JPS6224210A - Variable power optical system - Google Patents

Abstract

PURPOSE:To obtain a high variable power ratio by a small moving extent, by varying a refractive power of a lens group of a part of plural movable lens groups, and moving it on an optical axis. CONSTITUTION:By moving linearly the first and the second lens groups on an optical axis as indicated with an arrow and also varying a refractive power of the first lens group I, variable power is executed by maintaining an image surface at a prescribed position. In this way, by varying the refractive power of the first lens group I and moving it, a prescribed variable power ratio is obtained by a small moving extent as a whole, and the overall length of the lens is shortened and a high variable power is obtained. Also, by adopting a constitution for moving linearly both groups of the first and the second lens groups on the optical axis, the structure of a lens barrel can be simplified.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a variable magnification optical system, and in particular to a variable magnification optical system that reduces the amount of movement of a lens group and shortens the overall length of the lens while increasing the variable magnification. This invention relates to a variable magnification optical system that is simplified.

(Prior art) In a conventional variable magnification optical system, at least two lens groups, a lens group for variable magnification and a lens group for correcting image plane fluctuations accompanying variable magnification, are arranged so that these lens groups are mutually located on the optical axis. The magnification was changed by moving it so as not to interfere with it. Among these, the lens group for correcting image plane fluctuations is required to be moved non-linearly on the optical axis with high precision. Generally, in order to move the lens group non-linearly on the optical axis with high precision, the cam mechanism on the lens barrel must be constructed with high precision, which tends to make the lens barrel structure complicated. .

'Furthermore, in order to obtain a high variable power ratio in a variable power optical system, it is necessary to strengthen the refractive power or increase the amount of movement of the variable power lens group. However, if the refractive power of the lens group is strengthened, aberration fluctuations due to zooming will increase, and it becomes difficult to satisfactorily correct these aberration fluctuations, especially in the case of a fast lens type. Furthermore, increasing the amount of movement of the lens group increases the overall length of the lens, making it difficult to reduce the size of the entire lens shape.

On the other hand, a lens system that changes the refractive power of at least one lens group in the lens system and moves at least one lens group on the optical axis to correct the magnification change and the image plane fluctuation that accompanies the magnification change. For example, the double optical system is JP-A-59-1
01618, JP-A-59-116710, JP-A-59-
No. 116711 and Japanese Patent Application Laid-Open No. 118712/1983. However, since these variable power optical systems generally have a fixed lens group, it is difficult to achieve high variable power while reducing the amount of movement of the lens group and to downsize the entire lens system. .

(Problems to be Solved by the Invention) An object of the present invention is to provide a variable power optical system that achieves high variable power while reducing the amount of movement of the lens group as a whole, and further reduces the size of the entire lens system. shall be. A further object of the present invention is to provide a variable magnification optical system in which the lens barrel is simplified by moving the lens group linearly on the optical axis without any complicated movement. .

(Means for solving the problem) By moving a plurality of lens groups on the optical axis and changing the refractive power of only some of the plurality of lens groups, the magnification of the entire system can be changed. This corrects the accompanying image plane fluctuations.

The features of this shrub invention are described in the Examples.

(Example) FIG. 1 is a schematic diagram of an optical system according to Example 1 of the present invention. The figure (A) shows the optical arrangement at the wide-angle end, and the figure (B) shows the optical arrangement at the telephoto end. Further, in the same figure, reference numerals 1 and 2 denote the first lens group and the second lens group which constitute each variable magnification optical system. In this embodiment, the first and second lens groups are moved linearly on the optical axis as shown by the arrows, and the refractive power of the first lens group I is changed to change the magnification while maintaining the image plane at a constant position. There is.

In this embodiment, by moving the IF lens group I while changing its refractive power, a predetermined variable power ratio can be obtained with a small amount of overall movement, and the overall length of the lens can be shortened and the variable power can be increased. A variable magnification optical system has been achieved. And furthermore, the first
By adopting a configuration in which both groups of the second lens group are moved linearly on the optical axis, a variable power optical system with a simplified lens barrel structure is achieved.

Next, the paraxial refractive power arrangement of the variable magnification optical system shown in FIG. 1 will be explained.

1. The refractive power of the 72nd lens group, ■ is φ1゜φ2, respectively.
Let el be the distance between the principal points of both lens groups. As the entire system zooms, the refractive power φ1 of the lens group. by changing the refractive power φ2. of the second lens group. is constant.

In order to change the magnification of all prefectures and to correct the image plane fluctuation accompanying the magnification change, the refractive power of the lens group φ1. is the refractive power of the entire system, Φ, and the second
If the distance from the lens group to the image plane is SK, then φ, = φ(1-5K·φ2,). The principal point spacing e at this time is Q, = (φW+φ1−φ)φClear°φ2.

