JPS60235112A - Image forming optical system for endoscope - Google Patents

Abstract

PURPOSE:To improve the light distribution unevenness of the periphery of a visual field to the center and to improve the durability by arranging a stop for controlling the quantity of light at a position different from a brightness stop, and constituting its island-shaped light shield part which satisfies a specific conditional expression. CONSTITUTION:The brightness stop 3 is arranged between concave and convex lenses 1 and 2 and the stop 7 for controlling the quantity of light is arranged on the composition surface of a convex lens 4 consisting of cemented convex and concave lenses 5 and 6. The island-shaped light shield part 7a of the stop 7 satisfies the specific conditional expression 2, where (r) is the radius of the island- shaped light shield part 7a, hA the height of the marginal light beam 8a of on- axis luminous flux 8, hC the height of the main light beam 9a of off-axis luminous flux 9, and hS the height of the lower light beam 9b. Consequently, part of the on-axis luminous flux 8 is cut off to reduce the intensity of a light beam reaching the center of an image plane 10, and consequently the luminous flux distributions in the center and at the periphery of the visual field are uniformed to improve luminous flux irregularity characteristic to an objective lens; and the light shield part 7a is provided in the lens, so its durability is improved.

Description

[Detailed description of the invention] Technical field The present invention relates to an imaging optical system for an endoscope.

Prior Art In order to achieve uniform light distribution between the center of the field of view and the periphery in conventional endoscopes, the outer surface of the cover glass of the illumination optical system is A semi-transparent mirror and a convex mirror were respectively formed on the inner surface of the mirror to direct the light from the center to the periphery, but this was only intended to improve the unevenness of light distribution symmetrical to the optical axis of the illumination optical system. Since this method did not improve the uneven light distribution symmetrical to the optical axis of the imaging optical system, it was not possible to improve the uneven light distribution caused by the unique properties of the objective lens. Also, in the case of the above configuration,
Since the semi-transparent mirror is formed on the outer surface of the cover glass, there is also the problem that it is susceptible to external influences and has poor durability.

Purpose: In view of the above-mentioned problems, the present invention provides an imaging optical system for an endoscope that can improve the unevenness of light distribution in the periphery of the center of the field of view caused by the unique properties of the objective lens, and also has excellent durability. We aim to provide the following.

Summary The imaging optical system for an endoscope according to the present invention has at least one light amount control diaphragm disposed at a position different from the aperture diaphragm to block a part of the axial light beam, thereby weakening the intensity of the light beam reaching the center of the image plane. This is how it was done.

EXAMPLE Below, the present invention will be described in detail based on an example shown in FIG. 1. 1 is a concave lens, 2 is a convex lens, 3 is an aperture stop provided between the concave lens l and the convex lens 2, 4 is a convex lens formed by cementing a convex lens 5 and a concave lens 6; 7;
is a light quantity control diaphragm which is provided on the cemented surface of the convex lens 4 and is composed of a circular island-shaped light shielding part 7a as shown in FIG. These constitute the objective lens of the endoscope, that is, the imaging optical system. The light shielding portion 7a has a maximum radius 'f
When r: r, the following conditions (a) and (b) are satisfied.

hA>r
)(2hc+hS)/3>'r ----------
-------(b) However, hA is the height of the marginal ray 8a of the on-axis beam 8, hC is the height of the principal ray 9a of the off-axis beam 9, and hS is the lower ray of the off-axis beam 9. The height is 9b.

Reference numeral 10 denotes an image forming surface such as an incident end surface of the image guide. The imaging optical system for an endoscope according to the present invention is configured as described above, and a part of the axial light beam 8 is blocked by the light blocking portion 7a, and the intensity of the light beam reaching the center of the image plane 10 is weakened. The light distribution between the center of the field of view and the periphery is made uniform. Therefore, it is possible to improve the unevenness of light distribution in the periphery with respect to the center of the field of view, which is caused by the characteristics peculiar to the objective lens. Furthermore, since the light shielding portion 7a is formed inside the objective lens, it is not affected by external influences and has excellent durability.

FIG. 2 shows a second embodiment, in which 11 is a convex lens formed by bonding a glass block 12 and a convex lens 13;
is a brightness diaphragm provided on the cemented surface of the convex lens 11, 15
16 is a convex lens, and 16 is a ring as shown in FIG. 2(B), which is provided on the object side of the convex lens 15 and is used to block the marginal ray 8a of the axial ray 8, its vicinity, and a part of the off-axis ray 9. It is a light quantity control diaphragm made of a band-shaped light shielding part 16a, and these constitute an objective lens. and,
The light shielding part 16a satisfies the following conditions (c) and (d) when its minimum radius is rmjx and its maximum radius is l'm4.

hA> r=n −−−−−−−−−−−(c)(2
hO+hS)/3>rmχ−−−−−−−−−−−−(
d) However, hA is the height of the marginal ray 8a of the axial principal ray 8, hC is the height of the principal ray 9a of the off-axis beam 9, and hS is the height of the lower ray 9b of the off-axis beam 9.

In this embodiment as well, a part of the axial light beam 8 is blocked by the light shielding part 16a and the intensity of the light beam reaching the center of the image plane 10 is weakened, so this problem occurs due to the characteristics peculiar to the objective lens, as in the first embodiment. It is possible to improve the unevenness of light distribution in the periphery with respect to the center of the visual field.

