| 摘要 |
PROBLEM TO BE SOLVED: To provide a scanning optical system capable of realizing higher-speed printing while realizing higher-definition printing. SOLUTION: After laser beams emitted from a semiconductor laser 10 are made parallel beams by a collimating lens 11, they are focused only in a subscanning direction (the direction parallel to the rotation direction of a polygon mirror) by a cylindrical lens 12 and made incident on the reflection surface 13a of the polygon mirror 13. The laser beams reflected by the reflection surface 13a are respectively converged in a main scanning direction and in the subscanning direction by a scanning lens 14 so as to form a spot on the surface D of a photoreceptor drum. The surface number N and the circumradius R of the reflection surface 13a of the mirror 13 are decided so as to satisfy a following condition (1). (1) 0.7×10<-3> f<2Rϕsin (π/N-W/(4f))cos(α/2)<1.2×10<-3> f Provided that f means the focal distance of the lens 14 in the main scanning direction,αmeans an angle formed by the optical axis of a collimating lens 11 with the optical axis of the lens 14, W means scanning width on the surface D of the photoreceptor drum andϕmeans a spot diameter on the surface D of the photoreceptor drum.
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