US Patent 7271823 Optical scanner and image forming apparatus

An optical scanner has a deflector, a coupling lens, a cylindrical lens, a plate through which light to and from the deflector pass, and an optical system which condenses the light deflected on a surface to be scanned. Bundles of light beams incident on the deflector have an angle between the bundles in a rotating plane of the deflector, and expressions 0.6<(θ1max−α)/(θ2+α)<1.4, and 0.6<(θ1min−α)/(θ2+α)<1.4, are satisfied, where θ1max and θ1min are maximum and minimum average angles of incidence on the deflecting surface, θ2 is a half-view angle, and α is an angle of inclination of the plate in the rotating plane with respect to a main scanning direction.