Patent ID: 8305413

Claim:
An optical scanner unit comprising: a light source; a deflector which deflects a light beam from the light source; an optical scan system which includes an fθ lens and focuses the light beam deflected by the deflector on an image support member to form an electrostatic latent image; and a synchronous detector which receives a part of the light beam deflected by the deflector and detects a write start position on the image support member in a main scan direction, wherein a light beam receiving face of the synchronous detector is shifted from an orientation that is normal to a direction of the part of the light beam received by the synchronous detector by predetermined non-zero angles θ 2 and θ 3 in planes generally aligned with the main and sub scan directions, respectively, of the optical scanner unit, wherein a second straight line connecting an exit point of an optical axis from the fθ lens to be incident on the synchronous detector in the main scan direction and a light receiving point of the synchronous detector, θ 2 is an angle between the second straight line and a normal line of the synchronous detector, where θ 3 is an angle between a third straight line connecting an exit point of the light beam from the fθ lens to be incident on the synchronous detector in the sub scan direction and a light receiving point of the synchronous detector and a normal line of the synchronous detector and the angle θ 3 is determined to satisfy the following condition (2): θ2>θ3.