JPS6290610A - Focal length conversion lens system with shared diaphragm - Google Patents

Abstract

PURPOSE:To correct various aberrations excellently and to share a diaphragm by using a lens system in which plural lenses share the one diaphragm so that specific requirements are satisfied. CONSTITUTION:A standard lens consists of a convex lens 2, a concave lens 3, a convex meniscus lens 4, and a biconvex lens 5 from an object side and a telephoto lens consists of a convex lens 6, a biconvex lens 6, a biconcave lens 7, and a biconvex lens 8 from the object side. Then, those lenses meet the specific requirements and then while the plural lenses are used, only one diaphragm is required. Consequently, the structure of each lens is simple, the size is reduced, and the performance of each lens is held high.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a focal length conversion lens system that shares an aperture,
In particular, it relates to optimal lens system data for a 2/3-inch image pickup tube (tentative).

[Prior art]

There are various methods for changing the focal length of a lens, but the typical ones other than zoom lenses are A, front converter type, B, rear converter type, and C1.
An example is a multiple lens conversion formula.

However, type A cannot have a large focal length ratio, is large in size, heavy in weight, and has insufficient optical performance.

Type 8 has a large (dark) F number when telephoto, and its optical performance is inadequate. Furthermore, the 0 type requires a diaphragm for each, making the mechanism complicated.

As described above, each method has its problems, and both methods A and B are difficult to put into practical use, especially when image quality at telephoto is required.

[Purpose of the invention]

Therefore, it is an object of the present invention to provide a focal length conversion lens system that uses a shared aperture in which various aberrations are well corrected by employing the 0 type in which one aperture is shared by a plurality of lenses.

[Structure of the invention]

In the present invention, one aperture is shared by multiple lenses with different focal lengths, and the standard lens uses a front aperture type lens, and the telephoto lens uses a rear aperture type lens, so that the aperture position is constant from the focal plane. The configuration data of each lens is set so as to satisfy the condition that the lens is at a distance of .

〔Example〕

Hereinafter, the lens system of the present invention will be explained based on preferred embodiments.

FIG. 1 shows a first embodiment of the lens system of the present invention, and is an optical cross-sectional view (
A) and an optical cross-sectional view (b) of a telephoto lens inserted into the photographing optical path in place of the standard lens during telephoto shooting, and the position of the diaphragm 1 does not change during this insertion and removal.

A standard lens is a convex lens when viewed from the subject side, a concave lens 3
, convex meniscus lens 4 and biconvex lens! Similarly, the telephoto lens consists of a convex lens 6, a biconcave lens 7, and a biconvex lens 8 when viewed from the subject side, and consists of the following data.

Example (1) Standard lens surface r d Nd
ν aperture 1.56 1 13.000 3.71 1.7725 49.6 3 -11.198 0.91 1.7408 27.7 8 -49.785 f=18. oI Bf=12.9j F/Number 1
．． Distance between 6 aperture and focal plane 28.86 Angle of view 34° Telephoto lens surface r d Nd
Aperture f=45.01. Bf (from aperture) = 28.86F/
Number: 2.7 Angle of view: 14 degrees, where γ is the radius of curvature, d is the interval, Nd is the refractive index, ν is the Abbe number, r is the focal length of the entire system, and Bf is the bank focus.

In the lens of Example (1), the distance from the aperture to the focal plane is 28.86 +n in the standard state, and this distance is set to be exactly the same in the telephoto state, thus satisfying the above-mentioned condition for the aperture position.

This way, you can avoid using multiple lenses! However, since only one diaphragm is required and a mechanism for moving the diaphragm can be omitted, it is also advantageous in terms of cost.

Please note that the F number changes depending on the lens switching.
This is no problem at all since it can be easily corrected using the camera's exposure control mechanism.

FIG. 2 shows various aberrations in this Example (1).

FIG. 3 shows a second embodiment of the lens system of the present invention, and is an optical cross-sectional view (
A) and an optical cross-sectional view (b) of a telephoto lens inserted into the photographing optical path in place of the standard lens during telephoto shooting,
The position of the aperture 1 does not change during this insertion and removal.

