| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact and inexpensive optical system capable of imaging at a wide observation viewing angle on an imaging device with simple constitution, and an endoscope using the same. SOLUTION: The optical system comprises a front group Gf including at least one reflecting surface, a back group Gb, and an opening S disposed between the front group Gf and the back group Gb. At least one surface of a back group first reflecting surface 22 and a back group second reflecting surface 23 is formed by a continuous curved surface on a central axis. Light flux which enters a back group transparent medium Lb forms an approximately Z-shaped first optical path A by, in the order of forward ray tracing, passing through the opening S, entering the back group transparent medium Lb via a back group first transmitting surface 21, being reflected to the side opposite to an image surface 5 by the back group first reflecting surface 22, being reflected to the image surface 5 side by the back group second reflecting surface 23, and going out from the back group transparent medium Lb to the image surface 5 side via a back group second transmitting surface 24. The first optical path A at least between the back group first reflecting surface 22 and the back group second reflecting surface 23 is formed on only one side with respect to the central axis 2, and an image is formed in an annular shape on the image surface 5 without formation of an intermediate image in the first optical path A. COPYRIGHT: (C)2009,JPO&INPIT
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