JPS58215619A - Lens system with variable focal length - 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 The present invention relates to a lens system in which the focal length can be truncatedly variable by replacing a part of the lens system with a new lens group.

Conventionally, a method has been proposed in which an auxiliary lens is built into the camera body and the focal length of the entire lens system is changed by attaching and detaching the auxiliary lens to a part of the main lens system, for example, in Japanese Patent Laid-Open No. 56-94318. .

Lens systems in which the focal length is changed by attaching and detaching an auxiliary lens to a part of the main lens system are generally large and inconvenient to handle. The lens system proposed in the above-mentioned Japanese Patent Laid-Open No. 56-94318 also has a telephoto ratio of the main lens system exceeding 1-1.

In order to maintain good optical performance and change the focal length by inserting an auxiliary lens into the main lens system, the lens configuration inevitably becomes complex.

An object of the present invention is to obtain a lens system that is compact and has a focal length that is intermittently variable by two or more while maintaining good aberrations.

A feature of the lens configuration for achieving the object of the present invention is that in a lens system having two lens groups, a front group having a positive refractive power and a rear group having a negative refractive power, the front group is extended, and the rear group is extended. The focal length of the entire lens system is intermittently changed by replacing the group with an auxiliary lens group having a negative refractive power different from the refractive power of the rear group.

In order to make the overall length of the main lens (from the first surface of the lens to the focal plane) short and compact, this lens system of the present invention has a front group with positive refractive power and a rear group with negative refractive power. It consists of

Then, when the total length of only the main lens system is shortened and the focal length is to be changed, the focal length of the entire lens system is changed by extending the front group and replacing the rear group with the auxiliary lens group. There is. By newly setting an appropriate air gap in this way, it is possible to maintain good aberration correction even if the auxiliary lens is replaced with a sharp one.

In addition, the air gap is expanded by moving the front group toward the object side, making it mechanically easier without moving the rear group, which has some problems. This makes it easy to maintain the positional relationship between the blur mechanism and the focal plane unchanged.

In the lens system according to the present invention, it is preferable from aberration correction and mechanical standpoints to arrange an aperture mechanism or a shutter mechanism between the front group and the rear group. For this reason, the front group is extended toward the object side, and the aperture between the front and rear groups is fixed, simplifying the mechanism. Furthermore, the positional relationship between the diaphragm mechanism and the focal plane remains unchanged, making it easy to correct aberrations.

The main lens system in the variable focal length lens system according to the present invention is preferably compact and has the following lens FpX configuration in order to achieve good aberration correction.

The front group consists of, in order from the object side, a positive meniscus lens group with a convex surface facing the object side, a negative second lens group, and a positive third lens group, and the rear group has an aspherical concave surface facing the object side. The fourth lens group has a negative meniscus.

Further, it is preferable for the auxiliary lens group to be composed of at least one positive lens and at least one negative lens in order to correct aberrations, particularly chromatic aberrations.

In the present invention ζ, by storing a plurality of auxiliary lens groups in the camera and exchanging the auxiliary lens groups in a timely manner, a lens system with a desired focal length can be obtained.

Next, numerical examples of the present invention will be shown. In numerical examples R
(is the radius of curvature of the first lens surface from the object side of the main lens system, Dl is the thickness and air distance of the first lens from the object side of the main lens system, and N1 and vl are the object of the main lens system, respectively. These are the refractive index and Abbe number of the glass of the first lens in order from the side.

γi is the radius of curvature of the first lens surface from the object side of the auxiliary lens, D; is the first lens thickness and air gap from the object side of the auxiliary lens, and N1 and ν1 are respectively from the object side of the auxiliary lens. These are, in order, the refractive index and Abbe number of the glass of the first lens.

