An illumination system of a microlithographic exposure apparatus comprises a condenser for transforming a pupil plane into a field plane. The condenser has a lens group that contains a plurality of consecutive lenses. These lenses are arranged such that a light bundle focused by the condenser on an on-axis field point converges within each lens of the lens group. At least one lens of the lens group has a concave surface. The illumination system may further comprise a field stop objective that at least partly corrects a residual pupil aberration of the condenser.