Patent ID: 8451430

Claim:
An illumination optical system for illuminating an illumination target surface with light from a light source, comprising: an optical integrator which forms a predetermined light intensity distribution on an illumination pupil plane in an illumination optical path of the illumination optical system with incidence of the light from the light source thereinto; a first transmission filter arranged in an optical path of a first illumination beam passing through a first region in the illumination pupil plane and having a transmittance characteristic varying according to angles of incidence of the light; a second transmission filter arranged in an optical path of a second illumination beam passing through a second region different from the first region in the illumination pupil plane and having a transmittance characteristic varying according to the angles of incidence of the light; and a rotation mechanism which rotates the first and second transmission filters so as to vary an angle of inclination thereof relative to an optical axis of the illumination optical system.