A catadioptric projection optical system for projecting an image of an object onto an image plane through two intermediate image formations. The catadioptric projection optical system includes a first optical system, for receiving light from the object, including a plurality of lenses, a second optical...http://www.google.com.au/patents/US7092168?utm_source=gb-gplus-sharePatent US7092168 - Projection optical system and projection exposure apparatus
