Patent ID: 7719658

Claim:
An imaging system comprising: a projection objective that serves to project an image of a mask which can be set into position in an object plane onto a light-sensitive coating layer which can be set into position in an image plane; and a liquid-delivery device serving to fill immersion liquid into an interstitial space between the image plane and a last optical element on the image-plane side of the projection objective; wherein the last optical element on the image-plane side of the projection objective is arranged so that, seen in the direction of gravity, it follows the image plane; wherein the projection objective is configured in such a way that when the system is operating with immersion, the immersion liquid has at least in some areas a convex-curved surface facing in the direction away from the image plane; and wherein the imaging system is configured to be used in a microlithographic projection exposure apparatus, the image-plane-facing surface of the last optical element is shaped on the image-plane side at least substantially like a spherical shell, and the curvature radius of the image-plane-facing surface of the last optical element on the image-plane side is between 0.9 and 1.5 times as large as the axial distance between the last optical element on the image-plane side and the image plane.