A microlithographic projection imaging system has an illuminator optical system and an objective imaging system, and an adjustable profiler or energy distributor in the illuminator optical system varies the numerical aperture of the illuminator, for varying the partial coherence of the projection imager....http://www.google.com.au/patents/US5383000?utm_source=gb-gplus-sharePatent US5383000 - Partial coherence varier for microlithographic system
