JPS6076711A - Optical system for binoculars constituted to shorter overall length - Google Patents

Abstract

PURPOSE:To enable provision of an optical system for binoculars which shortens the focal length of an objective lens and is constituted to the shorter overall length by inserting a lens having a negative focal length between the convex- concave two-element type achromatic objective lens and the incident face of the 1st prism. CONSTITUTION:A lens 4 having a single or double negative focal lengths is inserted between a convex-concave two-element type achromatic objective lens 1 and the incident face of the 1st prism 2, between the exit face of the 1st prism 2 and the incident face of the 2nd prism 3 or between the exit face of the 2nd prism 3 and the image plane of the objective system, by which the objective lens system having about 3.2Xphi focal length is obtd. The 1st prism 2 having an optical path length increased by about 20% as compared to the optical path length of the 2nd prism 3 is further provided, by which the distance from the incident point of the lens 1 up to the exit point of an eyepiece lens 5, i.e., the overall length, is made shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical system for binoculars that has a shorter overall length. It represents the provision of a shorter binocular optical system to the market, with a convex and concave two-blade type (C) between the erasure objective lens l and the entrance surface of the first prism 2 or the exit surface of the first prism 2. The approximately The first prism 2 has an optical path length that is approximately 20% larger than the optical path length of the second prism 3 in combination with an objective lens system having a focal length of 32×φ. This is based on the optical system of binoculars.

There are two types of commonly used binoculars: the Porro prism type ((a) in Figure 1) and the Dono prism type (shown in Figure 1). 38×
Given the total length of φ, φ is the effective aperture of the objective lens, which is the L7'r value).

That is, when the overall length is required to be shortened depending on the purpose, shortening the focal length ξ of the objective lens is a simple method that is directly connected to the above purpose.
There are drawbacks such as the performance of the W element (for example, spherical aberration, chromatic aberration, etc.) being significantly reduced, but if this is replaced with the optical system according to the present invention, two drawbacks (d) cannot be eliminated. It is possible to obtain a shorter binocular optical system.

Next, we will explain the details using a binocular hoko with a magnification of 7, aperture of 50, and a viewing angle of 7° as an example (see Figure 3).In the figure, a coined achromatic 1-objective lens with 01/2 convex and concave lenses cemented together. address)
between the objective lens G1/2 and the entrance surface J- of the first prism P1, or the first prism P1. It is usually inserted at a position between the exit surface of the second prism P2 and the entrance surface of the second prism P2, or between the objective system image plane (also called a stopper) on the exit surface of the second prism 1) and 2. It is a single or single compound lens with a negative focal length, and in the example of Fig. 3, it is inserted behind the objective lens.
Indicate the case. This lens has a focal length of approximately 18φ, so the objective lens (1/2) and corner lens G are combined to form an objective lens with a positive focal length of approximately 32×φ. It has a focal length of 32 x φ and provides a good image plane. Figure 4 shows that the convex and concave achromatic lens has a focal length of 32 x φ. show.

The above-mentioned insertion lens can be used as a single lens, but in that case, it is necessary to maintain the element i in the 1st order range.

Radius of curvature of first surface 1-9φl<111.11<l
-I Bφ1 radius of curvature of second surface 19φ de l R2
1] 8φ1 Note that R, 1, and R2 indicate the radius of curvature of G3.

Refractive index of glass used: 1. , 5 < nd < 1.65 (
nd is the refractive index at 5876A) Then, the inserted negative lens G3 is changed to the objective lens G1/
If the first prism P1 is placed in front of the entrance plane, the optical path length of the first prism P should be set to the optical path length of the second prism P2 so as not to obstruct the optical path exiting from the objective lens. Although it is necessary to increase the distance by about 20 inches, it is also possible to reduce the length from the front surface of the objective lens G1/2 to the image plane. Next, since the focal length of the synthetic objective lens is 32 x φ and the focal length of the objective lens of regular 7 x 50 binoculars is about 38 φ, it is necessary to shorten the focal length of the eyepiece as well. ) model of eyepiece is used] This results in unsuitable points.

For example, at the same viewing angle, the tightening r (usually called the eye point) becomes shorter, so it is necessary to use a lens with a good image η and a relatively long eye point. In this example, a four-piece type with a long eye point is used. In addition, FIG. 5 shows an example of the present invention. The optical system obtained from FIG. 3 shows an example of the present invention, and a commercially available 7
This is an example of a tracking aberration diagram of the objective optical system with normal elements and an aberration comparison table of the entire system.

According to the invention According to general elements Objective system aberration Objective system aberration SI8 Spherical aberration C! 6563A SIC sine condition d 5876tr F4861〃 Figure 5 Table Jl-1 Comparison of tracking aberration values for the entire optical system.

Aberration value comparison table Note) Optical system aberrations of general elements are not specific. DP: Diopter

[Brief explanation of drawings]

The drawings relate to the optical system of the present invention, and (a) in FIG. 1 shows an example of the optical system of porroprism binoculars, and (b)
An example of the optical system of Kedaha prism type binoculars, Fig. 2 shows the optical system according to the present invention, Fig. 3 shows an example of 7 x 50.7° (49) 0, and Fig. 4 shows a comparison diagram. Number 1 in the diagram: Objective lens 2: First prism 3
. . . Second prism 4. Negative focal length lens according to the present invention 5. Eyepiece lenses are shown respectively. Patent applicant Katsuma Optical Machinery Co., Ltd. Representative Seiji Katsuma (4) ();71 included z t! 'X Preliminary I Phantom Procedural Amendment 1978, -', 2F Ya-Japanese Patent Office Commissioner Kazuo Wakasugi 1, Indication of Case Patent Application No. 185309 of 1982 2
Title of the invention: Optical system for binoculars with a shorter overall length 3; Relationship with the person making the correction Patent applicant address: 1-27-175 Wakagi-cho, Itabashi-ku, Tokyo Date of amendment order: January 31, 1980 6. Subject of amendment Specification

Claims (1)

[Claims] Between the concave and convex two-piece achromatic objective lens 1 and the entrance surface of the first prism 20, and between the exit surface of the second prism 2 and the second prism 3.
or between the exit surface of the second prism 3 and the image plane of the objective system. The total length of the first prism 2, which has an optical path length approximately 20% larger than the optical path length of the second prism 3, together with the objective lens system having a The distance to the exit point of the tangential 1111 lens is b
A binocular optical system with a shorter structure.