Patent ID: 7575328

Claim:
An illumination optical system for illuminating a surface to be illuminated comprising: a light beam from a light source, wherein the light beam from the light source is split in a first plane which is parallel to the optical axis of the illumination optical system, a plurality of first source images are formed in a first light source image zone with the use of the thus split light beams, and light beams from the plurality of first light source images are led to the surface to be illuminated, the light beam from the light source is split in a second plane which is parallel to the optical axis of the illumination optical system and which is perpendicular to the first plane, a plurality of second source images are formed in a second light source image zone with the use of the thus split light beams, and light beams from the plurality of second light source images are led to the surface to be illuminated, and wherein the width W 1 of the first light source image zone in the first plane and the width W 2 of the second light source image zone in the second plane satisfy the following condition: W 2 /W 1 <0.8.