JPH0478809A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain the zoom lens which is composed of a relatively small number of elements and made compact and has a high power variation ratio and high performance by composing the lens system of five lens groups and fixing 1st, 3rd, and 5th groups during power variation. CONSTITUTION:The zoom lens consists of the 1st lens group which has at least one negative lens and one positive lens and is fixed during the power variation, a 2nd negative lens group which moves as the power is varied, the 3rd positive lens group which consists of a single lens having an aspherical surface and relatively weak refracting power and a positive single lens and is fixed during the power variation, a 4th positive lens group which corrects a shift in image plane position due to the power variation, and the 5th lens group which consists of a single lens with relatively weak refracting power and is fixed during the power variation. Consequently, the zoom lens which is compact and has excellent performance although the lens has a >=X6 high power variation ratio can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a compact zoom lens suitable for video cameras and the like.

(Prior Art) In recent years, with the spread of home-use integrated video cameras, various lenses for video cameras have been actively developed. Among these zoom lenses, as seen in JP-A-62-24213 and JP-A-63-123009, there are zoom lenses that have a high zoom ratio of 6x or more, with positive, negative, Consisting of four lens components each having positive and positive refractive powers, the magnification changing middle lens component and the third lens component are fixed, the second lens component is moved in one direction to perform the magnification change, and the fourth lens It is known to correct fluctuations in focal position due to zooming by moving components back and forth.

This type of zoom lens is known as a type with a relatively small number of lenses despite its high zoom ratio and large aperture, and because the third lens component does not move when changing the magnification, the distance between the second lens component and the aperture is limited. It is possible to shorten the length, and the diameter of the front lens can be made relatively small. However, when further downsizing and increasing the magnification ratio are carried out, the performance inevitably deteriorates. In particular, distortion and astigmatism increase.

(Problems to be Solved by the Invention) The present invention is constructed with a relatively small number of sheets and can be made lightweight and compact.
The object of the present invention is to obtain a zoom lens with a high zoom ratio, particularly a zoom lens suitable for use in a high-performance video camera.

(Means for Solving the Problem) The zoom lens of the present invention has at least one negative lens and one positive lens in order from the object side, a positive lens group that is fixed when changing the magnification, and a positive lens group that moves as the magnification changes. a negative second lens group that has a relatively weak refractive power with an aspherical surface, and a positive single lens that is fixed during zooming, and a positive third lens group that is fixed during zooming; the image plane position changes with zooming. The positive fourth correcting
The lens group is composed of a single lens having relatively weak refractive power, and is characterized by being composed of a fifth lens group that is fixed during zooming.

Furthermore, it is desirable that the following conditions be satisfied as a secondary condition.

In the second lens group, 0.2<lf, IF, i/(f, Z)<0.4 (
1) fo: focal length of the entire lens system at the wide end f2: second
Focal length of lens group F-: F-number at wide end Z: Zoom ratio -0,18<fU/f3A<O,1,8(2)0. 00
1<FN△, /fw<0.1 (3) However, fl: Focal length of the entire lens system at the wide end f3A = 3rd
Focal length of a single lens having an aspherical surface in the lens group Fo: F number at wide end △: Amount of deformation of the aspherical surface of the third lens group from the child spherical surface at the effective radius position In the fourth lens group, 0. 3<fN/f, <0.7 (4) However, fw: Focal length of the entire lens system at the wide end f4: Fourth
Focal Length of Lens Group It is also desirable that the fourth lens group has at least one positive lens and one negative lens.

-0,20<fw/f,<0.20 for a single lens in the fifth lens group (5) However, fw: Focal length of the entire lens system at the wide end f5: Focal length of the fifth lens group; Preferably, the group has an aspherical surface.

(Function) The lens group of the zoom lens of the present invention has at least negative lenses and positive lenses in order from the object side, is fixed during zooming, and has positive refractive power. By having at least one negative lens and one positive lens, magnification and Hosochi chromatic aberration are well corrected. The second lens group has negative refractive power and changes magnification by moving on the optical axis. The third lens group is fixed during zooming and has positive refractive power as a whole, and the single lens with relatively weak refractive power in this lens group has an aspherical surface, which allows the aperture to be Aberrations are corrected,
1) By having a weak refractive power, even if glass materials such as plastics, which are easy to process, are used to reduce costs, changes in performance such as changes in back focus due to environmental changes can be made to a level that does not pose a practical problem. is possible. Further, the positive single lens of the third lens group guides the diverging light flux from the second lens group to the fourth lens group as almost afocal. The fourth lens group has a positive refractive power, and moves in response to changes in the image plane position caused by changing the magnification by the second lens group, thereby correcting the changes.

Furthermore, focusing in the present invention is possible using the lens group, the third lens group, the fourth lens group, etc.
Since the incident light to the fourth lens group is almost afocal, changes in aberration due to movement of the fourth lens group are relatively small, and it is advantageous to perform focusing with the fourth lens group in terms of performance and compactness. It is.

