An illumination system of a micro-lithographic projection exposure apparatus is provided, which is configured to illuminate a mask positioned in a mask plane. The system includes a pupil shaping optical subsystem and illuminator optics that illuminate a beam deflecting component. For determining a property of the beam deflecting component, an intensity distribution in a system pupil surface of the illumination system is determined. Then the property of the beam deflecting component is determined such that the intensity distribution produced by the pupil shaping subsystem in the system pupil surface approximates the intensity distribution determined before. At least one of the following aberrations are taken into account in this determination: (i) an aberration produced by the illuminator optics; (ii) an aberration produced by the pupil shaping optical subsystem; (iii) an aberration produced by an optical element arranged between the system pupil surface and the mask plane.