An optical system, in particular of a microlithographic projection exposure apparatus, includes an optical system axis and a polarization-influencing optical arrangement, wherein said arrangement has a polarization-influencing optical element which includes an optically active material having an optical crystal axis and is of a thickness profile which varies in the direction of said optical crystal axis, and a position manipulator for manipulation of the position of said polarization-influencing optical element, wherein the polarization manipulator is adapted to cause rotation of the polarization-influencing optical element about an axis of rotation, wherein said axis of rotation is arranged at an angle of 90°±5° relative to the optical system axis.