| 摘要 |
PROBLEM TO BE SOLVED: To improve the rigidity and dustproof property of an optical box and to prevent its optical performance from being deteriorated by the vibration of a lens by providing the optical box with a first rib surrounding the periphery of the lower part of the lens, covering the lower part of the lens and preventing dust and a second rib along the outside of the first rib. SOLUTION: The first rib 20a is provided on the optical box along a lower end periphery of an fθlens, and further, the second rib 20b is provided on the outside of the first rib 20a, and the intrusion of the dust is prevented further by these ribs 20a, 20b. A beam L scanned by a polygon mirror 24 is converged by the lens, and since a plane tilt shown by beams L', L" caused by the polygon mirror 24 are corrected, and since its width X is reduced to the width X' on the position of the second rib 20b of the outside, the height of the second rib 20b is heightened to h2. Thus, the dust D hardly become close to the fθlens, and the intrusion of the dust D is reduced.
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