JPH02123315A - Zoom lens - Google Patents

Abstract

PURPOSE:To make the title zoom lens light in weight and compact by constituting a fifth group of a front group consisting of two pieces of a positive lens and a negative meniscus lens placed at an air interval on its image side from an object side, and a rear group having one negative lens and two positive lenses. CONSTITUTION:A fifth lens group for forming an image consists of a front group and a rear group, and its front lens is constituted of two lens elements of a positive single lens and a negative meniscus single lens at an air interval in order from an object side, and executes a satisfactory correction of a spherical aberration, a comatic aberration and a chromatic aberration. Also, said lens group is allowed to satisfy the condition of the inequality I. In the inequality I, R1-1 and R1-2 denote a radius of curvature of an object side face of the positive lens of the front group and a radius of curvature of an image side face of the positive lens of the front group, respectively. In such a way, although the number of pieces of the lenses is small, each aberration is corrected satisfactorily, and also, the zoom lens being compact and having a large aperture can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens used in video cameras, still video cameras, etc., and particularly to a zoom lens having a large aperture ratio.

(Prior Art) Video cameras and the like have hitherto used zoom lenses with a high zoom ratio of about 6x and a large aperture ratio. An example of this can be found in, for example, Japanese Patent Laid-Open No. 61-93423. However, in recent years, with the rapid spread of video cameras in general households, there has been a desire for zoom lenses to be even lower in cost and weight. reduction, reduce the cost of individual lenses, or make the entire lens more compact.
It is also desired to develop a zoom lens that can be made lightweight.

(Problems to be Solved by this Invention) This invention has a variable power ratio of about 6 times with a large aperture ratio, but it is possible to reduce the number of lens components, making it lightweight, compact, and low cost. The aim is to create a zoom lens that can be used to measure time.

(Means for Solving the Problem) The zoom lens of the present invention includes, in order from the object side, a fixed positive first lens group, a negative second lens group having a variable power function that moves during zooming, and a second negative lens group that moves during zooming. A negative third lens that moves in conjunction with the lens group and has the function of correcting the image plane position.
A zoom lens with a five-group configuration consisting of a lens group, a fixed positive fourth lens group for making the diverging light emitted from the third lens group almost afocal, and a fixed positive fifth lens group for imaging. The fifth group includes a front group consisting of two lenses: a positive lens from the object side and a negative meniscus lens arranged at an air interval from the image side, one negative lens and two positive lenses. The rear group is configured to satisfy the following conditions.

however, R□-□: R1-,: Positive lens in the front group of the 5th lens group radius of curvature of body side Image of the positive lens in the front group of the 5th lens group Side radius of curvature It is.

Also, Delicious.

It is a fixed group.

In this case, the fifth lens group having a positive refractive power must satisfy the following condition: 0×1 rainbow ■−<0.8 (2) ψ.

Y s−z>45 ν5−. (40(3) However, ψ, ": ψ : vs-t: vs-2: Refractive power of the front group of the 5th lens group Refractive power of the 5th lens group Atsube number of the positive lens of the front group of the 5th lens group Atsube number of the negative lens in the front group of the fifth lens group Furthermore, regarding the configuration of each lens group, in order to configure the rear group of the fifth lens group with a small number of lenses and obtain good performance, it is necessary to Positive meniscus lens in order from
It is advantageous to use a triplet type construction, such as a negative meniscus lens, a positive meniscus lens, or a positive biconvex lens, a negative meniscus lens, and a positive meniscus lens.

Further, in order to provide a compact, low-cost zoom lens system with a small number of lenses, it is desirable that the first to third lens groups have the following configurations.

The first lens group consists of three lenses: a negative meniscus lens, a biconvex lens, and a positive meniscus lens.The second lens group consists of a negative meniscus lens with a convex surface facing the object side and a
It consists of a laminated lens of a biconcave lens and a positive lens having a surface with a strong curvature on the object side, and the third lens group consists of a negative meniscus lens with a concave surface facing the object side.

Furthermore, it is desirable that the following conditions be satisfied.

