US Patent 7639412 Optical scanning apparatus and image-forming apparatus

An optical scanning apparatus includes a light-source unit, an incident optical system for directing light beams emitted from the light-source unit to a deflecting unit, and an imaging optical system for guiding the light beams deflected from the deflecting unit to a surface to be scanned. The imaging optical system includes a toric lens whose power in the main scanning direction is different from that in the sub-scanning direction; the toric lens having the curvature centers of the meridians of a first toric surface connected to form a curved line located in a common plane Ha, and the curvature centers of the meridians of a second toric surface connected to form a curved line not located in a common plane.