Patent ID: 7019768

Claim:
A scanning optical system for dynamically deflecting a laser beam emitted from a light source by a deflecting system, converging the dynamically deflected laser beam by an imaging optical system into a spot beam on a scan target surface, and thereby scanning the spot beam in a main scanning direction on the scan target surface, comprising: a collimator lens being placed on an optical path between said light source and said deflecting system, wherein at least one of a front surface and a rear surface of said collimator lens including: a central area through which part of the laser beam in the vicinity of a central axis of the laser beam passes; at least one first outer area through which part of the laser beam outside the laser beam incident on said central area passes, said at least one first outer area having an effect on the laser beam so that the laser beam after passing through said at least one first outer area is given a first phase difference with respect to the laser beam passing through said central area, the first phase difference not including a phase difference of zero; and at least one second outer area through which part of the laser beam other than the laser beam incident on said central area and said at least one first outer area passes, said at least one second outer area having an effect on the laser beam so that the laser beam after passing through said at least one second outer area is given a second phase difference with respect to the laser beam passing through said central area, the second phase difference being different from the first phase difference and including a phase difference of zero.