26 4.5 1.
77250 49.617 -23.46
0.5 18 cx) 1.0 1
．． 53800 60. O190° fI = -21,02 flI = 16.37 Table 2 (Example 2) f = 8.3-16 F, No, = 1: 1.7 ~
2.1 Surface No., radius of curvature r, wall thickness interval d
nd vdl 67.72
3.30 1.62041 60.32-210
9.14 0.20 3 25.94 1.09 1.7859
0 44.24 10.75 6.50 5 -78.95 1.00 1.7880
0 47.46 17.19 1.41 7 18.56 2.94 1.8051
8 25.48 133.49 <Variable> 9 29.72 4.46 1.6180
0 63.410 -26.90 0.2
011 10.51 4.05 1.69
680 55.512 33.91 0
．． 67513 -92.15 5.06 1
．． 84666 23.914 7.855
2.2315 17.03 5.01
1.78800 47.416 -24.5
8 1.0017oo 5.
00 1.51633 64.118c11) fI=-21,03 fII=16.51 Table 3 (Example 3) f-8,3-16,0F, No, =1: 1.7-2.
1 side No., radius of curvature r, wall thickness interval cl
nd vdl 63.43 3
．． 50 1.61700 62.82-4642
．． 53 0.15 3 26.77 1.25 1.7995
2 42.24 10.89 6.58 5 -86.83 1.18 1.7865
0 50.06 18.60 1.41 7 18.23 2.99 1.8051
8 25.48 128.45 <Variable> 9 Narrowing> 1.00 10 29.20 4.61 1.620
41 60.311 -27.96 0.
1512 10.73 3.97 1.6
9680 56.513 34.49
0.6614 -91.25 5.27 1
．． 84.666 23.915 8.03
7 2.1316 16.93 4,74
1.78650 50.017 -24.
55 1.0018 ■ 5.00
1.51833 64.119 o
.

fI=-21,02 fII=16.50 Table 4 shows the values of each conditional expression in the claims for each embodiment.

Table 4

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens according to an embodiment of the present invention. FIG. 2 is a longitudinal aberration diagram at the wide end and telephoto end of Example 1. FIG. 3 is a longitudinal aberration diagram at the wide end and telephoto end of Example 2. Figure 4 shows Example 3
Longitudinal aberration diagrams at the wide end and telephoto end. In the figure, ri is the lens surface, di is the distance between the lens surfaces, S is the sagittal focal line, and M is the meridional focal line. Keiqz Gacoccus u7 difference i U, knowledge Z collection distortion Goki storage distortion

Claims (1)

[Claims] (1) In a zoom lens that performs zooming by changing the distance between a front group having a negative composite refractive power and a rear group having a positive composite refractive power, the front group is a positive first lens. , a negative meniscus second lens, a negative third lens, and a positive lens with the convex side facing forward, the focal length of the front group is FI, the focal length of the rear group is FII, and the negative meniscus lens in the front group is The distance between the second lens and the negative third lens is d_4, the radius of curvature of the front and rear surfaces of the positive first lens in the front group is r_1 and r_2, respectively, and the distance between the negative meniscus second lens and the negative third lens in the front group is When the numbers are ν_2 and ν_3, respectively, (1) 0.6<FII/|F I |<0.9 (2) 0.2<d_4/|F I |<0.4 (3) -1. 1<(r_1-r_2)/(r_1+r_
2) A zoom lens that satisfies <-0.5(4)45<(ν_2+ν_3)/2. (2) The zoom lens according to claim 1, wherein the front group has a four-element structure including a positive meniscus lens with a convex surface facing forward after a negative third lens. (3) The zoom lens according to claim 1, wherein the negative third lens in the front group has a biconcave shape. (4) The zoom lens according to claim 1, wherein the rear group includes a plurality of positive lenses, a negative lens, and a positive lens in this order.