| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system that is capable of imaging a wide observation view angle on an imaging element by a simple configuration and is small and inexpensive, and to provide an endoscope using the same. SOLUTION: 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 an 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 transparent 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 as a whole on the image surface 5 without formation of an intermediate image in the first optical path A such that an object point around the central axis 2 is formed opposite intersecting the central axis 2 one time near the opening S. At least one of the reflecting faces of the back group Gb is composed of a rotation-symmetrical face that is discontinuous on the central axis. COPYRIGHT: (C)2009,JPO&INPIT
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