JPH09189866A - Illumination optical system for endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely obtain uniform illumination over the wide range of an object to be observed by forming the surface of a cover lens to be a convex aspherical surface where the curvature of the peripheral part is larger than that of the central part and forming the surface thereof on a light guide side to be a concave aspherical surface where the curvature of the peripheral part is smaller than that of the central part. SOLUTION: The surface 2a of the cover lens 2 on the object side is formed to be the convex aspherical surface consisting of the aspherical peripheral part 2a' and the plane central part 2a". The surface 2b of the cover lens 2 on the light guide 1 side is formed to be the concave aspherical surface where the curvature of the peripheral part is smaller than that of the central part. By forming the surface 2a of the cover lens 2 on the object side to be the convex aspherical surface where the curvature of the peripheral part 2a' thereof is larger than that of the central part 2a", the decline of the peripheral light quantity caused by irregular reflection or total reflection caused on the inner surface of an outer periphery part is prevented. Therefore, the uniform illumination over the wide range is completely obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system for an endoscope.

[0002]

2. Description of the Related Art In a conventional illumination optical system for an endoscope of this type, a cover lens is generally arranged in front of the exit end face of the light guide, that is, on the object side to diffuse the light emitted from the light guide in a wide range. However, the light emitted from the exit end face of the light guide at a wide angle is diffusely reflected by the inner surface of the outer periphery of the cover lens and disappears, or is totally reflected by the inner surface of the outer periphery and directed toward the center of the field of view or the light guide. Therefore, there is a problem that the light distribution to the peripheral part of the visual field becomes insufficient and uniform illumination over a wide range cannot be obtained. Therefore, in order to solve such a problem, for example, it is considered that the surface on the light guide side of the cover lens (concave lens) is a composite surface including a central portion of a spherical shape and a peripheral portion of a conical shape. Was.

[0003]

However, these prior arts only change the direction of the chief ray of the light emitted from the exit end face of the light guide at a wide angle, and the outer circumference of the cover lens of the lower ray is changed. Total internal reflection at the interior surface has not yet been resolved and was therefore insufficient to obtain uniform illumination over a wide area.

The present invention has been made to solve such a problem, and an object of the present invention is not to provide an illumination optical system for an endoscope which can sufficiently obtain uniform illumination over a wide range of an observation object. It is assumed that.

[0005]

In the illumination optical system for an endoscope of the present invention which achieves the above object, a cover lens is disposed on the object side of the illumination light emitting portion, and the cover lens has a negative refracting power as a whole. And the object-side surface of the cover lens is formed from a convex aspherical surface having a larger curvature in the peripheral portion than the curvature in the central portion, and the surface on the light guide side has a peripheral portion greater than the central portion. It is characterized in that it is formed from a concave aspherical surface having a smaller curvature.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to the first embodiment shown in FIG. 1. Reference numeral 1 is a light guide, and 2 is a front side (object side) of an exit end surface 1a of the light guide 1. The cover lens is a concave lens arranged in.
The object-side surface 2a of the cover lens 2 is formed by a convex aspherical surface including an aspherical (large curvature) peripheral portion 2a 'and a planar (zero curvature) central portion 2a ". The surface 2b of the cover lens 2 on the light guide 1 side is formed as a concave aspherical surface having a smaller curvature in the peripheral portion than in the central portion.

Therefore, the light emitted from the exit end surface 1a of the light guide 1 at a wide angle has a smaller degree of light diffusion because the peripheral surface has a smaller curvature than the center on the surface 2b of the cover lens 2 on the light guide 1 side. Weakened. As a result, in addition to the principal ray A, the lower ray B blocked by the edge 3 of the cover lens 2 is also emitted as illumination light from the object side surface. And
Since the lower light beam B is not blocked by the edge portion 3, the disadvantage that the lens diameter (outer diameter) of the cover lens 2 must be increased in order to force the lower light beam B to be emitted is solved, and as a result, the cover is The outer diameter of the lens 2 can be reduced. The principal ray A and the lower ray B passing through the light guide 1 side surface 2b of the cover lens 2 are:
Both can pass through the peripheral portion 2a 'of the object side surface 2a and illuminate the peripheral portion of the visual field. In this way, the peripheral portion 2a ′ of the object side surface 2a of the cover lens 2 is formed into a convex aspherical shape having a larger curvature than the central portion 2a ″, so that the peripheral light amount due to irregular reflection or total reflection generated on the inner surface of the outer peripheral portion. Can be prevented from declining.

Thus, according to the configuration of the first embodiment,
It is possible to obtain a substantially trapezoidal light distribution characteristic without increasing the outer diameter of the cover lens and to sufficiently obtain uniform illumination over a wide range, as shown in FIG. FIG. 3 shows a second embodiment, in which the shapes of the object side surface 2a and the light guide 1 side surface 2b of the cover lens 2 disposed in front of the emission end face 1a of the light guide 1 are the same as in the first embodiment. is there. Further, the cover lens 2 in the present embodiment is composed of a heterogeneous medium lens having a higher refractive index in the peripheral portion than in the central portion. Therefore, in addition to the operation and effect of the first embodiment, the light emitted from the central portion of the emission end surface 1a of the light guide 1 can be redirected toward the peripheral portion as the light passes through the cover lens 2. In addition, it is possible to brightly illuminate the periphery of the visual field.

The cover lens 2 is manufactured by a glass mold or a plastic mold, and as a result, the manufacture is easy.

[0010]

As described above, the endoscope illumination optical system according to the present invention has an important practical advantage that uniform illumination over a wide range can be sufficiently obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a graph showing light distribution characteristics of the first embodiment.

FIG. 3 is a sectional view of a second embodiment of the present invention.

Claims (3)

[Claims] 1. An illumination optical system for an endoscope in which a cover lens is disposed on the object side of an illumination light emitting portion, wherein the cover lens has a negative refracting power as a whole, and the cover lens on the object side of the cover lens is The surface is formed from a convex aspherical surface with a larger curvature in the peripheral portion than in the central portion,
An illumination optical system for an endoscope, wherein a surface on a light guide side is formed of a concave aspheric surface having a smaller curvature at a peripheral portion than at a central portion. 2. The endoscope according to claim 1, wherein the medium of the cover lens is formed of a heterogeneous medium lens having a higher refractive index in the peripheral portion than in the central portion. Illumination optical system. 3. The cover lens is a glass mold,
Alternatively, the illumination optical system for an endoscope according to claim 1 or 2, which is formed by a plastic mold.