| 摘要 |
PROBLEM TO BE SOLVED: To provide a scanning optical system where the processing cost of the reflecting surfaces of a polygon mirror can be lowered. SOLUTION: The laser light emitted y a semiconductor laser 10 is collimated by a collimator lens 11 and then converged only in the vertical scanning direction by a cylindrical lens 11 to impinge on a reflecting surface 13a of the polygon mirror 13. The laser light reflected by the reflecting surface 13a is converged in the horizontal and vertical scanning directions by a scanning lens 14 to form a spot on the surface D of a photosensitive drum. The marginεof the reflecting surface 13a of the polygon mirror 13 is so determined that (1) 0.5[mm] < Rsin(π/N-W/(4f)cos(α/2)/(εcos(W/(4f))) < 1.0[mm]. Here N is the number of the reflecting surfaces of the polygon mirror, R is the circumscribing radium of the polygon mirror, (f) is the focal length of the scanning lens 14 in the horizontal scanning direction,αis the angle that the optical axis of the condenser lens 11 and the optical axis of the scanning lens 14 contain, and W is the scanning width on the photosensitive drum surface D.
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