Abstract: An illumination system for a microlithographic projection exposure apparatus comprises a masking device and a masking objective which projects the masking device onto an image plane. The illumination system further includes an optical correction element having a surface that is either aspherically shaped or supports diffractive structures that have at least substantially the effect of an aspherical surface. This surface is arranged at least approximately in a field plane which precedes the image plane of the masking objective The aspherically acting surface is designed such that a principal ray distribution generated by the illumination system in the image plane matches a principal ray distribution required by a projection objective.