| 摘要 |
PROBLEM TO BE SOLVED: To reduce the fluctuation of a spot diameter caused by the fluctuation of temperature and the fluctuation of interval between scanning lines in the case of multibeam scanning by positively utilizing the unevenness of temperature in the housing of an optical scanner. SOLUTION: This optical scanner is provided with a 1st optical system for coupling divergent luminous flux from a light source, a 2nd optical system by which the coupled luminous flux is formed into an image as a line image long in a main scanning direction on the deflection and reflection surface of a light deflector, and a 3rd optical system by which the luminous flux deflected by the light deflector 4 is condensed as a light spot on a surface to be scanned. The 3rd optical system 6 is provided with one or more resin lenses 6a and 6b having positive power in the main scanning direction and/or a subscanning direction, and the 2nd optical system 3 has a resin lens 3a having negative power so as to reduce the fluctuation of power of the 3rd optical system caused by temperature change. The optical scanner is provided with temperature distribution forming means 1 and 4 forming temperature distribution so that the temperature change of an atmosphere in the vicinity of the 1st optical system:ΔT1, the temperature change of an atmosphere in the vicinity of the 2nd optical system:ΔT2, and the temperature change of an atmosphere in the vicinity of the 3rd optical system:ΔT3 satisfy a condition:ΔT1>ΔT3 and/orΔT2>ΔT3 inside housing.
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