0.1 < fw/f, < 0.4 (4)t
,0<l f21-Ft-z/fr<3.0
(5) 0.1< l fw/fa l <0.3
(6) However, fl: Focal length of the first lens group f2: Focal length of the second lens group f, : Focal length of the third lens group f Category: Focal length of the entire system at the wide end fT: Focal length of the entire system at the tele end Focal length of the entire system Z: Variable magnification ratio (Z = fr/fs) FT: F number at telephoto end (effect) In the zoom lens of this invention, the fifth lens for image formation is
The lens group consists of a front group and a rear group, and the front group consists of two lens elements, a positive single lens and a negative meniscus single lens spaced apart from each other in order from the object side, and prevents spherical aberration and coma aberration. and chromatic aberrations are well corrected, and even when the third lens group or the fourth lens group consists of a single lens as shown in the examples, it is possible to compensate for the resulting lack of aberration correction. There is. This makes it possible to reduce the number of lenses constituting the zoom lens. Further, the rear group consists of one negative lens and two positive lenses, the positive lens having an imaging function, and the negative lens performing good correction of chromatic aberration, distortion, etc.

The first condition (1) is a condition regarding the radius of curvature of the image side surface and the radius of curvature of the object side surface of the positive single lens constituting the front group of the fifth lens group. As seen in the examples, this lens has
The image side surface is a convex surface toward the image side, and if the radius of curvature R0-□ of the object side surface is positive and exceeds the range of this condition, it becomes difficult to correct coma aberration, and extroverted coma flare occurs. This causes a decrease in contrast. Furthermore, if the value is negative and exceeds the range of this condition, it becomes difficult to correct spherical aberration.

Condition (2) is a condition for the substantially afocal light beam emitted from the fourth lens group to be imaged well by the fifth lens group. When the ratio of the refractive power of the front group constituting the fifth lens group to the refractive power of the entire fifth lens group is within the range of this condition, the aberrations generated in the first to fourth lens groups can be effectively suppressed. It is possible to correct it. If the upper limit of this range is exceeded, it becomes difficult to correct one spherical aberration, and the intermediate @ band swells, resulting in a decrease in contrast. Furthermore, if the lower limit is exceeded, the total length of the fifth lens group increases, making it difficult to make it compact.

Condition (3) is a condition regarding the Atsube number of the positive lens and the Atsube number of the negative lens constituting the front group of the fifth lens group,
It is desirable to satisfy this condition in order to enable good correction of chromatic aberration.

Condition (4) is a condition regarding the focal length of the first lens group, and by satisfying this condition, it is possible to suppress the occurrence of aberrations caused by the first lens at a wide angle of view to a range that does not cause any practical problems. Become. If the upper limit of this condition is exceeded, the extroverted comatic aberration of light rays passing through the peripheral portion of the first lens having a large angle of view increases, deteriorating the performance of the peripheral portion of the screen, and overcorrecting spherical aberration. When the lower limit is exceeded, the total length from the first lens group to the fourth lens group increases.

Condition (5) is a condition regarding the second lens group, and by satisfying this condition, negative distortion at a wide angle of view is suppressed, and changes in aberration due to zooming are reduced. If the upper limit is exceeded, the amount of movement of the second lens group for changing the magnification becomes large, which is disadvantageous in reducing the overall length of the lens. If the lower limit is exceeded, the negative power of the second lens group becomes stronger, so the negative increase in the Petzval sum becomes large, and the fifth lens group has a triplet type or a Petzval type as described in this example. It becomes difficult to correct this even if a lens of this type is used.

Condition (6) is a condition regarding the third lens group. By satisfying this condition, the amount of movement of the third lens group, which is a compensator, when changing the magnification becomes small, the movement can be made without interfering with the second lens group, and an increase in the negative Petzval sum is suppressed. Further, it is possible to reduce the burden of aberration correction on the fourth lens group and the fifth lens group. If the upper limit is exceeded, the negative Petzval sum increases and correction becomes difficult, and if the lower limit is exceeded, the amount of movement of the third lens group becomes large, which is disadvantageous for converting to 1-.

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

Regarding condition (1) regarding the radius of curvature of the positive lens in the front group of the fifth lens group, from the viewpoint of actual manufacturing issues and costs, in the case of a biconvex lens where the radius of curvature on the object side and the radius of curvature on the image side are close to each other. It is advantageous to make the absolute values of the radius of curvature the same, and a specific example will be shown in the following examples.

