Patent ID: 7508562

Claim:
A multi-beam scanning optical system configured to scan a plurality of laser beams on a scanned surface in a predetermined scanning direction, comprising: a light source that includes a plurality of laser emitters spaced from each other in the predetermined scanning direction, each of the plurality of laser emitters being configured to emit a laser beam; a diverging property changing element configured to change a diverging property of each of the laser beams emitted by the light source; a deflector configured to be sine-functionally oscillated and to deflect each of the laser beams with the diverging property thereof changed by the diverging property changing element so as to scan each of the laser beams on the scanned surface in the predetermined scanning direction; and a scanning speed controlling element configured to control a scanning speed at which each of the laser beams deflected by the deflector is scanned on the scanned surface, wherein the multi-beam scanning optical system is configured to satisfy a condition (1): Δ 1 ⁢ tan ⁡ ( W / 4 ⁢ K ⁢ ⁢ φ ) f < 0.01 ( 1 ) where Δ 1 represents a distance in the predetermined scanning direction between any two adjacent laser emitters of the light source, f represents a focal length of the diverging property changing element, W represents a scanning width of each of the laser beams on the scanned surface, K represents a scanning coefficient of the scanning speed controlling element, and φ represents an angular amplitude of the deflector.