| 摘要 |
PROBLEM TO BE SOLVED: To simply manufacture an fθlens made of plastics by forming a scanning optical system in which the beam diameter on a photoreceptor drum is not affected by internal strain in the plastic lens. SOLUTION: This scanning optical device is composed of a polygon mirror 4 for deflecting a laser beam, a plastic fθlens 5 for forming an image in the main scanning direction and scanning at a constant speed and an image forming lens 6 in the sub-scanning direction. The plastic fθlens 5 for forming an image in the main scanning direction and scanning at a constant speed has no curvature in the sub-scanning direction and the cross-sectional shape of the image forming lend 6 in the sub-scanning direction is made to be an aspherical surface converging the laser beam in the sub-scanning direction.
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