Patent ID: 6980344

Claim:
A scanning optical system comprising: a deflector having a reflection surface pivoting about a rotation axis, said reflection surface deflecting a light beam toward an object surface such that said light beam is scanned over the object surface in a main scanning direction; a mirror system arranged to reflect back said light beam deflected by said reflection surface so that said light beam travels toward the object surface after being deflected twice by said deflector, the mirror system reflecting back said light beam such that a projection of said light beam on an auxiliary scanning section is incident on said reflection surface for a first time at a first incident angle different from a second incident angle at which said projection of said light beam is incident on said reflection surface for a second time, said auxiliary scanning section being perpendicular to said main scanning direction; and a blocking member disposed between said deflector and the object surface, said blocking member preventing an unwanted light flux from striking the object surface, the unwanted light flux traveling from said deflector toward the object surface after being deflected by said deflector only once, wherein the difference between the first incident angle and the second incident angle provides separation between a path of the twice deflected light beam and a path of the once deflected unwanted light flux.