JPH02143213A - Zoom lens - Google Patents

Abstract

PURPOSE:To correct the aberration of a zoom lens in a balanced state with a less number of lenses by constituting the 1st lens group of a negative meniscus lens with a convex surface on the object side and positive lens and the 3rd lens group of a single lens. CONSTITUTION:This zoom lens is constituted of, from the object side, the 1st lens group which is not moved at the time of zooming and has positive refracting power, 2nd lens group which is moved at the time of zooming and has negative refracting power, 3rd lens group which is also moved at the time of zooming and has positive refracting power, and 4th lens group which is not moved at the time of zooming and has positive refracting power. The 1st lens group is composed of a negative meniscus lens with a convex surface on the object side and a positive lens, and the 3rd lens group is composed of a single lens. Therefore, a zoom lens which is sufficiently long in back focus, well corrected in aberration, and has a variable power ratio of about 2 can be constituted of a less number of lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a zoom lens having a four-group configuration, and particularly to a compact and simple-configured zoom lens suitable for video cameras and the like.

(Prior Art) In recent years, various video cameras and still video cameras have been developed, but in order to reduce the cost of cameras, there is a need for a compact zoom lens with a simple configuration.

-S, as a zoom lens with a magnification ratio of about 2x, a two-group zoom type is often used in order to make the camera more compact. Many examples can be found in JP-A-262813 and the like.

However, although this type of zoom lens is compact with a small number of lenses, the lens group that moves during focusing also moves during zooming, which complicates the lens barrel mechanism and increases costs. Another disadvantage is that the F value changes during zooming.

Furthermore, when trying to use this type of zoom lens on a video camera or still video camera, it is necessary to place a low-pass filter, color filter, etc. in front of the image sensor for the video camera or still video camera. This requires a long back focus, but since the overall length of this type of lens differs between the wide-angle end and the telephoto end, attempting to secure a long back focus often involves increasing the size of the lens system.

Examples of three-group or four-group type zoom lenses with a variable power ratio of about 2x are disclosed in Japanese Patent Laid-Open Nos. 127321-1982 and 143311-1980. However, in JP-A-54-127321, one of the lens groups that moves during zooming also moves during focusing, which complicates the lens barrel mechanism. In the embodiment, since the number of lenses exceeds 10, the cost is high. Also, JP-A-58-14
Lens No. 3311 achieves a variable power ratio of 2x with a small number of lenses, but since the first group moves during zooming, the overall length of the lens changes with zooming, making the lens barrel mechanism more complicated. invite.

(Problems to be Solved by the Invention) The present invention enables a simple lens barrel mechanism by performing focusing and zooming using separate lens groups.
The objective is to realize a zoom lens with a zoom ratio of about 2x, which has a sufficiently long back focus and is well corrected for aberrations, using a small number of lenses.

(Means for solving the problem) The zoom lens of the present invention has, in order from the object side, a first lens group having a positive refractive power that remains fixed during zooming, and a first lens group having a negative refractive power that moves during zooming. A zoom lens system comprising a second lens group, a third lens group having a positive refractive power that moves during zooming, and a fourth lens group having a positive refractive power that remains fixed during zooming, the zoom lens system comprising: a second lens group; The first lens group includes a negative meniscus lens with a convex surface facing the object side and a positive lens, and the third lens group is a single lens.

Furthermore, it is desirable that the following conditional expression be satisfied.

(1) 0.35< ci, /ν, < 0.5
0(2) 4.0 < f 0/ f w < 4.
9(3) -1,5< f, /fH<-0°7(4,
) 1.1 < f, /f goes 1.8 where ν2 is the equivalent Abbe number of the glass of the lens constituting the second lens group,
That is, when the total refractive power of the second lens group is φ, and the refractive power and Abbe number of the first single lens in the second lens group are ψi and ν1, respectively.

The value obtained by v2-φ/Σφ1 is shown. In addition, ν is the Atsube number of the single lens that is the third lens group, f4, f2, and f4 are the composite focal lengths of the fil lens group, the second lens group, and the fourth lens group, and f is the wide-angle end. represents the focal length of the entire system.

(Function) In this zoom lens, when zooming from the wide-angle end to the telephoto end, the second lens group moves monotonically from the object side to the image side, and the third lens group also moves from the object side to the image side. 6 Zooming and focusing are performed in separate lens groups, and the overall length does not change due to zooming.A zoom lens moves the first or fourth lens group during focusing. , a type in which the second lens group and the third lens group are moved during zooming is common. However, in such a four-group zoom, it is difficult to reduce the number of lenses due to the nitric acid content, and the cost tends to be high.

In the present invention, achromatization is not performed for each group.

By achromatizing only the entire system, especially the second lens group,
Conditional expression (1) realizes a zoom lens with a sufficiently long puncture focus by reducing the number of lenses in the third lens group and using a negative lens as the lens closest to the object in the first lens group. is mainly used to satisfactorily correct lateral chromatic aberration.If the upper limit of conditional expression (1) is exceeded and the Atsube number of the third lens group becomes too large compared to the equivalent Abbe number of the second lens group Fluctuations in lateral chromatic aberration occurring in the two lens groups due to zooming become large, and it becomes difficult to correct this well. Furthermore, if the lower limit is exceeded and the equivalent Abbe number of the second lens group becomes larger than the Abbe number of the third lens group, the variation in lateral chromatic aberration occurring in the third lens group due to zooming becomes large, and this can be effectively corrected. It becomes difficult to do so.

