Imaging systems, in particular a projection objectives of a microlithographic projection exposure apparatus, are provided. The imaging systems can have an optical axis and produce an image field which is extra-axial relative to the optical axis. The imaging systems can include a first optical element which causes a first distribution of the retardation in a plane that lies perpendicular to the optical axis, and at least one second optical element which causes a second distribution of the retardation in a plane that lies perpendicular to the optical axis. The second distribution of the retardation can at least partially compensate the first distribution of the retardation. The first and the second optical elements can be designed without rotational symmetry relative to the optical axis.