| 摘要 |
PURPOSE:To correct the curvature of image and the ftheta characteristic at a high level by combining a polygon optical deflector in which the reflecting surface for reflecting light beams from a light source have been formed by a convex hyperbolic surface or hyperbolic cylindrical surface, and a pseudo cylindrical lens. CONSTITUTION:The optical deflector is formed by a polygon optical deflector 1 and a pseudo cylindrical lens 3 provided in the vicinity of a scanning surface 2. The polygon optical deflector 1 rotates centering around the O point and when (x) and (y) coordinates are taken as shown in the figure, a reflecting surface 4 having six surfaces by a hyperbolic surface or a hyperbolic cylindrical surface given by the expression is formed. Also, the pseudo cylindrical lens 3 is formed by a usual cylindrical surface 5 and a higher order curved surface 6 of a2X<2>+a4X<4>. An axial light beam 7 and a differential light beam 8 are made incident so as to be converged to S0 being in a position of l from the center O of the polygon optical deflector 1, reflected by the reflecting surface 4 and pass through the pseudo cylindrical lens 3, and form an image in a S point. In such a way, the curvature of image and the ftheta characteristic are corrected at a high level. |
