Patent ID: 6856439

Claim:
A tandem-type laser scanning apparatus comprising: a deflector for deflecting a first laser beam and a second laser beam in a main scanning direction by reflecting the laser beams simultaneously with a single surface, the first and second laser beams fulfilling the following conditions: |α|≠|β| α≠0 β≠0 where α represents an angle that a principal ray of the first laser beam makes with a main scanning plane when the first laser beam is incident on the deflector; and β represents an angle that a principal ray of the second laser beam makes with the main scanning plane when the second laser beam is incident on the deflector; and a scanning optical system for directing the deflected first and second laser beams to separate scanned surfaces corresponding thereto in such a way that the scanned surfaces are individually scanned with the laser beams focused thereon; wherein the scanning optical system includes: a common lens that has no curvature in a sub scanning direction and that transmits both the first and second laser beams; a first scanning lens that transmits, of the first and second laser beams transmitted through the common lens, the first laser beam but not the second laser beam; and a second scanning lens that transmits, of the first and second laser beams transmitted through the common lens, the second laser beam but not the first laser beam, the first and second scanning lenses each having a surface having a different twist from each other.