JPS6180213A - variable magnification optical system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a variable power optical system using a variable refractive power element.

[Prior art]

Conventionally, in variable power optical systems, in order to perform variable power while maintaining the image plane of the entire system at a constant position, it has been necessary to move at least two lens groups in a predetermined relationship during variable power. In this way, in order to move two or more lens groups so that they do not collide during zooming, it is necessary to maintain a constant distance or more at all times, which is a constraint on making the lens system compact. Furthermore, at least one of the lens groups to be moved during zooming requires a mechanism to move non-linearly, and such non-linear movement makes it difficult to move the lens group smoothly. Furthermore, an expensive moving mechanism was required.

As a solution to these points, Japanese Unexamined Patent Publication No. 59-116
There is a publication No. 711. This lens includes a lens group A that changes the magnification of the entire system by moving on the optical axis, and a lens group B that includes at least one variable refractive power element, and the refractive power of the variable refractive power element is changed. A variable magnification optical system is disclosed that maintains the image plane of the entire system at a constant position.

In such a variable power optical system, it is desired to reduce the refractive power difference Δn of the variable refractive power element and to make it easier to constrain or drive the variable refractive power element. In the optical system, the refractive power of the lens group B at the wide-angle end is ψW,
When the refractive power at the telephoto end is ψT, and the refractive power in one zooming state during that time is ψM, the following conditional expression is presented.

[Summary of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a variable magnification optical system using a variable refractive power element, in which a large change in focal length can be obtained even with a small difference in refractive power between the variable refractive power elements. be.

The present invention provides a variable magnification optical system that includes a lens group A for changing the magnification of the entire system and at least one variable refractive power element, and forms an image of the entire system by changing the refractive power of the element. It has a lens group B that keeps the position of the surface constant, and the lens group B
The objective is to achieve the above object by configuring an optical system so that the object distance is infinite or has a very large value in a variable power state including a variable power range.

The present invention will be explained in detail below.

[Example] Figures 'i1 (A''), (B), and (C) are schematic diagrams showing an example of a variable magnification optical system for explaining the basic configuration of the variable magnification optical system according to the present invention. is the wide-angle side, (B) is the intermediate state, (C
) is a sectional view of the lens on the telephoto side. In Figure 1,
The variable magnification optical system consists of, in order from the object side, lens group A and lens group B with positive refractive power, and lens group A further includes lens group A1 with positive refractive power arranged on the object side and lens group A1 with positive refractive power arranged on the image plane side. It consists of a lens group A2 having negative refractive power arranged at . The lens group A2 is movable in the optical axis direction, and the movement of the lens group A2 changes the magnification of the entire system. Lens group B is spatially fixed and has at least one variable refractive power element, which changes the refractive power of lens group B to adjust the refractive power of the entire system in each state during zooming. It has the function of keeping the image plane I at a constant position.

Here, the object distance to lens group B in a certain zooming state, that is, the image formation position by lens group A and the distance between the front principal point of lens group B is g, the refractive power of lens group B is ψ, and the distance between the image formation position by lens group A and the front principal point of lens group B is Let g' be the distance between the rear principal point and the image plane 1 of all prefectures. g, ψ.

The following well-known relationship holds between g′. Especially g, ψ at the wide-angle end
, g' is gw, ψw, g'w, and similarly, the value at the telephoto end is g
It is expressed as T, ψT, and g'7.

For simplicity, it is assumed that lens group B is a thin lens system.

Then, in order to keep the image plane I of the entire system constant during zooming, it is necessary that g'=constant. Especially g′
w=g'T, and the refractive power difference Δψ of the lens group B between the wide-angle end and the telephoto end is expressed as Δψ=ψT−ψW W gT =11 ny ~--(1) g W g T . In other words, in order to maintain the image forming surface of the entire system at a constant position regardless of the magnification change state, it is necessary to change the refractive power of the variable refractive power element belonging to lens group B by at least 1Δψ1, and as described above, this It is desirable to make 1Δψ1 as small as possible.

In the above-mentioned Japanese Unexamined Patent Publication No. 59-116711, the refractive power ψ of the lens group B takes an extreme value during zooming, thereby reducing 1ΔψI. In this case, this condition can be rephrased as configuring the lens group A so that the object distance g to the lens group B takes an extreme value during zooming, and setting gT:gw to reduce 1Δψ1.

