JPH03251810A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain the compact zoom lens of simple constitution which hardly has focus position error variation pertaining to power variation by moving a 3rd and a 5th lens element associatively and correcting the shift in the focus position due to the power variation. CONSTITUTION:The zoom lens consists of a 1st lens element which has positive refracting power and is fixed in power variation, a 2nd lens element which has negative refracting power and moves forth and back for the power variation, the 3rd lens element which has negative refracting power, a 4th fixed lens element which has positive refracting power, and the 5th lens element which has positive refracting power in order from the object side, and the 3rd lens element is associated with part or the whole of the 5th lens element to correct the shift in the focus position due to the power variation. Further, focusing is performed by the 3rd lens element and the correcting part group of the 5th lens component which are associated, so movable elements becomes smaller in number, the mechanism of the lens frame is simplified, and the movement quantity is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens, and particularly to a zoom lens suitable for use in video cameras and the like with a high zoom ratio and little focusing error.

(Prior Art) Conventionally, zoom lenses used in video cameras, etc. are composed of four lens components having positive, negative, negative, and positive refractive powers in order from the object side, and the first lens component has a refractive power that can be used even when changing the magnification. It remains fixed, and the magnification is changed by moving the second lens component, and the change in the position of the image plane due to magnification is corrected by moving the third lens component, and it remains fixed even when changing the magnification. A zoom lens that forms an image on an image plane using a certain fourth lens component is well known. However, it is for /IX type video camera and has an aperture of F1.
Most zoom lenses have a zoom ratio of around 4x and a magnification ratio of up to 8x.
If the third lens component, which is a correction lens component, has a negative lens element or a simple configuration similar to that, and you want to sufficiently suppress aberration fluctuations that occur with zooming, especially spherical aberrations and axial chromatic aberrations, it is necessary to There was a drawback that the system tended to become large.

In addition, focusing is often performed by moving the first lens component or the fourth lens component, but in each case, there are three movable lens components that have independent or different movement paths, resulting in a complicated lens frame structure. Ta.

On the other hand, JP-A-62-24213 and JP-A-63-1
As seen in Publication No. 23009, it is composed of four lens components each having positive, negative, positive, and positive refractive powers in order from the object side, and the first lens component and the third lens component are fixed during zooming, It is known that the second lens component is moved in one direction to perform magnification change, and the fourth lens component is moved back and forth to compensate for fluctuations in the focal position caused by the magnification change. In this type of zoom lens, the third lens component does not move when changing the magnification, so the distance between the first lens component and the aperture can be shortened, and the diameter of the front lens can be made smaller than in the above-mentioned type of zoom lens. I can do it. However, when trying to achieve a high zoom ratio of about 6x, the amount of movement of the fourth lens component to correct the image plane position due to zooming becomes large, and the fourth lens component responds to the slight movement of the second lens component. The rate of change in movement of the component is particularly steep from the intermediate focal length to the telephoto end, and when moving the fourth lens component with a zoom cam, it is easy for the focus to shift during zooming due to manufacturing errors, etc., and when using a stepping motor, etc. teeth,
This has the disadvantage that the focus position error is likely to fluctuate due to zooming, such as poor followability due to zooming.

(Object of the Invention) The object of the present invention is to provide a compact zoom lens that is suitable for video cameras, etc., has a high zoom ratio of about 6x or more, has a simple configuration, and is less likely to cause focal position error fluctuations due to zooming. Our goal is to provide lenses.

(Means for solving the problem) Basically, the zoom lens of the present invention has a first lens having a positive refractive power that remains fixed during zooming, starting from the object side.
a lens component, a second lens component that has negative refractive power and moves back and forth to change magnification, a third lens component that has negative refractive power, a fixed fourth lens component that has positive refractive power, and positive refraction. The third lens component is composed of a fifth lens component having a force, and the third lens component and a part or all of the fifth lens component are moved in conjunction with each other, thereby correcting the movement of the focal position due to zooming.

In the present invention, it is further preferable to perform focusing by moving part or all of the third lens component and the fifth lens component in conjunction with each other.

The zooming is performed by moving the second lens component from the wide-angle side to the telephoto side, from the object side to the image side.

The present invention is applicable not only when the entire fifth lens component has the role of a compensator in conjunction with the third lens component, but also when a part of the fifth lens component changes in conjunction with the third lens component. This also includes the case of correcting changes in the image plane position due to magnification. In the following, the subgroup of the fifth lens component that moves as the magnification changes is referred to as a correction subgroup. Therefore, when the entire fifth lens component moves with zooming, the correction partial group matches the fifth lens component.

Specifically, in the zoom lens of the present invention, the first lens component includes at least one positive lens and at least one negative lens, and the second lens component includes at least two negative lenses and at least one negative lens. The third lens component consists of at least one negative lens, the fourth lens component consists of at least one positive lens, and the correction partial group in the fifth lens component consists of at least one positive lens. It is desirable that the lens includes a lens and at least one negative lens, and satisfies the following conditions.

