Patent ID: 7118229

Claim:
An illumination optical system for illuminating a predetermined illumination area comprising: a light source; a lens array including a plurality of small lenses for dividing light emitted from the light source into a plurality of light bundles; a superimposing lens system for superimposing the plurality of light bundles on the predetermined illumination area; and a base frame that mounts a plurality of optical components disposed at least on a light path from the lens array to the superimposing lens system, the base frame including a positioning section for positioning at least the superimposing lens system, and is capable of being used in common for another illumination optical system, wherein the superimposing lens system comprises at least two lenses including a first lens and a second lens, the first lens being provided at a position nearest to the light source and mainly determining an F-number of the illumination optical system, and the second lens being provided at a position furthest form the light source and mainly determining a magnification of the illumination optical system, and wherein the F-number and the magnification of the illumination optical system are capable of being changed by replacing the first and second lenses with other lenses having different focal lengths, without changing the position of the first and second lenses in the base frame.