US Patent 7728863 Optical scanning device and image forming apparatus

An optical scanning device has a light source, a unit configured to deflect a light beam from the light source; and a system including at least two scanning lenses and configured to guide the light beam deflected to a surface to be scanned. One of the scanning lenses closest to the deflecting unit has a positive refractive power in a main scanning direction and zero or approximately zero refractive power in a sub scanning direction, and another one of the scanning lenses closest to the surface has a negative refractive power in the main scanning direction, a positive refractive power in the sub scanning direction, and an incidence surface in the sub-scanning direction which is convex toward the deflecting unit.