0.25<lf, +Fw/(fwZ)<0.4
(1) 2.0<fs/fw<3.0
(2) However, f is the composite focal length of the second lens component, f
5 is the composite focal length of the correction subgroup of the fifth lens component, f8
is the focal length of the entire system at the wide-angle end, Fw is the F number at the wide-angle end, and Z is the zoom ratio.

More specifically, in the zoom lens of the present invention, the first lens component includes, in order from the object side, a positive doublet consisting of a negative meniscus lens and a biconvex lens, and a positive meniscus lens with a convex surface facing the object side. The second lens component consists of, in order from the object side, a negative lens with a strongly concave surface facing the image side, and a negative doublet consisting of a biconcave lens and a positive lens, and the third lens component consists of one lens. It is desirable that the lens be made of a negative lens and satisfy the following conditions.

nz-> 1.6 v2- ν2+ 20 (3) (4) however, 2- 'v　2+ : Average value of the refractive index of the negative lens in the second lens component : Atsube number of the positive lens in the second lens component : Average value of the Atsube number of the negative lens in the second lens component It is.

(Function) In the basic configuration of the zoom lens of the present invention, the fact that the third lens component moves 1:1 in conjunction with the correction portion group of the fifth lens component as the zoom lens changes is a simple configuration with high performance. This is an extremely advantageous condition in the following points when designing a variable power zoom lens. In other words, part of the function of correcting the movement of the image plane during zooming as a compensator can be assigned to the third lens component, and the function of correcting the movement of the image plane during zooming can be shared by the third lens component. The amount of movement can be reduced. As a result, it is possible to alleviate deviations in the focal position due to manufacturing errors or clearances of the zoom cam or the like regarding the correction partial group.

Furthermore, if focusing is performed by the correction subgroups of the third lens component and the fifth lens component that work together as described above, the movable component will be reduced compared to when focusing is performed by other lens components. In addition, the mechanism of the lens frame is simplified, and the amount of movement for focusing is reduced compared to the case where the third lens component and the fifth lens component are moved independently. Furthermore, the effective diameter of the front lens can also be made smaller than when the first lens component is moved.

At least one negative lens is provided in each of the first lens component having positive refractive power and the correction partial group that moves with zooming in the fifth lens component, and at least one negative lens is provided in the second lens component having negative refractive power. The positive lens is included in order to sufficiently correct axial chromatic aberration and lateral chromatic aberration in the entire range of magnification.

The reason why the second lens component includes at least two negative lenses is to ensure that the second lens component has sufficient refractive power, to reduce the amount of movement required for zooming, and to make the diameter of the front lens compact. It's for a reason.

Condition (1) concerns the appropriate value of the focal length of the second lens component; if the absolute value of the focal length exceeds the upper limit and becomes large, it is advantageous in terms of aberration correction, but the length from the first lens component to the third lens component As a result, a compact lens system cannot be obtained. If the lower limit is exceeded, with the above-mentioned simple lens configuration, it becomes impossible to correct aberration fluctuations due to zooming, especially fluctuations in distortion and coma aberration, and negative distortion at the wide-angle end becomes excessive.

Condition (2) concerns the focal length of the correction subgroup in the fifth lens component; if the lower limit is exceeded, the length from the front of the fifth lens component to the imaging surface tends to become shorter, which is advantageous for shortening the overall length. However, the angle of view of the entire fifth lens component becomes larger, and the height at which the light flux incident on the corner of the screen passes through the first lens component becomes higher, leading to an increase in the front lens system. When the focal length becomes longer than the upper limit, not only does the total length of the lens system become longer, but also the diameter of the lens in the fifth lens component becomes larger in order to obtain a predetermined aperture.

In the specific configuration of the zoom lens of the present invention, the first lens component includes, in order from the object side, a positive doublet consisting of a negative meniscus lens and a biconvex lens, and a positive meniscus lens with a convex surface facing the object side. The reason for this configuration is mainly to suppress fluctuations in spherical aberration and coma aberration from the intermediate focal length to the telephoto end. The positive meniscus lens on the image side is configured almost abranatically with respect to the axial light beam, and also has the effect of correcting negative distortion generated in the second lens component having strong negative refractive power.

The second lens component consists of, in order from the object side, a negative lens with a strongly concave surface facing the image side, and a negative doublet consisting of a biconcave lens and a positive lens. While suppressing the increase in size of the entire system due to the increased thickness and thickness, it is possible to reduce fluctuations in aberrations, especially fluctuations in distortion and astigmatism, due to zooming.

