A magnifying imaging optical system is disclosed that has precisely three mirrors, which image an object field in an object plane into an image field in an image plane. A ratio between a transverse dimension of the image field and a transverse dimension measured in the same direction of a useful face of the last mirror before the image field is greater than 3. In a further aspect, the magnifying imaging optical system is disclosed that has at least three mirrors, which image an object field in an object plane in an image field in an image plane. A first mirror in the beam path after the object field is concave, a second mirror is also concave and a third mirror is convex. An angle of incidence of imaging beams on the last mirror before the image field is less than 15°.