Patent ID: 7136208

Claim:
A light scanning apparatus comprising: an incidence optical system for guiding a light beam emitted from a light source means to a deflection means; and an imaging optical system for guiding the light beam reflected on the deflection means on a surface to be scanned, which has at least one diffracting surface having a power in a sub-scanning section; wherein the deflecting surface of the deflection means and the surface to be scanned are conjugated with each other; wherein in the sub-scanning section, a principal ray of the light beam reflected by the deflection means passes through an outside of an optical axis of the diffracting surface; and wherein, letting β be a transversal magnification ratio of the imaging optical system in the sub-scanning section, f [mm] be a focal length of the imaging optical system in the sub-scanning section, δf [mm] be an amount of variance of the focal length of the imaging optical system in the sub-scanning section when a wavelength of the light beam emitted from the light source means is varied by 1 nm, h [mm] be a distance between the principal ray and the optical axis of the diffracting surface in the sub-scanning section on the diffracting surface, and R [dot/inch] be a resolution, a following condition is satisfied: |(1−β)·(δ f/f )· h|<{ 25.4/ R}/ 2, |h|>0.