Furthermore, it has excellent durability for the same reason as the first embodiment. Furthermore, the diaphragm 16 has a ring-like hollow light shielding part 16a.
Since it also blocks a part of the off-axis light beam 9, it also has the advantage of increasing the depth of focus at the center.

FIG. 3 shows a third embodiment, which includes a convex lens 1
The above conditions (a) and (b) provided on the side surface of the object in No. 5
The island-shaped light shielding portion 17a that satisfies the above conditions (C) and (d)
), and the light amount control diaphragm 17 is composed of an annular light shielding part 17b that satisfies the following.Other configurations are the same as those of the second embodiment.

FIG. 4 shows a fourth embodiment, which includes a convex lens 1
An island-like light-shielding portion 18a that satisfies the above conditions (a) and (b) is provided on the image side surface of No. 3, and an annular light-shielding portion that satisfies the above-mentioned conditions (c) and (d) is provided on the object side surface of the convex lens 15. The second embodiment has a light amount control diaphragm 18 consisting of a portion 18b, and the other configurations are the same as those of the second embodiment.

Effects of the Invention As described above, the imaging optical system for an endoscope according to the present invention can improve the unevenness of light distribution in the periphery with respect to the center of the visual field, which is caused by the unique properties of the objective lens, and is also excellent in durability. It has this important advantage.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the imaging optical system for an endoscope according to the present invention, and FIGS. 2 to 4 are diagrams showing second to fourth embodiments, respectively. l... Concave lens, 2, 4... Convex lens, 3...
... Brightness aperture, 7... Light amount control aperture, 8...
- On-axis light flux, 9... off-axis light flux, lO... imaging plane. No. 1 (A) L9 ( ” 2nd F (A) 1゜ (B) [ (B) Ward button ■ Procedural amendment (voluntary) August 6, 1985 Commissioner of the Japan Patent Office 1, Indication of case Patent application Sho 5!11-91096 No. 2, Title of invention Imaging optical system for endoscope 4, Agent 〒1
05 19 Shinbashi 5, Minato-ku, Tokyo Phone Tokyo (432) 4
576 (65B2) Patent Attorney Yasushi Shinohara 5, Detailed explanation of the invention in the specification subject to amendment. Expand v:,/i”
) 6. Contents of amendment + 11 "Unexamined Japanese Patent Application Publication No. 1983-1980" on page 2, lines 16-17
3184" is corrected to "Japanese Patent Application Laid-open No. 5'l-31834." (2) [ru] on page 4, line 18 of the specification box. According to the present invention
...as stated above" is corrected to the following sentence. Note that if r exceeds hA, all the axial light flux will be blocked, and the center will become dark. Therefore, the above condition fat is intended to allow the minimum amount of light to pass through. Formula % Formula %: 1 : This is a formula that divides the luminous flux internally into 2. In other words, by this formula, at least 2/3 of the off-axis luminous flux can be secured.Even if it is less than 2/3, the on-axis luminous flux can be balanced and brightness can be achieved. Although it is possible to achieve uniform brightness, it is not good because the entire surface becomes dark.Therefore, the above condition (b) is intended to ensure the minimum brightness of the entire surface. The mirror imaging optical system is as described above.'' (3) Insert the following sentence between lines 3 and 4 on page 6 of the specification box. "The above condition tel is for blocking a part of the axial luminous flux 8 in order to achieve the intended purpose. Also, the above condition (di means the above condition (b) and (4) "Part of the 1st off-axis light beam 9 on page 6, lines 11-12 of the specification" is corrected as the peripheral part j of the r-axis on-axis light beam 8. (5) Specification tube 6 Insert the following sentence between lines 19 and 200 of the page: "In this example, the light flux can be gradually cut from on-axis to off-axis, so the brightness can be uniformed evenly over the entire image plane. J (6) Insert the following sentence between lines 6 and 7 on page 7 of the specification box. Increasing the number of surfaces increases the degree of freedom in the position of limiting on-axis and off-axis light beams, which has the advantage of further optimizing brightness uniformity.

Claims (4)

[Claims] (1) An imaging optical system for an endoscope, comprising at least one light amount control diaphragm that blocks a part of the axial light beam, disposed at a position different from the aperture diaphragm. (2) The imaging optical system for an endoscope according to claim (1), wherein the light amount control diaphragm comprises an island-shaped light-shielding portion that satisfies the following conditions. (a) hA>r (b) (2ha + hs)/3>rHowever,
hA is the marginal ray height, hC is the off-axis chief ray height, ll
s is the off-axis lower ray height, and r is the maximum radius of the light shielding part of the aperture. (3) The imaging optical system for an endoscope according to claim (1), wherein the light amount control diaphragm is comprised of an annular light-shielding portion that satisfies the following conditions. (e) hA > r-ty (d) (211c + hS) / 3 > r 2
zHowever, hA is the marginal ray height, 'Inc is the off-axis chief ray height, 11s is the off-axis lower ray height, rm・- is the minimum radius of the light-shielding part of the aperture, and T is the maximum radius of the light-shielding part of the aperture. It is. (4) An island-shaped light-shielding part that satisfies the above conditions (a) and (b), in which the light amount control aperture is provided on the same or different surfaces, and an annular light-shielding part that satisfies the above-mentioned conditions (c) and (d). Claim (1) characterized in that it consists of:
The imaging optical system for an endoscope described in .