Patent ID: 8345222

Claim:
A projection objective comprising: a plurality of optical elements arranged so that, during use of the projection objective, the plurality of optical elements images a pattern from an object field in an object surface of the projection objective to an image field in an image surface region of the projection objective at an image-side numerical aperture NA≧0.8 through a medium with refractive index n 1 in an image space adjacent to the image surface with electromagnetic radiation defining an operating wavelength λ, wherein, during use of the projection objective, the electromagnetic radiation forms a radiation beam including a plurality of rays incident on a plurality of optical surfaces with a plurality of respective angles of incidence, AOI, defining for each optical surface a maximum angle of incidence, AOI MAX , which is the maximum angle of incidence present on any one of the optical surfaces with the exception of an exit surface adjacent to the image surface, and wherein the condition NA/n 1 >k sin(AOI MAX ) holds for k≧1.