For now, let's assume that the refractive power arrangement at the wide-angle end is φ, −-1770φ
2 = 1/40. e H=50, 1st", 2nd
Table 1 shows the numerical values obtained when each lens group is moved linearly on the optical axis and the refractive power φ of the lens group is changed.

In addition, in Table-1, t3. t2 is the amount of movement on the optical axis with reference to the positions of the first and second lens groups at the wide-angle end.

Table-1 F is the focal length.

As shown in Table 1, by changing the refractive power φ and linearly moving the first lens group from 0 to 20 mm and the second lens group from 0 to -20 nm on the optical axis, the entire system It is possible to realize a variable magnification optical system that continuously changes the focal length from 35 mm to 70 mm.

On the other hand, in Example 1, if the lateral magnification of the second lens group is β, the distance between object and image points is D, and the distance lawn between the lens group and the image plane is D', then D=A β+-+ C β D'=Aβ It can be expressed as ten. At this time, the refractive power change Δφ1 of the first lens group due to the magnification change of the entire system can be expressed as ΔφI=DD'. Here, A, B, C, A', and C' are each constants.

As is clear from the above relational expression, if D is changed depending on the value of β, Δ
It is possible to reduce φ to some extent. In other words, if the method of movement of the first lens group is appropriately selected, it is better to change the refractive power while moving it on the optical axis as in this example than to change the refractive power while keeping it fixed. It becomes possible to reduce the amount of change.

FIG. 2 is a schematic diagram of an optical system according to a second embodiment of the present invention. The figure (A) shows the optical arrangement at the wide-angle end, and the figure (B) shows the optical arrangement at the telephoto end. In the same figure, I, ■, and ■ are the first, second, and third lens groups, respectively, constituting the variable power optical system.

In this embodiment, the first, second, and third lens groups are moved linearly on the optical axis as shown by the arrows, and the refractive powers of the first lens group and the third lens group (2) are changed to maintain a constant position on the image plane. The magnification is changed while maintaining the same value.

In this embodiment, by moving the first and third lens groups while changing their refractive powers, a predetermined zoom ratio can be achieved with a small amount of overall movement, resulting in a shortened overall lens length and a high zoom ratio. A variable magnification optical system has been achieved. And then the first one. By adopting a configuration in which the second and third lens groups are moved linearly on the optical axis, a variable magnification optical system with an m-cylindrical lens structure and a tm element is achieved.

The refractive powers of the first, second, and third lens groups are each φ.

φ2, φ3, the distance between the principal points of the 2nd lens group and the 2nd lens group, and the distance between the principal points of the 2nd lens group and the 3rd lens group is e l + 82, respectively.
shall be. At this time, φ, = -1/30° φ2 = I/45
, φs = 1 / 45.71, e I = 30
, e2=20, and the calculated values when φ1 and φ3 were changed are shown in Table 2. However, 1. ．． 12, t3
is the amount of movement on the optical axis when the position of each lens group at the wide-angle end is taken as a reference.

Table-2 As shown in Table 2, φ1 and φ3 are changed, and the 1st lens group is changed from 0 to 10mm, and the i2 lens group is changed from 0 to 110mm.
mm, and by moving the third lens group linearly on the optical axis from 0 to 10++ui, a variable magnification optical system is realized in which the focal length of the entire system changes continuously from 20IIIm to 60mm.

In this embodiment, the refractive power of the lens group may be changed by, for example, using a liquid lens and changing the water pressure of the liquid to change the radius of curvature of the lens surface, or by molding a transparent elastic material such as silicone rubber into the shape of the lens. The radius of curvature of the lens surface may be changed by applying pressure to the outer edge.

(Effects of the Invention) According to the present invention, by changing the refractive power of some of the plurality of movable lens groups and moving them along the optical axis, movement is reduced compared to conventional variable magnification optical systems. It is possible to achieve a compact variable power optical system that can obtain a high variable power ratio with a small amount of power. Furthermore, by linearly moving each lens group to change the magnification, a variable magnification optical system with a simple lens barrel structure can be achieved. Furthermore, if the method of moving the lens group is appropriately selected, the amount of change in the refractive power of the lens group can be reduced.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of an optical system according to an embodiment of the present invention, in which (A) is the wide-angle end and (B) is the telephoto end. In the figure, I, ■, ■ indicate the first, second, and third lens groups, respectively, and arrows indicate the movement direction of the lens groups during zooming.

Claims (1)

[Claims] It is characterized by moving a plurality of lens groups on the optical axis and changing the refractive power of only some of the plurality of lens groups, thereby correcting the magnification change of the entire system and the image plane fluctuation accompanying the magnification change. Variable magnification optical system.