In contrast, in the present invention, in order to reduce 1Δψ1, the lens group A is configured to reduce II/g l and 11/g 71. That is, as is clear from equation (1), even if I g W 7g Tl is large, Ig
If wl and IgTI are sufficiently large, 1Δψ1 is small. Therefore, in the present invention, lens group A is configured such that an object relative to lens group B is at an infinite distance or sufficiently far away in a certain zoom state. In other words, when the absolute value of the object pressure Kg for lens group B becomes infinite or sufficiently large in the variable power state, I
The value of gl can be increased, and 1Δψ1 can be decreased. As shown in FIG. 1(B), in the intermediate state, the object point of lens B is formed at a position substantially at infinity. In this way, by setting the object distance to lens B to infinity or sufficiently large within the variable power range, 1Δp
1 can be made smaller.

Table 1 shows numerical values of a specific example of the variable magnification optical system shown in FIGS. 1(A), 1(B), and 1C.

Table 1! #A, = 0.006667 ψA2 = -0,009
091e1+e2=80 g'=40 In addition, ψAl is the focal length of lens group A1, ψA2 is the focal length of lens group A2, and el is lens group A1 and lens group A2.
e2 is the principal point distance between lens group A2 and lens group B, g is the object distance to lens group B, g
' is the distance between lens group B and the imaging plane of the entire system, ψ is the refractive power of lens group B, and F is the focal length of the entire system. Table 1 shows the values at each zoom position when the object distance for the entire system is infinite and lens group A2 is moved toward the image plane on the optical axis when zooming from the wide-angle side to the telephoto side. ing. In (A) corresponding to the numerical example in Table 1, the focal pressure #F of the entire system is
A graph of the refractive power ψ of lens group B is shown in FIG. 2(B). In this example, it can be seen that when el=e2=40, the object distance g to the L/7 lens group B becomes infinite.

Further, the variable magnification optical system of the present invention is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 59-116.
If the technique disclosed in Japanese Patent No. 711 is used in combination, the effect will be even greater. That is, as shown in Japanese Patent Application Laid-Open No. 59-116711, there is a variable power state in which the refractive power of lens group B takes an extreme value, and a variable power state in which the object distance g to lens group B is infinite as in the present invention. By continuously changing the magnification between the two states, a large magnification ratio can be obtained with a small change in the refractive power of the lens group B.

Table 2 shows numerical examples in this case.

Table 2 SOA1=O,0125'fiA2=-0.02857
el+e2=50 g'=50 The lens data shown in Table 2 shows the relationship when the object distance to the entire lens system is infinite, as in Table 1, as shown in Figure 3 (A).
FIG. 3B shows the relationship between the focal length F of the entire system and the refractive power ψ of the lens group B. Comparing the graphs in Figure 2 (B) and Figure 3 (B), it can be seen that, for example, the focal length #F of the entire system is 30 ~
In numerical example 1 shown in FIG. 2(B), the refractive index difference Δn of lens group B is approximately O, OO7.
It can be seen that in numerical example 2 shown in FIG. 3(B), Δn is approximately 0 and only OO4 is required. From this, it can be seen that when zooming includes a zooming state in which the refractive power of lens group B takes an extreme value and a zooming state in which the object distance g of lens group B becomes infinite, a small refractive power difference △n results in It is possible to greatly change the focal length.

In the above example, the magnification of the entire system is changed by moving lens group A in the optical axis direction, but lens group A also has a variable refractive power element, and the refractive power of the variable refractive power element The magnification of the entire system may be changed by changing the force.

Furthermore, as a focusing method of the variable magnification optical system in the present invention, the conventional method of moving the lens in the optical axis direction may be used, but due to the change in the refractive power of lens group B, the object distance It is also possible to simultaneously eliminate movement of the imaging plane depending on the state.

As mentioned above, the variable magnification optical system of the present invention has been explained using the optical system shown in FIG. 1, but in the lens configuration shown in FIG. If a lens group is further arranged between the lens group B and the lens group B, the above description is not changed in any way by considering the lens group including that lens group as the lens group A. In addition, if a lens group is further arranged on the image plane side of lens group B including a variable refractive power element, consider lens group B including that lens group, or modify the imaging surface of lens group B. , is regarded as the object plane of the lens group disposed on the image plane side of lens group B, and the above description is not changed in any way.

