An optical
system for a projection
exposure apparatus has an illumination optical unit for guiding illumination and imaging light (3) from a
light source to an
object field in which an object to be imaged can be arranged, and an imaging optical unit for imaging the
object field to an
image field in which a substrate to be exposed can be arranged. The imaging optical unit has an
exit pupil (36) with at least one obscured
exit pupil region (38) located in an outer
pupil edge (37). The illumination optical unit is designed in such a way that an
illumination angle distribution occurs when the
object field is illuminated with the illumination and imaging light (3) and can be described by means of an illumination
pupil (12a), the illumination
pupil region (I) illuminated by the illumination light being adapted to a shielded
exit pupil region (38) of the imaging optical unit. A shielded exit pupil region (38) of the imaging optical unit may have a non-central geometric
center of mass (SP). In a variation of the optical
system, the illumination optical unit is embodied such that an
illumination angle distribution occurs in the object field and can be described by an illumination pupil (12a) having an obscured illumination pupil region (31), the envelope of which deviates from a circle in pupil coordinates (sigma x, sigma y) normalized with respect to an outer pupil edge (37) and / or in absolute pupil coordinates (rhox, rhoy). In order to specify the illumination pupil (12a), the diffractive behavior of at least one
object structure of the object to be imaged is analyzed, the position of the occluded exit pupil region (38) in the exit pupil (36) is detected, and the illumination pupil (12a) is adjusted such that at least one variation of the optical
system occurs. This improves the resolution of the optical system.