Endoscope

1. An endoscope comprising:

a first image pickup optical system that is disposed in an insertion portion to be inserted into a lumen and for observing an observation object in a first observation direction;

a second image pickup optical system that is disposed in the insertion portion and for observing an observation object in a second observation direction which is different from the first observation direction;

a light guide that guides illumination light emitted from a light source to the insertion portion;

an illumination optical system that is disposed in the insertion portion and includes a ring-shaped portion for illuminating the first observation direction;

an incident surface that is provided to the illumination optical system, is in contact with an end surface of the light guide to receive the illumination light, and formed orthogonal to a longitudinal direction of the insertion portion; and

two reflecting surfaces that are disposed at a position opposite to the incident surface, the two reflecting surfaces having inclinations in two directions with respect to a surface orthogonal to the longitudinal direction of the insertion portion, disposed so as to face each other, the two reflecting surfaces reflecting the illumination light incident from the light guide to the incident surface toward directions along tangent lines of the ring-shaped portion of the illumination optical system, to cause the illumination light incident to inside of the illumination optical system.

2. The endoscope according to claim 1 , wherein the illumination optical system includes an optical processing portion that reflects the illumination light guided from the light guide toward inside of the illumination optical system, the optical processing portion being provided in a position including an inner circumferential surface of the illumination optical system.

3. The endoscope according to claim 2 , wherein the optical processing portion is provided in a site other than a region from which the illumination light that is guided from the light guide and incident to the illumination optical system is emitted in the longitudinal direction of the insertion portion.

4. The endoscope according to claim 1 , wherein the illumination optical system includes a light-guiding portion that causes the illumination light guided by the light guide to be incident to the ring-shaped portion.

5. The endoscope according to claim 1 , wherein the illumination optical system is disposed to surround an outer circumference side of the first image pickup optical system.

6. The endoscope according to claim 1 , further comprising:

a second light guide that guides the illumination light emitted from the light source to the insertion portion; and

a second illumination optical system including a prism that changes an orientation of the illumination light guided from the second light guide and causes the illumination light to be emitted toward the second observation direction, the prism at the same time causing a part of the illumination light to be emitted toward the first observation direction.

7. The endoscope according to claim 6 , wherein

the first image pickup optical system, the second image pickup optical system, and the second illumination optical system are substantially coaxially provided, and are formed to each include a circle-shaped outer circumferential portion, and

the second image pickup optical system, the second illumination optical system, and the second light guide are disposed so as to satisfy a relation of RB>RC>RA, where

RA represents a distance from an optical axis of the first image pickup optical system to an outermost circumferential surface of the second image pickup optical system;

RB represents a distance from the optical axis of the first image pickup optical system to an outermost surface of the second illumination optical system; and

RC represents a distance from the optical axis of the first image pickup optical system to an outside outer circumferential surface of the second light guide.

8. The endoscope according to claim 6 , wherein

the first image pickup optical system, the second image pickup optical system, and the second illumination optical system are substantially coaxially provided, and are formed to each include a circle-shaped outer circumferential portion, and

the second image pickup optical system, the second illumination optical system, and second light guide are disposed so as to satisfy a relation of RB>RA>RC, where

RA represents a distance from an optical axis of the first image pickup optical system to an outermost circumferential surface of the second image pickup optical system;

RB represents a distance from an optical axis of the first image pickup optical system to an outermost surface of the second illumination optical system; and

RC represents a distance from an optical axis of the first image pickup optical system to an outside outer circumferential surface of the second light guide.

9. The endoscope according to claim 6 , wherein the light guide is provided so as to be adjacent to an outer circumference of the second image pickup optical system and parallel with the longitudinal direction of the insertion portion.

10. The endoscope according to claim 1 , wherein

the first observation direction is a forward observation direction of the insertion portion, and the second observation direction is a sideward observation direction of the insertion portion, and

the first image pickup optical system is disposed on a distal end side of the insertion portion and forms an image of an observation object in a forward direction of the insertion portion, and the second image pickup optical system forms an image of an observation object in a sideward direction of the insertion portion.

11. The endoscope according to claim 1 , wherein

the first image pickup optical system includes a first objective lens, and the second image pickup optical system includes a second objective lens, and

the second objective lens is disposed on a proximal end side of the insertion portion with respect to the first objective lens.

12. The endoscope according to claim 1 , wherein the illumination optical system includes a diffusing portion provided on a surface on the proximal end side of the insertion portion, the diffusing portion scattering the illumination light and causes the scattered illumination light to be emitted forward the insertion portion.

13. The endoscope according to claim 12 , wherein the diffusing portion is formed to have varying diffusibility such that the farther from the light guide, the greater a diffusing effect of the illumination light becomes.

14. The endoscope according to claim 1 , wherein an inclined surface or a smooth curved surface oriented forward and toward an optical axis side is formed on a front surface side of an outer circumferential edge portion of the ring-shaped portion in the illumination optical system.