The invention relates to an optical system of a microlithographic projection exposure apparatus, comprising at least one mirror arrangement having a plurality of mirror elements which are adjustable independently of one another for the purpose of changing an angular distribution of the light reflected by the mirror arrangement, and a polarization-influencing optical element, which generates, for impinging light having a constantly linear or a circular input polarization distribution, an output polarization distribution having a direction of polarization that varies continuously over the light beam cross section.