| 摘要 |
<p>An imaging optical system (7) comprises a plurality of mirrors (Ml to M8), which image an object field (4) in an object plane (5) into an image field (8) in an image plane (9). At least one of the mirrors (M6, M7, M8) is obscured, and thus has a through-opening (21) for imaging light (15) to pass through. The fourth-last mirror (M5) in the light path before the image field (8) is not obscured and provides, with an outer edge (22) of the optically effective reflection surface thereof, a central shadowing in a pupil plane (17) of the imaging optical system (7). The distance between the fourth-last mirror (M5) and the last mirror (M8) is at least 10 % of the distance between the object field (4) and the image field (8). An intermediate image plane (23), which is closest to the image plane (9), is arranged between the last mirror (M8) and the image plane (9). The imaging optical system (7) has a numerical aperture of 0.9. These measures, not all of which must be effected simultaneously, lead to an imaging optical system with improved imaging properties and/or reduced production costs.</p> |
