| 摘要 |
PROBLEM TO BE SOLVED: To provide a small-sized, compact, and inexpensive mechanism which suppress variation in the focal length of an fθlens, constituting the image formation optical system of the scanning device, with temperature. SOLUTION: The fθlens 6 constituting the image formation optical system of this device has 1st and 2nd lenses 61 and 62 and is held by arm members 11 and 12 and arm members 21 and 22 which are molded integrally and respectively toward the direction of the optical axis La while made movable in the reverse direction so that the lens interval (d) increases as the temperature rises and decreases as the temperature falls. The coefficient of linear expansion of a support board 15 where the arm members 11 and 12, and 21 and 22 are fixed is set to a value much less than that of the arm members 11 and 12, and 21 and 22. The lens interval (d) varies sensitively as the temperature varies to efficiently suppress variation in the focal length. The compact mechanism of simple constitution can be actualized with the arm members 11 and 12, and 21 and 22 molded integrally with the lenses 61 and 62.
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