| 摘要 |
A post-objective type optical deflector, in which luminous fluxes are condensed by a convergent lens and thereafter deflected by a polygonal mirror, among apparatuses for scanning a laser beam, involves a problem in the deterioration of the curvature of field and the f theta characteristic. The deterioration of the curvature of field and the f theta characteristic may be corrected by forming a reflecting surface of a polygonal mirror into a convex surface or a convex cylindrical surface and adequately selecting the relationship between the distance A from the rotational center to the center of the reflecting surface, the radius of curvature R of the reflecting surface, the distance Lo from the deflection point of the polygonal mirror to the scanning surface, and the scanning width Yo.
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