US Patent 7859732 Optical scanner and image forming apparatus

A scanning optical system is configured such that at least a smaller value of the size in a main scanning direction of optical beams entering into an opening provided in an aperture member relative to the size of the opening of the aperture member in the main scanning direction and the size in a sub scanning direction of the optical beams entering into the opening relative to the size of the opening in the sub scanning direction is equal to or larger than 1 and equal to or smaller than 2.