Patent ID: 8154707

Claim:
An illumination optical system for illuminating an object surface by condensing light from a light source and forming a light-condensing point, said illumination optical system comprising, in order from a side of the light source: a first switching optical system and a second switching optical system switchably inserted into an optical path of said illumination optical system; and a movable optical system movable in a direction of an optical axis of said illumination optical system and moving along the optical axis to vary an irradiated area on an incident surface of means for forming a secondary light source, wherein power of said second switching optical system is larger than power of said first switching optical system, wherein the light-condensing point is formed at a side of the object surface relative to said movable optical system when said first switching optical system is inserted in the optical path, and the light-condensing point is formed at the side of the light source relative to said movable optical system when said second switching optical system is inserted in the optical path, and wherein a shape of the irradiated area in the incident surface is maintained through a state that the first switching optical system is inserted into the optical path and a state that the second switching optical system is inserted into the optical path.