| 摘要 |
PURPOSE:To properly maintain the image-formation characteristics of the titled optical system and image-formation characteristics of a pupil by a method wherein an optical compensating device, with which the length of optical path will substantially be maintained even when the position between optical elements makes a change, is arranged in the optical path on a image-formation optical system. CONSTITUTION:The optical system is composed of an object plane 0, an image- formation plane I, an objective lens L10 and an image-formation lens L11. The relative position of said two lenses is to be changeable and the distance l of both lenses are also to be changeable. An optical path converter C consists of a mirror M5, moving mirrors M6 and M7, a fixed mirror M8 and a field stop D. Pertaining to the change DELTAl of the distance l, the mirrors M6 and M7 are moved as far as to DELTAl/2 to the direction shown by an arrow. At this time, as the length of optical path is extended as far as to DELTAl, the length of optical path is maintained constant in spite of the variation of interval l. |
