A method of optimizing an imaging performance of a projection exposure system is provided, wherein the projection exposure system comprises an illumination optical system for illuminating a patterning structure and a projection optical system for imaging a region of the illuminated patterning structure onto a corresponding field. The method comprises setting the field to a first exposure field, setting optical parameters of the projection exposure system to a first setting such that the imaging performance within the first exposure field is a first optimum performance, changing the field to a second exposure field, and changing the optical parameters to a second setting such that the imaging performance within the second exposure field is a second optimum performance.