Illumination system for a microlithography projection exposure apparatus, microlithography projection exposure apparatus comprising such an illumination system, and fourier optical system

An illumination system for a microlithography projection exposure apparatus for illuminating an illumination field with the light from a primary light source has a variably adjustable pupil shaping unit for receiving light from the primary light source and for generating a variably adjustable two-dimensional intensity distribution in a pupil shaping surface of the illumination system. The pupil shaping unit has a Fourier optical system for converting an entrance beam bundle entering through an entrance plane of the Fourier optical system into an exit beam bundle exiting from an exit plane of the Fourier optical system. The Fourier optical system has a focal length fFOS and a structural length L measured between an entrance-side first system surface and an exit-side last system surface along an optical axis, where (L/fFOS)