Imaging optical system and projection exposure installation for microlithography including same

An imaging optical system, comprising:

• a plurality of mirrors configured to image an object field in an object plane into an image field in an image plane, the plurality of mirrors comprising precisely eight mirrors, wherein the imaging optical system has a pupil obscuration of greater than 0% and less than 10%, and a product of a working spacing of the penultimate mirror and an image side numerical aperture of the imaging optical system is at least 10 mm, wherein:
• the plurality of mirrors are configured to image the object field in the object plane into the image field in the image plane via a path of light from the object field to the image field;
• the precisely eight mirrors include a last mirror along the path of the light and a penultimate mirror along the path of the light;
• a main plane extends centrally through the image field;
• the main plane is perpendicular to the image field;
• and
• the penultimate mirror is on only one side of the main plane.