Further, in the zoom lens of the present invention, when a plastic lens is used in order to further reduce costs, it is desirable to use a pair of a negative lens and a positive lens in the fixed part. This is to reduce the influence of environmental changes. In addition, especially when considering manufacturing variations in lenses manufactured by molding, using a molded lens for the moving part may be a major factor in the variations in lens performance. It is better not to use it for moving parts. In addition, it is desirable to arrange the molded lens so that its influence is canceled out by other lenses, or so that the performance-degrading portion is located in the direction of the short side of the screen.

It is also desirable to take this kind of consideration when using a molded lens as a moving part.

Specific numerical examples of embodiments of the zoom lens of the present invention are shown below.

In the table, r is the radius of interest, d is the surface spacing, N is the refractive index, ν is the Atsube number, and the space between the final lens surface and the imaging surface corresponds to a low-pass filter, infrared cut filter, face plate, etc. Contains a cover glass.

Note that SD is the length from the first surface to the final lens surface, fB is the air-equivalent back focus, F is the F number, and ω is the half angle of view.

In addition, for an aspherical shape, the origin is the vertex of the surface, and the optical axis direction is
In the orthogonal coordinate system with the axis as C1, the apex curvature is C1, the conic constant is K, and the aspheric coefficient is A1. When the power of the aspherical surface is PI (P+>2°O), it is expressed as φ=f7.

Example 1 f=9.26~53.22 2ω=52@06’~8″ 1 65.574 2 30.174 3 -75.090 4 26.467 5 97.672 6 115.129 7 11.499 8 -13.521 9 13.709 10 -151.032 11 -21.508 12 -151.529 F　1.44～2.05 48' 1.15 6.00 0.20 3.58 2.80 0.60 2.40 1.80518 1.51633 1.60311 1.77250 1.71300 1.84666 0.70 1.69680 25.4 64.1 60.7 49.6 53.9 23.8 55.5 13 58.028 14 -21.641 15 27.500 16 -27.500 17 -14.161 18 -39.546 19 -50.000 20 -11.136 21 38.064 22 10.231 23 11.150 24 74.435 25 Cover 26 Glass ψ Aspheric coefficient Page 20 ni= A1= A2= A3= -7,29437X10-” -7,02150X10-' -1,55514X 10-' -5,64716X 10-” 3.55 7.12 4.00 1.35 0.95 8.41 4.00 0.60 1.40 4.61 4.00 3.40 7.33 1.71300 53.9 1.71300 53.9 1.84666 23.8 1.49200 55.0 1.58700 30.0 1.58913 61.2 1.51633 64.1 power number P1=4. ooooo.

