An aberration changing optical system to be used with a projection optical system of a projection exposure apparatus, includes an optical element having at least one of a cylindrical surface and a toric surface and being rotatable about and tiltable to an optical axis of the optical system. In another...http://www.google.fr/patents/US6924937?utm_source=gb-gplus-shareBrevet US6924937 - Aberration correcting optical system
