JPS59101618A - Variable power optical system - Google Patents

Abstract

PURPOSE:To form a variable power optical system having a compact and simple lens barrel structure by providing at least two lens groups, and varying the refractive powers of these two lens groups. CONSTITUTION:A variable power optical system is constituted of four lens groups, and an afocal system is constituted from the first lens group to the third lens group in order from an object side. The reflective powers of respective lens groups in a reference state are denoted as psi1, psi2, psi3 and psi4, respectively from the object side, and principal point intervals between each lens group are denoted as e1, e2 and e3, respectively. In this state, for instance, when the refractive power of the second lens group is varied to psis from psi2, if the refractive power psit of the third lens group is derived so that a focus surface of the variable power optical system becomes constant, psit=-A/(H-e2.A). Wherein H=1-e1.psi1 and A=psi1+H.psis, and accordingly, it is satisfactory that the refractive power psit of the third lens group is varied as said equation. According to this invention, the variable power optical system can be realized without moving the lens group on the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable power optical system, and more particularly to a variable power optical system that changes the focal length of the entire system by changing the refractive power of at least two lens groups.

In conventional zooming optical systems, at least two lens groups are moved on the optical axis in order to maintain the focal plane at a constant position during zooming and zooming. During zooming, the distance between these two lens groups had to be maintained to prevent them from colliding. Therefore, restrictions naturally arise in making the lens system continuous, and at least one lens group must be moved non-linearly to achieve the above objective. This made it difficult to move the lens group smoothly.

In order to realize a compact variable magnification optical system with high magnification, there is a method of moving three or four lens groups independently on the optical axis. In order to hold the lens group and realize smooth movement of the lens group, the lens barrel structure has tended to become extremely complicated.

The present invention is a variable magnification optical system that realizes a variable magnification system without moving the lens groups on the optical axis or by slightly moving some of the lens groups, and has a compact and simple lens barrel structure. The purpose is to provide a system.

A variable power optical system for achieving the object of the present invention is characterized by having at least two lens groups, and by changing the refractive power of the two lens groups, the focal length of the entire system is changed.

Next, a method of varying the magnification of the variable magnification optical system of the present invention will be explained.

For the sake of simplicity, it is assumed that a variable magnification optical system is composed of four lens groups as shown in FIG. 1, and that an afocal system is composed of lens groups from the lens group to the third lens group (from the object side). Starting from the object side, calculate the refractive power of each lens group in the standard state.

ψ2. ψ3. ψ4, and the principal point spacing between each lens group is el, e2, respectively. Let θ be. Now let's do the second one.
Ps The refractive power ψ of the sixth lens group is adjusted so that the focal plane of the time-variable magnification optical system, in which the refractive power of the lens group changes from 92 to 92, remains constant.
The result is ψ" -H-82HA.

A=91+H·ψ8 Therefore, the refractive power ψ of the third lens group may be changed as shown in the above equation.

Next, the above equation will be specifically explained using numerical values.

The refractive power arrangement of each lens group in the reference state is now ψ=:0.0
09091 θ, :9.5ψ−0.028571
e2=42-ψ, = 0.010449 63=i5ψ4= 0
．． 008774, and here the refractive power ψ2 of the second lens group is changed from the above value to o
, o o s,! Table 1 shows the refractive power ψt of the fifth lens group when it is changed by .

Table 1 Table 1. The refractive power of the second lens group is -0,02857 as follows.
By changing the refractive power of the third lens group from 0.010449 to -0,040179 at the same time as changing the refractive power from 1 to 0.005, the total focal length can be changed from 70 m to 33 m.
It is possible to realize a variable magnification optical system in which the focal plane can be changed up to 5,25911111 and the focal plane is kept constant.

In this way, in the past, the focal length of a variable power optical system was changed by moving at least two lens groups along the optical axis, but with the present invention, the focal length of the variable power optical system can be changed without moving the lens groups along the optical axis. It is possible to realize an optical system.

To change the refractive power of each lens group, for example, the lens is formed from a transparent elastic body with a hollow interior, and a liquid or gas having a refractive index different from that of air is inserted inside, and the internal state is controlled to improve the lens surface. There is a method to do this by changing the radius of curvature.

There is also a method of changing the refractive index of a glass material using the Karr effect. Also in the present invention, the refractive power is changed by changing the radius of curvature of the lens surface in the second lens group or the refractive index of the glass, and at the same time, the third lens group is
The refractive power can be controlled by changing the radius of curvature of the lens surface in the lens group or the refractive index of the glass.

In the above embodiments of the present invention, a variable magnification optical system including four lens groups has been explained as an example, but the present invention has two lens groups, and the refractive power of each lens group is appropriately changed. It can be applied to any type of variable magnification optical system that performs variable magnification. Further, in a variable power optical system having two or more lens groups, the object of the present invention can be similarly achieved by appropriately changing the refractive power of each of the two or more lens groups.

If magnification is changed by changing the refractive power of two or more lens groups, the amount of change in the refractive power of each lens group may be small, and magnification can be changed more easily.

It is preferable to change the refractive power of each lens group from negative refractive power to positive refractive power, or from positive refractive power to negative refractive power, since the magnification change effect can be efficiently achieved.

Furthermore, in the variable magnification optical system of the present invention, only the refractive power of one lens group is changed to perform a variator or compensator function, and the other lens group is moved on the optical axis to perform a variator or compensator function. You may also perform the following actions. By doing this, the degree of freedom of the variable magnification optical system increases, and a variable magnification optical system having good optical performance can be easily achieved.

As described above, according to the present invention, compared to the conventional method in which at least two lens groups had to be moved to change the magnification, it is possible to change the magnification without moving any lens groups or by moving only a part of the lens groups. A compact variable magnification optical system capable of variable magnification can be achieved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a variable magnification optical system for explaining the present invention in detail, and 1. If, nl, and IV are the first, second, third, and fourth lens groups, respectively. Applicant Canon Co., Ltd.

Claims (3)

[Claims] (1) A variable magnification optical system characterized by having at least two lens groups and changing the focal length of the entire system by changing the refractive power of the two lens groups. (2) Claim 1, characterized in that both of the two lens groups are identified when changing their refractive powers.
Variable magnification optical system as described in section. (3) At least one of the two lens groups is characterized in that the refractive power changes from negative to positive refractive power, and from positive refractive power to negative refractive power. A variable power optical system according to claim 1.