P 2 : 6.0000 P 3 = 8.0000 On the 22nd side = AI = A2 = A3 = 9.26 22.16 53.22 4.05504 10 -5.54751 1.67 0.38 fB=12.232 f1=38.11 f2=-9,76 f, knee 36.05 f4=22.53 f,=24.27 SD=79.99 φsF/ψ,= 0.41 1 R5-5/ Rs-x I ” 1 Yas-z =
53.9 s-z = 23.8 f w/ f 1 = 0.24 1 f21・F d・Z/f□=2.16 1 f, / f, l=0.257 Example 2 f=9 .26~53.22 Fl, 44~2.05 2ω=52604' ~8@ 64.986 30.068 -75.264 26.491 97.081 11g, 944 11.456 -13.502 13.628 - 141.138 -21.566 -151.493 59.569 -21. , 511 30.000 -25.405 1.15 6.00 0.20 3.58 0.65 2.80 0.60 2.40 0.70 3.55 6.33 4.00 1.35 1. 80518 1.51633 1.60311 1.77250 1.71300 1.8/1666 1.6968<1 1.71300 1.71300 25.4 64.1 60.7 49.6 53.9 23.8 55.5 53.9 53.9 17 -14.062 0.9518
-38.239 8.9419
-50.000 4.0020 -11.
259 0.6021 38.286
1.4022 10.250 4.4
623 11.058 4.0024
74.657 3.4025 Cover (X) 7.3326 Glass ω Aspheric coefficient on the 20th surface = A1 = A2 = A3 = 22nd surface K := 4.36205 X 10-”A 1
= 2.80918 x 10-'p, 2:
7,10375 x 10-”-7,10944X 1
0-"-7,02151x10-'-1,55514X10-" -5,64716x 10-1':' 1.84666 23.8 1.49200 55.0 1.58700 30.0 ],,58913 61.2 1.51633 64.2 Power P 1~4.0000 P 2~6.000 (I P 3~8.0000 P 1~4.0000 P 2~6.0000 A3= -5,54751x 10-" P 3~8.0OO0 9,26 22,16 1,3 12,838 53,22 19,9 f, ~12,226 f = 38.12 f2 = -9,76 f3 = -36,17 f 4 = 22.58 f, = 24.28 Example 3 f = 9.27 ~ 53.22 2ω = 52° 04' ~ 8° 71.192 30.146 b c 19.35 1.3 5.075 4.037 1.67 0.38 SD=79.61 ψ5F/φ, =0.41 1R,, /R,, l=0.81 sis-i ~53.9 ν5+3 ~23.8 f, /f, ~ 0.24 f2 ・Fl・Z/ft=2.16 fW/f, l=0.256 F 1.44~2.05 48' 1.15 6.00 n ν 1.80518 25.4 1.51633 64.1 -74.924 26.410 118.303 111.104 11.556 -13.604 13.615 -175.141 -21.498 -151.529 78.629 -19.157 47.918 -44 .321 -15.083 -30.956 72.338 -23.205 18.865 10.151 0.20 3.58 0.65 2.80 0.60 2.40 0.70 3.75 1.05 3.42 2.46 1.07 13.52 3.96 0.21 1.07 4.47 1.60311 1.77250 1.71300 1.84666 1.69680 1.71300 1.71300 1.80518 1. 62299 1.84666 60.7 49.6 53.9 23.8 55.5 53.9 53.9 25.4 58.2 23.8 12.860 288.585 Cover ψ Glass ■ 9.27 22.17 53.22 1.30 12.838 19.90 fB=14.603 f1=37.88 f,=-9,77 f,=-36,03 f4=21.96 f,=24.57 4.71 2.14 9.80 1.62299 1.51633 58.2 64.1 b c 19.35 1.30 5.075 4.037 1.67 0.38 SD=79.72 ψsr/ψ, =O, tS IR,, /R,11=0.925 s-z =53.9 s-z =25.4 f poetry/f engineering=0.24 f, l・Fl・Z/fr=2.2 1f/f, I=0.263 (Effects of the Invention) As seen in the examples and drawings, the zoom lens of the present invention has a small number of lenses, but each aberration is well corrected. Moreover, it was possible to obtain a compact and large-diameter zoom lens.

In addition, when focusing is performed in the zoom lens of this invention, the focusing element disposed on the imaging plane or the whole of any one of the first lens group, third lens group, fourth lens group, and fifth lens group is used. Or, it can be done by moving a part of it.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 show Example 1 of the zoom lens of the present invention, respectively. Example 2. Each cross-sectional view of Example 3,
Figures 4, 5, and 6 are for Example 1, Figures 7, 8, and 9 are for Example 2, and Figures 10, 11, and 12 are for Example 3. They are various aberration diagrams at a wide-angle end, an intermediate portion, and a telephoto end, respectively.

Claims (1)

[Claims] In order from the object side, there is a fixed positive first lens group, a negative second lens group with a variable power function that moves during zooming, and an image plane that moves in conjunction with the second lens group during zooming. A negative third lens group that has the function of correcting the position, a fixed positive fourth lens group that makes the diverging light emitted from the third lens group almost afocal, and a fixed positive fourth lens group for imaging. A zoom lens having a five-group configuration consisting of five lens groups, wherein the fifth lens
The group consists of a front group consisting of two lenses: a positive lens from the object side and a negative meniscus lens placed with an air gap on the image side;
A zoom lens consisting of a rear group having one negative lens and two positive lenses, and satisfying the following conditions |R_1_-_2/R_1_-_1|≦1 (However, R_
1_-_2<0) However, R_1_-_1: Radius of curvature of the object side of the positive lens of the front group of the fifth lens group R_1_-_2: Radius of curvature of the image side of the positive lens of the front group of the fifth lens group