Projection objective for a microlithographic projection exposure apparatus

A projection objective of a microlithographic projection exposure apparatus for imaging a mask on a photosensitive layer that is disposable in an image plane of the projection objective, wherein the projection objective is designed for immersion operation in which an immersion liquid adjoins the photosensitive layer, and wherein

• the immersion liquid forms an interface with a medium adjoins the immersion liquid on the object side of the projection objective, said interface being convexly curved towards the mask such that the maximum radius of curvature equals the product m·s, wherein s is the axial distance between the interface and the image plane and m is a real number between 20 and 120.