Patent ID: 7042607

Claim:
A scanning optical system, comprising: a light source which emits a beam of light; a deflecting system that dynamically deflects the beam emitted by the light source with its deflecting surface; and a scan lens group including a molded resin lens, which focuses the beam dynamically deflected and scanned in a main scanning direction by the deflecting system on an image formation surface, wherein: the molded resin lens has a diffracting lens surface which is provided with a diffractive level difference structure formed on a base curve having refractive power; and a following condition is satisfied: 18< WL/P< 28 where “W” denotes an effective scan width (mm) on the image formation surface, “L” denotes a distance (mm) from the deflecting surface to the molded resin lens, and “P” denotes a distance (mm) from the deflecting surface to the image formation surface.