| 摘要 |
PROBLEM TO BE SOLVED: To reduce defocusing and pitch deviation on a scanned surface by using an fθlens composed of a single lens. SOLUTION: A collimator lens 12, a stop 13, a cylindrical lens 14, and an optical deflector 15 are arranged in the projection direction of a light source 11 and an fθlens 16 as an image formation optical system having fθcharacteristics and the scanned surface 17 of a photoreceptor drum, etc., are provided in the deflection direction of the optical deflector 15. The fθlens 16 is fixed on a PC-made holding member 21 which has a large coefficient of linear expansion and the holding member 21 is fixed to an optical box 22 as a support member for the light source 11, collimator lens 12, etc., nearby the deflector 15. The optical box 22 is molded out of a glassfiber containing material and is much less in coefficient of linear expansion than the holding member 21. As the temperature of the device rises, the holding member 21 expands and then the fθlens 16 which is arranged thereupon moves, so that the defocusing in a vertical scanning direction is corrected until no practical problem is left.
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