Next, FIG. 4 shows an embodiment showing the specific operation of the variable magnification optical system of the present invention. Various elements whose refractive power can be varied by an external signal have been known in the past, and it goes without saying that these elements can be applied to the variable magnification optical system of the present invention. Patent application regarding person 1982-
An example using the variable refractive power element shown in No. 193868 will be explained. In Figure 4, l is the patent application filed in 1983.
It is a variable refractive power element shown in No.-193868, and 2
3 is a cylindrical container, 3 is an aperture plate made of a ferromagnetic material having a circular opening, 4 is a transparent elastic body made of gel-like silicone rubber, etc., 5 is the surface of the elastic body 4 inside the aperture of the aperture plate 2, and 6 is an electromagnet. The aperture plate 3 is movable in the axial direction within the container 2, and pressurizes and deforms the elastic body 4 by the attractive force of the electromagnet 6. Along with this, the surface 5 of the elastic body is deformed into a lens shape, and its refractive power is Change. In this way, the variable refractive power element l basically consists of a member having an elastic body and an aperture that can deform the optical surface by protruding or sinking the elastic body, and can change a large amount of refractive power with a small force. can get. or,
The refractive power element is patent application No. 58-22869 filed by the applicant.
No. 2, the method shown in Japanese Patent Application No. 59-12489, etc.
It is possible to control the shape of the lens surface to be spherical or a desired spherical shape. In addition, as a variable refractive power element, 4. Also, as shown in Japanese Patent Application No. 59-45, an element that changes the refractive index distribution in the lens medium can be used.

The lens group A shown in FIG. 4 is composed of a fixed lens group A1 and a lens group A2 movable in the optical axis direction, similar to the lens configuration shown in FIGS. 1(A), (B), and (C). By moving the lens group A2 using a helicoid or a near motor, the magnification of the entire system is changed. Lens group B in FIG. 1 here consists of variable refractive power element 1. Lens group B in FIG. 7 is lens group A consisting of potentiometers, linear encoders, etc.
The detected position of the lens group A2, that is, the variable magnification state of the entire system, is stored in, for example, a non-volatile memory (ROM).
)8. 9 increases or decreases the current flowing through the electromagnet 6,
This is a drive circuit for an electromagnet 6 that controls the refractive power of the elastic body surface 5. The non-volatile memory 8 outputs a signal to the electromagnet drive circuit in accordance with pre-stored information so that the image plane of the entire system is at a predetermined position, and the position of the image plane of the entire system is always kept constant regardless of the magnification change state.

In the two series of examples, a case was described in which the variable refractive power element was controlled by the contents stored in the nonvolatile memory, but a method using so-called TTL automatic focusing is also effective. In that case, a defocus signal is obtained using the method disclosed in Japanese Patent Laid-Open No. 54-155832, etc., and the image plane of the entire system is always at a predetermined position regardless of the object distance and magnification change state. The variable refractive power element l is driven and controlled so that the refractive power is maintained.

As described above, in the variable power optical system using the variable refractive power element according to the present invention, a large change in focal length can be obtained for a small change in refractive power of the variable refractive power element, and the control of the variable refractive power element is also easy. and allows highly accurate focal length control. Further, according to the present invention, a variable magnification optical system can be achieved by moving only one lens group or without moving any lens group,
A compact γ1 optical system with a simple lens barrel structure can be obtained.

[Brief explanation of drawings]

Figures 1 (A), (B), and (C) are diagrams for explaining the principle of the variable magnification optical system according to the present invention, Figures 2 (A), (B), and Figure 3 (A) , (B) are diagrams showing the optical characteristics of each embodiment of the variable magnification optical system according to the present invention, and FIG. (A diagram showing an example of a basic operation. A, B, Al, A, 2---- Lens group, ■--- Image plane, 1-111 Variable refractive power element, 2-1 11 cylindrical container, 3-111 opening plate, 4-111 transparent elastic body, 5-111 elastic body surface, 6---- electromagnet,
7----position detection means, 8-111 nonvolatile memory-1 9-111 electromagnet drive circuit,

Claims (1)

[Claims] (1) A lens that includes a lens group A that changes the magnification of the entire system and at least one variable refractive power element, and maintains the imaging plane of the entire system at a constant position by changing the refractive power of the variable refractive power element. A variable power optical system having a lens group B and performing variable power including a variable power state in which an object position relative to the lens group B is at infinity.