1. A method for adjusting a projection objective of a projection exposure machine of the type used for microlithography in the fabrication of semiconductor components and having an illumination device for providing an illumination beam and a plurality of optical elements in the path of the illumination beam for projecting an image onto a substrate, at least some of the optical elements being capable of being adjusted for altering aberrations of the projection objective, said method comprising the steps of: (a) establishing an initial polarization of the illumination device; (b) adjusting the projection objective with respect to at least one of the aberrations under initial polarization; (c) changing the polarization of the illumination device from said initial polarization to a different polarization; and (d) adjusting the projection objective with respect to said at least one aberration based on said different polarization.