| 摘要 |
An imaging optical system includes a set of mirrors including at least three mirrors on a beam path. Only a last mirror on the beam path has a positive optical power and all other mirrors have negative optical power. The sum of the optical powers of the mirrors is zero. An external posterior aperture stop is on the beam path between the last mirror and the image plane. A back focal length of the optical system is equal to or greater than an effective focal length of the optical system. The field of view is large, and typically at least 30-40 degrees in one plane.
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