The fifth lens group is composed of a single lens with a relatively weak refractive power that remains fixed during zooming, and by placing it near the image plane, it eliminates astigmatism and distortion without having a large effect on other aberrations. This enables good correction of aberrations. Further, the fifth lens group has relatively weak refractive power. If the fifth lens group has positive refractive power, and if the imaging magnification (reduction system) of the fifth lens group is m5, then the amount of movement of the fourth lens group when changing magnification is 1/m for changes in surface position
, increases in proportion to the square of . For this reason, if the fifth lens group has a positive and strong refractive power, the amount of movement of the fourth lens group will be large, and the space for movement will become large, making it difficult to make the entire lens system compact. If the fourth lens group is used as a focusing lens, there is a possibility that it will interfere with the third lens group, which is not preferable. In addition, if the fifth lens group has a strong negative refractive power, the amount of movement of the fourth lens group will be small, and negative distortion on the wide side can be reduced, which is advantageous for compactness. It becomes difficult to satisfactorily correct spherical aberration due to the increase in the refractive power of the fourth lens group.

Preferably, the fifth lens group has an aspherical surface, which is effective in correcting aberrations, and particularly astigmatism at large angles of view can be corrected well. Furthermore, since the fifth lens group is located close to the image plane, there is little change in back focus even when using glass materials such as plastic, which have large performance changes due to changes in temperature and humidity. It is possible to use

Condition (1) is a condition regarding the focal length of the second lens group, the focal length of the entire system at the wide end, and the zoom ratio; if the upper limit is exceeded, the amount of movement of the second lens group due to zooming becomes large;
The distance between the first lens group and the third lens group becomes large, making it difficult to make the lens compact.

Moreover, when the lower limit is exceeded, it becomes difficult to correct fluctuations in astigmatism and distortion due to zooming.

Condition (2) is a condition regarding the focal length of the single lens with relatively weak refractive power that has an aspherical surface in the third lens group, and the focal length of the entire system at the wide end.If the upper limit is exceeded, spherical aberration will be insufficiently corrected. If the lower limit is exceeded, spherical aberration will be overcorrected, leading to a decrease in contrast and deterioration of image quality. Furthermore, by satisfying this condition, it becomes possible to suppress changes in back focus when a glass material such as plastic is used.

Condition (3) is a condition regarding the amount of deformation of the aspherical surface of the single lens with relatively weak refractive power that has an aspherical surface in the third lens group, and the focal length and F number of the entire system at the wide end.If the upper limit is exceeded, The error sensitivity to eccentricity of this lens increases, causing a practical problem. Also, if the lower limit is exceeded, spherical aberration,
Correcting coma aberration becomes difficult.

Condition (4) is a condition regarding the focal length of the fourth lens group and the focal length of the entire system at the wide end; if the upper limit is exceeded, extroverted coma aberration increases at large angles of view, leading to a decrease in resolution. If the lower limit is exceeded, the amount of movement of the fourth lens group increases, which is disadvantageous for compactness. Furthermore, it is desirable that the fourth lens group has at least one positive lens and one negative lens in order to suppress the occurrence of lateral aberration.

Condition (5) is a condition regarding the focal length of the fifth lens group and the focal length at the wide end.The problem when the focal length of the fifth lens group becomes small was explained earlier, but especially if this upper limit is If it exceeds the lower limit, negative distortion will increase on the wide side, and if it exceeds the lower limit, the exit pupil will be too close to the image plane.

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

Each symbol in the table is R: radius of curvature of each refracting surface D: distance between refracting surfaces N: refractive index of lens glass material (wavelength is d-line = 587.56
nm) ■ = Abbe number of the glass material of the lens f: Focal length of the entire lens system 2ω: Angle of view F: F number f, 2 Back focus (length from the image side of the cover glass to the image forming surface) ΣD: Lens Length from tip to image plane (including cover glass) Y: Indicates image height. Further, the various values described in this specification for each example are shown in the attached table. In the embodiment, a cover glass corresponding to a low-pass filter, an infrared cut filter, and a face plate is provided between the final lens surface and the imaging surface.

In addition, the specific configuration of the embodiment will be shown below.

From the object side, the lens group consists of a negative meniscus lens and a positive biconvex lens, a positive meniscus lens with its convex surface facing the object side, a negative meniscus lens, a biconcave lens and a positive lens. A second lens group consisting of lenses in this order, a third lens group having a single lens with a weak refractive power having an aspherical surface and a positive single lens, a positive single lens, and a composite lens of a negative meniscus lens and a positive lens. and a fifth lens group consisting of a single lens with relatively weak refractive power.

The definition of the aspheric coefficient in the example is as follows.

ch”
Eighty. h1a+・・・・However, Represents paraxial curvature.