The zoom lens of the present invention has a structure in which the third lens component has only one negative lens, since the absolute value of the amount of movement of the third lens component during zooming is generally smaller than that in a normal four-component zoom lens. However, the contribution to fluctuations in aberrations such as chromatic aberration and spherical aberration can be reduced.

Condition (3) relates to the refractive index of the negative lens constituting the second lens component, and if this condition is violated, it becomes difficult to correct negative distortion at the wide-angle end depending on the above-described configuration.

Condition (4) relates to the difference in Abbe number between the negative lens and the positive lens that make up the second lens component; if the condition is violated, the fluctuation of chromatic aberration during zooming, especially the fluctuation of chromatic aberration of magnification, becomes large, and the image becomes distorted at the wide-angle end. On the telephoto side, the short-wavelength imaging point tends to shift too much in the direction of large image height, and in the direction of small image height on the telephoto side.

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

In the second embodiment, one positive and negative plastic lens is used in each of the correction subgroups in the fifth lens component,
These lenses are marked with a wooden stamp. Plastic lenses generally have a change in refractive index due to changes in environmental temperature, but in the embodiments of the present invention, by optimally combining the refractive powers of each plastic lens, changes in focal position due to changes in refractive index can be avoided. is suppressed. These plastic lens materials include PC (polycarbonate) PM
MA (polymethyl methacrylate) or the like is used.

The refractive power of these materials changes linearly with temperature. The data is shown below.

PCPMMA Standard refractive index (20°C) 1.583 1.492
Refractive index (50℃) 1.5788 1.413
The constants of the aspherical coefficients in the 84th embodiment are as follows.

First example f=1. oo ~ 5.80 2ω = 45.48° ~ 7.64° D F: 2.0 ~ 2.7 f B: 0,772 However, X: The vertex of the aspherical surface is the origin, and the object is Coordinate h going from the side to the image side: Coordinate C perpendicular to the optical axis with the apex of the aspherical surface as the origin: Represents the paraxial curvature of the aspherical surface.

In addition, each symbol in the table is as follows: R is the radius of curvature of each refractive surface, D is the distance between the refractive surfaces, N is the refractive index of the lens material, C is the Abbe number, f is the focal length of the entire lens system, and 2ω is the image angle, F is the F number, and fB is the back focus.

Variable interval 5.80 1.6883 f = 3.295 f4 = 2.035 0.1883 0.1096 f, = -0,836 f, = f, = 2.717 0.3951 0.2251 f, = -3,173 Second example f=1. oO~5.69 2ω=47.9°~8.3@1] 5.958 0.14 F: 1.4~1.8 fB=0.25 1.80518 25.4 20th surface Aspheric coefficient K = -1,45763X10-" A4 = 1.28500X10' AG = -4,20649xlO' A, = 2.27094X10" Variable interval 5.69 2.4272 0.3297 0.0725
1.0333 0.8267f f = 4.845 f4 = 2.732 (Effect of the invention) As seen in each example and the aberration diagram, the zoom lens of the present invention has a high zoom ratio of about 6 times or more. However, it has a simple configuration, and aberrations are well corrected over the entire magnification range. It is a suitable zoom lens.

[Brief explanation of drawings]

FIG. 1 is an optical layout diagram showing the basic configuration of the zoom lens of the present invention, FIGS. 2 and 3 are sectional views of the first and second embodiments of the zoom lens of the present invention, and FIG. 4 , and FIG. 5 are aberration curve diagrams of the first embodiment and the second embodiment, respectively. Ganjin Patent Hatake Konica Co., Ltd. Agent Ro Ganjin Patent attorney Fumio Saina (2 others) Fig. 7 ω=38°ω=38 Spherical aberration, astigmatism, and distortion chart (a) 00 F 1.4 ω:239 ω=239 Spherical aberration, astigmatism, and distortion chart (a) 00 F 2.0 ω= 227° ω = 221 Spherical aberration, real point aberration, and distortion diagram (b) 42 F 2.0 ω = 99 ω = 99° Spherical aberration, astigmatism, and distortion diagram (b) 14 Spherical aberration 41st aberration Z diagram (c) 1-curve aberration 69 Spherical aberration Non-linear aberration Surrounding aberration procedure correction document (self-proposed) April 11, 1990

Claims (2)

[Claims] (1) In order from the object side, the first lens component has a positive refractive power and is fixed depending on the magnification change, the second lens component has a negative refractive power and moves back and forth to change the magnification, and the negative refractive power a fixed fourth lens component having a positive refractive power, and a fifth lens component having a positive refractive power, the third lens component and a part or all of the fifth lens component are interlocked with each other. 1. A zoom lens that corrects movement of a focal point position due to zooming by moving the focal point while changing the magnification. (2) In the zoom lens according to claim (1), the third
A zoom lens characterized in that focusing is performed by moving a lens component and part or all of a fifth lens component in conjunction with each other.