Patent ID: 7408689

Claim:
A light scanning unit usable with an image forming apparatus, comprising: a light source which emits light beam with a predetermined wavelength; a beam deflector which deflects and scans the light beam emitted by the light source toward a photosensitive body; and an f-θ lens which has at least one plastic lens and forms an image corresponding to the light deflected by the beam deflector on the photosensitive body, the light scanning unit satisfying a following formula 0<L max −L min ≦[20×(cos θ) 5 +10]×λ/(5×10 −4 ) where L max and L min respectively represent a maximum value and a minimum value of a total light passing distance from a light axis of at least one plastic lens according to a deflection angle, θ is an angle formed between a polarization direction of the light beam emitted by the light source and a sub-scanning direction, and λ is a wavelength of the light beam emitted by the light source.