Example 1 f=7.20~41.1111 F=1.84~2
．． 402ω=45.7~8.4 Y=3.03
fb=2.05No RD N
V5'' 44.820 Group spacing f A BC 7,200,7017,204,84 17,608,978,933,39 41,1815,472,437,34 group running Focal length of each group 1 f1~. = 29.4692 f, ~
□. = -7,9493f□, ~,, = 3
0.3384f1. -□, = 14.5705
f, □23 = 218.242 Effective radius of 14th surface = 4.14 Aspheric coefficient 14th surface = 0.75126X10 = 0.20172 x 1O-3 = 0.10229X10-" = 0.19266X10 = 0.19815X10 -'=-0,24663X10-'=-0,48691X10-" 4.41 5.86 1.91 Example 2 f=7.16~41.17 2ω=45.9~8.4 No R F= 1.84~2.40 Y=3.03 fb=2.05 ■ Group spacing A B 7.16 0.70 17.20 17.59 8.97 8.93 41.1715.47 2.43 Group spacing Focal length of each group 1f□~, = 29.446 2f, . = −7,911 3f1□～,, = 30.7624f,～,,
= 14.7275 f2゜-,, = 24
2.063 Effective radius of 14th surface = 4.1 Aspheric coefficient 4.84 3.39 7.34 4.41 5.86 1.91 14th surface 21st surface = 0.94047X 10 = 0.18717X10- " = 0.11352x10-' = 0.16627X 10 = 0.20017X10-' = -0,24691X1O-s = -0,48691X10-" Example 3 f = 7.20 ~ 41.68 2ω = 45.6 ~ 8.3 No R F =1.84~2.40 Y=3.03 f, =2.12 ■ 7.20 17.63 41.68 Group Eight 0.70 8.97 15.47 Interval 17.20 8.93 2.43 4.84 3.39 7.34 4.41 5.86 1.91 Group Nα Focal length of each group 1 f1~! ; = 28.2062 f,
1o=-7,957 3f engineering, 0. = 35.319 4f□, ~,, = 13.6345 f2゜~
,, =-106,436 Effective radius of 14th surface = 4.
48 Aspheric coefficient 14th surface K = 0.11381x102A4=
0.23706 x 1O-3A, = 0.10552
X 10-5 21st surface K = 0.57621X
10A, = 0.15310 x 1O-3AG = -0
,23720x to-'A,=-0.48691 X 10-''N.

■ Example 4 f = 7.20 ~ 41.12 2 ω = 45.6 ~ 8.4 F = 1.84 ~ 2.40 Y = 3.03 ft, = 2.05 Group spacing A B 7.20 0.70 17,20 17.62 8.97 8.93 41.1215.47 2.43 Archipelago Focal length of each group 1f□~5 = 29,770 2 f, 1° = -7,943 3f□□ -,, = 29.053 4 fl,,, = 14.9825 f2.
．． 3 = 69.994 Effective radius of the 14th surface = 4.12 Aspheric coefficient for the 14th surface = 0.82075 x 104.84 3.39 7.34 A4 = 0.20181X 10-” 21st surface K = - 0,49388 A, = 0.13384 X 1O-3A, = -0,2
5956X 10-' A, = -0.48691 .84~2.88 y = 3.03 f , = 2.00 [)
N V A, = 0.10027x 10-'11] 3rd 12.997 1.60 1.49200 57.0 3 f11~1 = 35.429 4th 189.706 1.90 Group spacing A B 6. 70 0.70 19.40 1g, 22 9.83 10.22 51.1717.70 2.40 Group Arashi Focal length of each group 1 f,, = 30.9872 f, ~,
. = -7,3731,77250 6,73 3,75 9,85 4f15-□, = 18.27349.6 5 f,, 23 = 94.408 Effective radius of 11th surface = 4.99 Aspheric coefficient 11th Surface K = -0,33358X 10A, =
0.65702 X 10-'21st surface K =-0
,44664X 10A4=-0°10191 x 1
0-'A, =-0.10643
5.71ΣD 61.05 61.05 61
．． 11 61.05f2IFw/(fwZ) 0.3
2 0,35 0.35 0.36fw/f3A
O,000,13-0,100,01Fw△,/fw
O,030,020,040,02fw/f40
．． 49 0.49 0.53 0.48fw/f
-0,030,03-0,070,10 Example 5 7.64 68.50 0.27 0.00 0.0 0.37 0.07 (Effect of the invention) The zoom lens of this invention As seen in the examples and drawings, we were able to realize a zoom lens that has a high zoom ratio of about 6x or more, is compact, and has good performance as seen in each aberration diagram.

[Brief explanation of drawings]

FIGS. 1 to 5 are cross-sectional views of the first to fifth embodiments of the zoom lens of the present invention, and FIGS. 6 to 20 are cross-sectional views, respectively.
The figures are aberration diagrams at wide, middle, and telepositions of the first to fifth embodiments of the zoom lens according to the invention. Diagram

Claims (1)

[Claims] In order from the object side, a positive first lens group has at least one negative lens and one positive lens, and is fixed during zooming;
It consists of a negative second lens group that moves with zooming, a single lens with an aspherical surface and a relatively weak refractive power, and a positive single lens,
It consists of a positive third lens group that is fixed during zooming, a positive fourth lens group that corrects changes in the image plane position due to zooming, and a single lens with relatively weak refractive power. A zoom lens characterized by being composed of five lens groups.