Light scanning unit and image forming apparatus employing the same

An image forming apparatus, comprising:

• a photosensitive body which forms an electrostatic latent image thereon;
• a light scanning unit including 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 the 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<Lmax−Lmin≦[20×(cos θ)5+10×λ/(5×10−4) where Lmax and Lmin 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;
• a developing unit which forms a toner image on the photosensitive body;
• a transfer unit which transfers the toner image formed on the photosensitive body to a printing medium;
• and
• a fusing unit which fuses the image transferred to the printing medium.