Patent ID: 8118734

Claim:
An endoscope illumination optical system comprising: a surface light source, a positive first lens element, and a positive second lens element, in this order from said surface light source, wherein said endoscope illumination optical system satisfies the following conditions: 0.40 <f/D< 0.53 0.40<0.5 ·D·θ< 0.56 wherein: f designates a combined focal length of said positive first lens element and said positive second lens element, D designates a maximum diameter of said surface light source, R 1 designates a radius of curvature of a first surface of said positive first lens element facing toward said surface light source, R 2 designates a radius of curvature of a second surface of said positive first lens element facing toward a surface to be illuminated, n 1 designates a refractive index of said positive first lens element, d 1 designates a thickness of said positive first lens element, and θ designates an angle defined as (1+0.85d 1 /R 2 )(1−1/n 1 )/R 1 −1.05/R 2 .