| 摘要 |
PROBLEM TO BE SOLVED: To provide a focusing method where an image of high quality can be obtained in focusing while the characteristics of a nonaxial optical system are sufficiently made the most of. SOLUTION: An imaging optical system TL comprises a plurality of optical surfaces and a stop ST, and has an eccentric reflecting surface S11 as at least one surface among a plurality of the optical surfaces. With the third prism P3 having the eccentric reflecting surface S11 as a focusing group, by the parallel transportation and rotary transportation of the focusing group, while almost fixedly retaining the imaging position on the axis and the incident angle of the main light on the axis on an image surface S13 to different conjugate distances, focusing for almost fixing the position of the whole of the image surface S13 is performed. COPYRIGHT: (C)2008,JPO&INPIT
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