US Patent 7385181 Optical scanning device and image forming device

Light beams emitted from a plurality of light source devices are deflected by a shared light deflector. The light beams are respectively concentrated on different scanning subjects using a first scanning lens and second scanning lenses and are used to perform a scan. All light beams make an angle in a sub-scanning direction to a normal line of a reflecting surface of the light deflector. An incidence surface of the first scanning lens is a surface of which a curvature in the sub-scanning direction changes depending on a main scanning direction. The incidence surface of the first scanning lens is also an optical surface of which a negative refracting power becomes stronger toward a periphery of the surface in the main scanning direction.