Patent ID: 7315352

Claim:
A projection optical system for digital lithography, the system comprising: an Offner imaging system defining an optical axis and having a well-corrected region; spatial light modulators circumferentially arranged about the optical axis such that optical beams emitted thereby propagate through the Offner imaging system within the well-corrected region; and a mirror system, concentric with the optical axis, arranged to direct the optical beams emitted by the spatial light modulators to propagate through the Offner imaging system within the well-corrected region in which the mirror system comprises: a frustoconical external reflective surface facing away from the optical axis, concentric with the optical axis and aligned with the well-corrected region; and a frustoconical internal reflective surface, facing the optical axis, concentric with the optical axis and further from the optical axis than the frustoconical external reflective surface, the frustoconical internal reflective surface configured to reduce the optical beams in circumferential extent and arranged to direct the reduced-extent optical beams towards the frustoconical external reflective surface.