Patent ID: 8908151

Claim:
An illumination optical system which illuminates a surface to be illuminated with light from a light source, the illumination optical system comprising: a distribution forming optical system including a fly's eye integrator having a plurality of optical surfaces arranged along a plane crossing an optical axis of the illumination optical system and forming a predetermined pupil intensity distribution behind the fly's eye integrator; and a light shield member arranged on a predetermined surface in an optical path behind the fly's eye integrator, the light shield member having a dimension along an optical axis direction longer than a dimension along a direction perpendicular to the optical axis direction to attenuate a first light toward a first point on the surface to be illuminated and attenuate a second light toward a second point on the surface to be illuminated, wherein the first attenuation rate and the second attenuation rate are different, wherein the first light passes the predetermined surface with a first angle with respect to the optical axis, the second light passes the predetermined surface with a second angle, different from the first angle with respect to the optical axis, and the second point is different from the first point on the surface to be illuminated.