| 摘要 |
PROBLEM TO BE SOLVED: To vary an optical path length in an image-forming optical system and to easily control focusing. SOLUTION: Bellows 13 which can be extended/contracted in an axial direction forming a water tight space are provided between two transparent glass plates 11 and 12 which are oppositely arranged. Optical refraction liquid 16 is filled in the water tight space. The two glass plates 11 and 12 are relatively moved in parallel by a driving mechanism constituted of a yoke 19, coils 20 and 21 and a permanent magnet 22. The length (thickness) of the optical axis direction of optical refraction liquid 16 is changed by extending/contracting the bellows 13 and moving the two glass plates 11 and 12 in parallel. When an automatic focus mechanism is constituted by using the optical path variable element, the mechanism for driving the lens of the image-forming optical system is not required and the automatic focus mechanism of simple constitution can inexpensively be constituted. |
