The invention relates to an optical system, in particular of a microlithographic projection exposure apparatus, with a polarization-influencing optical arrangement. In accordance with one aspect of the invention, this polarization-influencing optical arrangement comprises: at least one polarization-influencing optical element, which consists of an optically active material with an optical crystal axis and has a thickness profile that varies in the direction of this optical crystal axis, at least one lambda/2 plate; at least one rotator, which causes a rotation of the polarization direction of light incident on the rotator about a constant polarization rotation angle, and an actuator apparatus, by which the lambda/2 plate and the rotator can be moved independently of one another between a position within the optical beam path and a position outside of the optical beam path.