Patent ID: 8237918

Claim:
An optical system having an optical axis, the optical system comprising: a polarization compensator comprising a first polarization-modifying partial element; and a first manipulator capable of moving the first partial polarization-modifying element; wherein: the optical system has a region that is in a plane perpendicular to the optical axis of the optical system; the optical system has a first illumination setting in which an intensity of light from a light source over the region does not exceed 20% of a maximum intensity in the plane; the optical system has a second illumination setting configured so that, if the light source emitted light when the optical system is in the second setting, the region would be principally illuminated with light from the light source; the first manipulator is arranged in the region so that if the light source emitted light when the optical system is in the second illumination setting, the first manipulator would be illuminated by the light from the light source; and the optical system is an illumination device configured to be used in a microlithographic projection exposure apparatus, or the optical system is a projection objective configured to be used in a microlithographic projection exposure apparatus.