The disclosure relates to an optical system of a microlithographic projection exposure apparatus and to a microlithographic exposure method. An optical system of a microlithographic projection exposure apparatus includes an image rotator, which is arranged in the optical system such that light impinging on the image rotator is at least partially polarized. The image rotator rotates, for light impinging on the image rotator, both the intensity distribution and the polarization distribution of through a given angle of rotation.