| 摘要 |
PURPOSE:To obtain a laser scanner with small curvature of field in a scanning vertical direction and high resolution by comprising a scanning lens (Ftheta lens) of one lens, and forming at least one lens surface in specific shape. CONSTITUTION:A beam 91 emitted from a laser beam source 22 is changed to almost parallel rays via a collimator lens 12. A cylindrical lens 1 is arranged so as to function only in the scanning vertical direction, and the beam is converged in the scanning vertical direction in the neighborhood of the reflecting surface 33 of a rotary polygonal mirror 3. As for the scanning vertical direction, geometric conjugate relation exists between the neighborhood of the reflecting surface 33 and a photosensitive drum plane 6. The scanning lens (Ftheta lens) 4 is comprised of one lens. The surface of the lens near to the rotary polygonal mirror 3 is formed in spherical shape. The surface separated far from the rotary polygonal mirror 3 is comprised of a lens surface in asymmetric shape for an optical axis whose curvature in the scanning vertical direction is changed successively along the scanning direction corresponding to the rotating position of the rotary polygonal mirror 3. |