Conditional expression (2) relates to the focal length of the first lens group; if the focal length of the first lens group becomes longer than the upper limit, it becomes difficult to make the entire system compact, and the distortion becomes large on the negative side. I don't like it. Furthermore, if the lower limit is exceeded, it becomes difficult to correct aberrations, especially at the telephoto end.

Conditional expression (3) relates to the focal length of the second lens group, and when the focal length of the second lens group becomes longer than the upper limit,
The amount of movement of the second lens group during zooming increases,
This prevents the overall lens from becoming more compact. Moreover, if the lower limit is exceeded, the 8-movement amount of the second lens group becomes small and compactness can be achieved, but it becomes difficult to correct aberrations especially at the wide-angle end, which is not preferable.

Conditional expression (4) relates to the focal length of the fourth lens group.If the focal length becomes longer than the upper limit, it is advantageous in terms of correcting the 5 aberrations, but the diameter of the aperture disposed in front of the fourth lens group is If the lower limit is exceeded, spherical aberration will be insufficiently corrected, which is not preferable.

(Example) Examples of the zoom lens of this invention will be shown below.

Here, f is the focal length of the entire system, r is the radius of curvature of each lens surface, d is the lens thickness or lens spacing, nl: iAi! The refractive index, ν4, indicates the Atsube number. A cover glass is also attached to the image side of the lens system, which is also shown.

Example 1 f=100.0-1.90.6 FNn=2.88
r d n 3rd group 280.027 -1622.373 21.49 1.84666 23.8 "11 199.051 23.64 3.785ri0 44.2 evening, /v2
"0-+115 f-/f w"4,59
f2/fw=-0,91f4/fN=
1.53 Example 2 f=]oO,o~190.3 FNQ: 2.88 "17 3L9gg 27.94 1.6!: 1580 55.5-355
．． 046 1.07,47 Variable interval 100.0 138.2 190.6 12°89 76.14 131.11 30.09 33.15 30.09 I76.25 109.94 58.03 645.580 14.84 [-18 -288,231 10,79 300,949 Variable interval 100.0 137.4 190.3 8.63 75.73 135.24 39.16 39.11 31.16 I79.93 112.88 61. 32 v 3/ v 2 =0.410 f H,/
f +,,=4.98f,/f,=-1,11f,/f
W=1.43 Example; 3 f2 100.0-191.8 FNα=2.88r
d n [River 341.934 16.171.80518
25.4 "18 -281.360 107.78 iIf variable fringe interval 00.0 139.5 191.8 1.0.78 73.2!] 125.02 30.18 33.06 30.13 I72. 44 107.05 58.20 "12 175.777 20.66 1.589i3 61
．． 2294.800 2.16 v3/v2=0.416 f,/fw=4.17f2
/fw=-0,83f,/f,=1.64 Example・
1 r = ioo, o ~ 190.3 FNα = 2.85
r d n + 279.523 12.62 +, 78
470 26.22 1st group 175.0=10 58.
04 Reto-18 []2゜213.041 -213,041 Cover glass ω Variable interval 20.50 1.7=1400 44.832.36 65.37 L51G33 64.15
405.462 10.57 1.69680 55
．． 5"6 2nd group 125.236 16.83100.
0 137.7 190.3 5.87 72.97 132.48 42.65 52.23 42.65 I74.52 91 , 8 , i 117 , 91 shi ] / shi 2 - 0.438 f , / f w =4.73 f, /f w=-1,39 f4/f, =1,26 Example 5 f=100.0~HJ0.3 188.004 2683.403 294.766 2nd group 122.075 1g4 ,565 91.855 3rd group 114. =132 143.107 11 251.046 12 -1141.384 13 1st group 338°481 14 -70,553 15 -265,309 FNQ=2.85 37.11 1.71300 10.57 1.69680 16.83 9.78 1.69680 18.00 1.80518 53.9 55゜5 55.5 25.4 ノS8.64 1.76200 40.113.0
9 31.30 1.69680 55.59.39 +
, 8051.8 25.410.79 1.80518
25.4 Variable interval f a b cloo, 0
5.87 42.65 174.52137.
7 12.91 52.2:i 97.841
．． 90.3 +32.48 42. ．． 65 4
7°91 sha, / shi, = 0.439 f, / f,
=4.76f2/fw=-1,39f,/f
W = 1.35 (Effects of the Invention) As is clear from the embodiments and drawings, the zoom lens of the present invention achieves well-balanced aberration correction with a small number of lenses, 8 or 9. 1. It was also compact, and because the movable lens group for zooming and the movable lens group for focusing were separated, the lens barrel structure could be easily made, making it possible to create a highly practical zoom lens.

[Brief explanation of the drawing]

FIGS. 1, 2, 3, 4, and 5 are cross-sectional views of lenses of Examples 1 to 5, respectively.

Claims (1)

[Claims] In order from the object side, a first lens group having a positive refractive power that remains fixed during zooming, a second lens group having a negative refractive power that moves during zooming, and a second lens group having a positive refractive power that moves during zooming. In a zoom lens system consisting of a third lens group and a fourth lens group having a positive refractive power that remains fixed during zooming,
A zoom lens characterized in that the first lens group includes a negative meniscus lens with a convex surface facing the object side and a positive lens, and the third lens group is a single lens.