JPS62187801A - Focus method for photography system - Google Patents

Abstract

PURPOSE:To simplify the structure of a lens barrel and reduce the size of a photography system, and to easily obtain a focus on short-distance - infinite- distance bodies by varying the refracting power of a lens group so that a principal point position is constant, and focusing different bodies. CONSTITUTION:One lens group which constitutes the photography system is fixed and has at least two lens surfaces which are variable in refracting power. When the two lens surfaces of the lens group 1 are varied in refracting power while an object point P1 is image-formed on an image surface 2, the principal point position H1 is held constant and an object point P2 at different distance from the object point P1 is image-formed on the image surface 2. Consequently, while focusing is easily performed over the whole object distance range while the lens barrel structure is simplified and the photography system is made compact.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is an 1lI camera suitable for photographic cameras, video cameras, etc.
The present invention relates to a focusing method for an i-shadow system, and particularly to a focusing method for an imaging system that uses a lens group with variable refractive power in which the radius of curvature of the lens surface is changed.

(Prior Art) Conventionally, in many imaging systems, focusing from a close object to an object at infinity is achieved by moving part or all of the lens groups of the imaging system.

At this time, movement of the lens group on the optical axis is performed using a cam groove formed on the lens barrel.

For this reason, with conventional focusing methods, especially when using the rear focusing method, it is necessary to secure space in advance to move the lens group, and when floating, the lens barrel structure becomes complicated. There was a tendency to Furthermore, the center of gravity changes due to the movement of the lens group, which tends to impair the balance, especially in photographic systems with long lenses such as zoom lenses. Furthermore, in a photographing system or the like in which focusing is performed by extending the lens group, the effective diameter of the lens group increases, resulting in an increase in the size of the entire photographing system.

(Problems to be Solved by the Invention) The present invention simplifies the structure of the lens barrel and downsizes the imaging system, while making it possible to easily focus over a wide range of object distances, from objects at close range to objects at infinity. The purpose is to provide a focusing method for photography.

(Means for solving the problem) In an imaging system having at least one lens group with variable refractive power, at least one of the object-side principal point position and the image-side principal point position of the entire imaging system By changing the refractive power of the variable refractive power lens group so that the position remains constant, different objects are focused.

In particular, in the present invention, the variable refractive power lens group is fixed on the optical axis.

Also, focusing is performed by changing the refractive power of the entire system.

Other features of the invention are described in the Examples.

(Embodiment) FIGS. 1(8) and 1(II) are schematic diagrams of an optical system according to an embodiment of the present invention. In the figure, reference numeral 1 is fixed to one lens group constituting an imaging system, and has at least two lens surfaces with variable refractive power. 2 is an image plane, Pi and P2 are objects, and Hl and H2 are object-side and image-side principal points of the lens group 1, respectively.

In FIG. 1(8), an object point P1 is imaged on the image plane 2.

In Fig. 1 CB), when changing the refractive power of the two lens surfaces of lens group 1 from the state shown in Fig. 1 (Δ), the principal point position H1 is kept constant but is at a different distance from the object point P1. An object point P2 is imaged on the image plane 2.

Next, the paraxial refractive power arrangement of this embodiment will be explained.

The refractive power of the entire lens group 1 is φ1, the distance from the lens surface to the object side principal point H1 counting from the object side is Δl, the distance from the final lens surface to the image side principal point H2 is Δ°3, If S3 is the distance from the lens surface to the object, and S is the distance from the final lens surface to the image plane, then these are φ, = 'cK...
・・・・・・・・・・・・(1) Δ° = ('AK-1
) / 'CK ・・・・・・・・・・・・ (4)
It can be expressed by the following formula. Here to IA.

IBK, ICK, and 1DK are each Gaussian placket 'AK = (Φl * e l + "" + -
eK-1)'BK = ('B I + ""* -6
K-1)'CK = (ΦI + -('I *
""+ -eK-1+ ΦK)"K" (-1
31+ ""+ -8 to -1r Φe]. Here, Φi is the refractive power of each lens surface, e is the value obtained by dividing the interval between each lens surface by the refractive index of the medium between them,
It is assumed that the lens surface of the entire photographing system is composed of a cranial surface.

The object-side principal point position Hl of the imaging system composed of this surface
Alternatively, in order to perform focusing by changing the refractive power of the entire system while maintaining at least one principal point position at a constant position among the principal point positions H2 on the image plane side, the above (1,) is used during focusing.
- (2) of equation (4).

The refractive power of each lens surface may be changed so that equation (3) or equations (2) and (4) are always constant.

