Patent ID: 7477458

Claim:
An illumination optical system for illuminating an object with light from a light source device comprising a plurality of optical surfaces, at least one of which is formed as a roughened surface and is arranged in a position other than closest to the object, wherein, assuming that a total quantity of light emitted to the object by the illumination optical system is L, and a total quantity of light is L 0 emitted by a reference optical system in which all the roughened surfaces of the illumination optical system are replaced with polished surfaces, the illumination optical system satisfies the following condition: 0.70≦X≦0.95, where X=L/L 0 , wherein the illumination optical system comprises, in order as viewed from an object side, a single lens having a positive power and a single fiber, and wherein assuming that a maximum value of an area of a section of an optical member constituting the illumination optical system is Sx, the section being vertical to an optical axis, and a length of the single fiber in an optical axis direction is dr, the following condition is satisfied: √{square root over (Sx)}/dr <1.