Patent ID: 7087014

Claim:
An endoscope system comprising: an endoscope having an insertion tube; a main light source; an auxiliary light source comprising a white LED; and a fiber-optic light guide provided in said insertion tube, said fiber-optic light guide being provided with an incident end face which selectively faces one of said main light source and said auxiliary light source, and an exit end face which faces an illuminating optical system provided at a distal end of said insertion tube, said incident end face of the fiber-optic light guide normally facing said main light source and facing said auxiliary light source in the event of failure of said main light source, wherein said auxiliary light source is movable between a retracted position where said auxiliary light source is spaced from a position at which said auxiliary light source faces said incident end face of said fiber-optic light guide, and an operating position where said auxiliary light source faces said incident end face of said fiber-optic light guide, said auxiliary light source remaining in said retracted position when said main light source is ON and moving to said operating position in the event of failure of said main light source, wherein a positive lens is positioned in front of said white LED so that said positive lens is positioned between said white LED and said incident end face of said fiber-optic light guide when said white LED is in said operating position, and in which light rays emitted from said white LED are converged through said positive lens to be incident on said incident end face of said fiber-optic light guide, such that an optical axis of said white LED is coincident with both an optical axis of said positive lens and an axis of said fiber-optic light guide when said white LED is in said operating position, and wherein the following relationships are satisfied: r 1 ≧b ×tan θ 1 ( a−c )tanθ 2 =r 2 θ 3 ≧θ 2 wherein “a” designates the image distance of said positive lens; “b” designates the object distance of said positive lens; “c” designates the distance between a principle plane of said positive lens and said incident end face of said fiber-optic light guide; “r 1 ” designates the radius of said positive lens; “r 2 ” designates the radius of said incident end face of said fiber-optic light guide; “θ 1 ” designates the exit angle of said light rays emitted from said white LED; “θ 2 ” designates the angle of incidence of light rays which emerge from said positive lens to be incident on said incident end face of said fiber-optic light guide; and “θ 3 ” designates the threshold angle of incidence of light rays on said incident end face which are transmittable through said fiber-optic light guide.