Patent ID: 8189027

Claim:
An exposure unit for exposing a plurality of photoconductive drums having rotary axes thereof arranged parallel to each other on a single plane by a plurality of light beams emitted from a plurality of light sources, each of said plurality of photoconductive drums having a surface to be exposed when forming an electrostatic latent image thereon, said exposure unit comprising: one or a plurality of polygon mirrors each having a plurality of reflection surfaces, said one or the plurality of polygon mirrors being configured to rotate about a common rotary axis, wherein each of the plurality of light beams emitted from the plurality of light sources is deflected by said one or a corresponding one of the plurality of polygon mirrors and scans the surface of a corresponding one of the plurality of photoconductive drums, wherein at least one of a light emission period and a light emission amount of each of the plurality of light beams emitted from the plurality of light sources is controlled depending on an image height of the electrostatic latent image formed on the surface of each of the plurality of photoconductive drums, and the common rotary axis of said one of the plurality of polygon mirrors is separated from the rotary axes of the plurality of photoconductive drums by identical distances along respective normals which are perpendicular to both the common rotary axis and a corresponding one of the plurality of rotary axes.