The standard lens has 2 convex lenses and 3 concave lenses when viewed from the subject side.
, consisting of a convex meniscus lens 4 and a biconvex lens 5,
The telephoto lens also includes a convex meniscus lens 6, a concave meniscus lens 7, a concave lens 8, and a biconvex lens 9 when viewed from the subject side, and consists of the following data.

Example (2) Standard lens surface r d, Nd
ν aperture f=16.50 8f=13.53 F/number 1.
Distance between 6th aperture and focal plane 27.64 Angle of view 37° Telephoto lens surface γ d Nd
ν stage f45.01 8f (from aperture) 27.64F/number 2
．． 7. Angle of view: 14° Various aberrations in this Example (2) are shown in FIG.

〔Effect of the invention〕

As described above, according to the data of the present invention, the structure of each lens can be made simple and compact, and the performance of each lens can be maintained at a high level.

Furthermore, since there is no need to move the diaphragm mechanism, the structure does not become complicated, which is very advantageous in terms of space, reliability, and cost.

[Brief explanation of drawings]

FIG. 1 shows the first embodiment of the lens system according to the present invention.
A), Optical cross-sectional view at telephoto mode (B), FIG. 2 is an aberration characteristic diagram of the first embodiment, and FIG. 3 shows the second embodiment of the lens system of the present invention at standard time (A), at telephoto mode. The optical cross-sectional view in (b) and FIG. 4 show aberration characteristic diagrams of the second embodiment, respectively. :AlI 3 people Fuji Photo Koki Co., Ltd.! (b) Mark 2P meeting 1 %2 figure

Claims (1)

[Scope of Claims] (1) A focal length conversion lens system that shares a diaphragm and is composed of a standard lens and a telephoto lens that move forward and backward into the photographing optical path before and after the diaphragm, characterized by comprising the following data: lens system. Standard lens surface Radius of curvature γ Distance d Refractive index Nd Abbe number ν Aperture 1.56 1 13.000 3.71 1.7725 49
．． 62 -211.765 2.88 3 -11.198 0.91 1.7408 27
．． 74 15.425 1.35 5 -12.685 2.70 1.6204 60
．． 36 -7.736 0.23 7 15.659 2.55 1.6600 58
．． 38 -49.785 f=18.01 Bf=12.97 F/No.1.6 aperture to focal plane distance 28.86 Angle of view 34° Telephoto lens surface Radius of curvature γ Distance d Refractive index Nd Abbe number ν1 16.583 4.23 1.6968 56
．． 52 8333.333
4.68 3 -32.463 3.30 1.6727 32
．． 24 13.455 6.75 5 37.895 3.15 1.6516 58
．． 56 -28.176 1.02 Aperture f=45.01 Bf (from aperture)=28.86F/No
2.7 Angle of view: 14°, where f represents the total focal length and Bf represents the back focus. (2) A focal length conversion lens system that shares a diaphragm and is composed of a standard lens and a telephoto lens that move forward and backward into the photographing optical path with the diaphragm as a boundary, and is characterized by having the following data. Standard lens surface Radius of curvature γ Distance d Refractive index Nd Abbe number ν Aperture 1.43 1 13.810 2.97 1.7725 49.
62 -99.278 2.64 3 -10.141 0.83 1.7408 27.
74 17.523 1.24 5 -12.329 2.81 1.6204 60.
36 -7.829 0.21 7 18.523 1.98 1.6600 58.
38 -25.204 f=16.50 Bf=13.53 Distance between F/No.1.6 aperture and focal plane 27.64 Angle of view 37° Telephoto lens surface Radius of curvature γ Distance d Refractive index Nd Abbe number ν1 16.901 2.70 1.6180 63.
42 56.250 0.45 3 22.401 4.50 1.6204 60.
34 27.926 4.68 5 -51.136 1.35 1.6990 30.
06 11.662 5.22 7 23.208 3.15 1.6584 50.
88 -30.670 1.01 Aperture f=45.01 Bf (from aperture)=27.64F/No.
2.7 Angle of view: 14°, where f represents the total focal length and Bf represents the back focus.