A method for improving imaging properties of two or more optical elements comprises the step of determining for at least one of the two optical elements a polarisation-dependent perturbation. In a further step a polarisation-independent perturbation is determined for at least one of the two optical elements. Then a target position for the at least one movable optical element is calculated such that, in the target position, the total perturbation of the at least two optical elements which is made up of the polarisation-dependent perturbations and polarisation-independent perturbations of the two optical elements, is minimized. Finally the at least one movable optical element is moved the to the calculated target position.