1. An imaging optical system, comprising: a plurality of mirrors configured to an object field in an object plane into an image field in an image plane, wherein: the imaging optical system has an image-side numerical aperture of at least 0.3; the imaging optical system has a pupil obscuration which is greater than 0.40; the imaging optical system has an image field size of at least 1 mm×10 mm; and the imaging optical system is an EUV projection lithography imaging optical system.