Next, for simplicity, the lens group 1 with variable refractive power is composed of a single convex lens, and the object distance ai s + is set by two object points, for example, S
When focusing on l;-■ and S, =-10,
The aforementioned variables are S X'=0.474.

e+=o, l, the lens group 1 is made of a transparent elastic body, for example silicone rubber (n, = 1.5), and while keeping the object side principal point position H1 constant during focusing, for example Δ1 =
0.0525, and Table 1 shows numerical examples when the overall refractive power is controlled by changing the radii of curvature rl and r2 of the two lens surfaces while keeping this value constant.

Table-1 As shown in Table 1, the radius of curvature rl of the lens surface.

While changing r2, the refractive power of the entire system was changed from 1.9 to 2.
By changing it to 0, it is possible to focus on two object distances while keeping the object side principal point position H1 at a constant position.

FIGS. 2A and 2B are schematic diagrams of an optical system according to another embodiment of the present invention. In this embodiment, the photographing system is composed of two lens groups 21 and 22, and the lens group 21 is composed of a single lens, and by changing the refractive power of both lens surfaces and changing the refractive power of the entire system. , object side principal point position H2
1 constant with respect to the image plane 23, the two object points P
Focuses on IO and P2O.

Note that the lens groups 21 and 22 are both fixed.

Now, the total refractive power of the lens group 21 is φ, the distance from the 1st lun's surface to the object is SL, the refractive power of the entire lens group 22 is φ■, and the distance from the 1st lun's surface on the object side to the object side principal point H21 Δ■1, change the distance from the final lens surface to the image plane side principal point H22 by Δ°■, and set the distance from the final lens surface to the image plane as S.
If K' is the refractive power φ■ in the lens group 22.

The distance *S K' corresponds to equations (1) and (2) in the embodiment shown in FIGS. 1(8) and (B), respectively.

Therefore, in order to focus on different objects by changing the refractive power of the lens group 21 while keeping the entire refractive power of the lens group 22 constant (2).

The refractive power of each lens surface may be determined so that the value of equation (3) is always constant.

Next, for simplicity, the lens group 21 is composed of a single convex lens made of a transparent elastic material, for example, silicone rubber (n d = 1.4059), and the radius of curvature of both lens surfaces is rl.

When focusing on two objects, for example S,=-■ and S,=-10, by changing r2 and changing the refractive power of the entire system, the aforementioned variables are changed to φn=1.9°SK'=0. 1
4677, e, = 0.1, and the distance 1ipid from the image side principal point position H12 of the lens group 21 to the lens surface of the lens group 22 is d = 0.1526 (S, =-
ω).

d = 0.0373 (S, = -10), and
For simplicity, the lens group 22 is a single lens, and the lens group 21 is
and the refractive power of the lens surface of the lens group 22 in order from the object side to Φ1. Φ2. Φ3. Table 2 shows numerical examples when Φ4 is used.

Table 2 By changing the refractive power as shown in Table 2, it is possible to focus on two different objects while keeping the object-side principal point position constant.

Also, at this time, the two lens surfaces R11 of the lens group 21,
The table below shows the changes in the radius of curvature of R12 and the various variables mentioned above.
It will be like 3.

Table 3 In the above embodiments, the object-side principal point position of the imaging system was kept constant, but the lens group was designed to maintain the image-side principal point position at a constant position instead of the object-side principal point position. The object of the present invention can also be achieved by changing the refractive power of the lens.

In the above embodiments, the lens group may be composed of a plurality of lenses, and the refractive power of at least two lens surfaces may be changed. Furthermore, the photographing system may be constructed using two or more lens groups with variable refractive power.

(Effects of the Invention) According to the present invention, it is possible to simplify the lens barrel structure and make the imaging system more compact without moving the lens group on the optical axis during focusing, and at the same time, over the entire object distance, It is possible to achieve a focusing method for a photographing system that allows easy focusing. Furthermore, by keeping the principal point position of any block constant, analysis on the paraxial arrangement becomes easier. Furthermore, by keeping the principal point position constant on the object side or image plane side, there is no need to move the lens group during focusing, so it is possible to achieve an imaging system with a simple lens barrel structure.

[Brief explanation of drawings]

Figures 1 (A) and (B) are schematic diagrams of an optical system according to one embodiment of the present invention, and Figures 2 (8) and (n) are schematic diagrams of an optical system according to another embodiment of the present invention. . In the figure, 1.21 is a lens group with variable refractive power, and 2.23 is an image plane, Pi. P2. PIO and P2O are the object, Hl and H21 are the principal point positions on the object side, and H2 and H22 are the principal point positions on the image plane side.

Claims (2)

[Claims] (1) In an imaging system having at least one lens group with variable refractive power, at least one principal point position of the object side principal point position or the image side principal point position of the entire imaging system is kept constant. A focusing method for a photographing system, characterized in that different objects are focused by changing the refractive power of the variable refractive power lens group. (2) The focusing method for a photographing system according to claim 1, wherein the lens group having variable refractive power is fixed on the optical axis.