| 摘要 |
The present invention discloses a large-field unit-magnification projection optical system. The optical system includes an optical axis, a spherical concave reflection mirror; a lens group with positive refracting power arranged adjacent the mirror with an air space therebetween. The lens group includes a first plano-convex lens, a negative meniscus lens adjacent the plano-convex lens, a positive lens adjacent the negative meniscus lens, a negative double-convex lens spaced apart far from the positive lens, and a second plano-convex lens. The optical system further includes a pair of prisms each having respective first and second surface. The second surfaces are arranged adjacent the flat surface of the plano-convex lens element on opposite sides of the optical axis and the first surfaces are arranged adjacent object planes and image planes, respectively. Each lens in the lens group and the pair of prisms provide chromatic aberration correction in a spectral region that contains at least g, h and i-line wavelengths. In this projection optical system, the object plane is parallel to the image plane.
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