Regarding the aspherical surface, the shape of the aspherical surface is as follows: R is the paraxial radius of curvature that contributes to determining the focal length, A1 is the aspherical even coefficient, B1 is the aspherical odd coefficient, and ΔX is X in the optical axis direction. axis, the Y axis is perpendicular to the optical axis, the direction of light travel is positive, and when the origin is the intersection of the apex of the lens and the X axis, the aspheric surface of the lens and the spherical surface that contributes to determining the focal length are the grinding length. It is expressed as the difference in the X-axis direction from the surface.

The main lens system of the first embodiment according to the present invention is shown below.

f=100 F=1?3.5 2ω-55,64
゜Back focus = 45.61 R-: Aspherical surface A+-0,120XlOB+ = 0.427X] 0-
'4-1 A goose' 0.216X10B*=O,157X1.OA+
= 0.821X] OB+ = 0.365XIO
−10
-16A4 = 0.774X10
B4 = 0.164X10A@= 0.20
3X10-'' Next, an example will be shown in which the rear group of the main lens system of the first example is replaced with an auxiliary lens.

f=140.24 F=1:4.92ω=41.2
4" Back focus -41,17 Screen γ: Aspherical surface A+ = 0.270X11) B+ = 0.
777XIO4-6, As = 0.111XIOBm2 0.723×10
As = 0.715X10 Bs = 0.1
33X1 (1-A4 = 0.746X10-
8+ = 0.152XIO-.

f=100 1i'=l:3.52 ω-55
, 640 Back focus = 41.33 Rt; Aspherical surface A+ "" 0.489XlO-B+ = 0.8 old ×
l0-A Yukiji 0.235X10-B Goose = 0.6
93Xl (1-As = 0.207X10-
Bs = 0.470X]0-A4 = 0.91
9X10-Ba = 0.695X10A,
20, 103Xl O Next, an example will be shown in which the rear group of the main lens of the second example is replaced with an auxiliary lens.

f=14024 F=1:4.9 2ω=41.24゜pack focus=37.15 7) l! :Aspherical AI” 0.103X10- B+
= 0.667X10A =-0,129X1
0- Bs = 0.804X10-
1-7 A* = 0.708X10 Bm
= 0.135×10A4 = 0.739Xl
OB4 = 0.155X10Ag = 0.
819XIO Focusing in the variable focal length lens system according to the present invention may be performed by the entire lens system even when the entire main lens system and the auxiliary lens group are inserted.

The method of focusing by moving the front group has less variation in aberrations depending on the subject distance, and it is possible to obtain good image quality over the entire shooting distance range with a small number of lens extensions.

Even if the rear group is replaced with an auxiliary lens group, the same effect can be obtained by moving only the front group to perform focusing.

On the other hand, when the rear group is replaced with an auxiliary lens group, a method of performing focusing by moving only the auxiliary lens group is preferable because it can be performed with relatively little variation in aberrations.

As described above, according to the present invention, a compact lens system with variable focal length can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the main lens system in the first embodiment of the lens system according to the present invention, Fig. 2 is a diagram of various aberrations of the main lens system of the first embodiment with respect to an object at infinity, and Fig. 3 is a cross-sectional view of the lens when the rear group of the main lens system shown in Fig. 1 is replaced with an auxiliary lens group, Fig. 4 is a diagram of various aberrations of the lens system shown in Fig. 3 for an object at infinity, and Fig. 5 is a diagram of the main lens system. A cross-sectional view of the main lens system in the second embodiment of the lens system according to the invention, FIG. 6 is a diagram of various aberrations of the main lens system shown in FIG. 5 for an object at infinity, and FIG. FIG. 8 is a cross-sectional view of the lens when the rear group of the main lens system shown in FIG. 1st figure leaves? (Foundation)

Claims (2)

[Claims] (1) The front group and the front group have positive refractive power.
- In a lens system that includes two lens groups of the rear group, the front group is advanced and the rear group is replaced with an auxiliary lens group having a negative refractive power different from the refractive power of the rear group. A variable focal length lens system that is characterized by intermittently changing the focal length of the entire lens system. (2) The auxiliary lens group includes at least one positive lens and at least one negative lens. [J+ variable focal length lens system.