| 摘要 |
PURPOSE:To excellently compensate the image plane performance by providing a lens which is arranged between a deflector and a spherical mirror and has a difference between the center of radius of curvature of an incidence surface and the center of the radius of curvature of a projection surface in a scanning plane, and satisfying specific conditional inequalities. CONSTITUTION:The inequalities preferably hold for the relation among the distance (object point) (s) (not shown in figure) from the deflection point 10a to the position where a collimator lens converges a beam in the absence of a toric lens 15 and the spherical mirror 20, the radius (R1a) of curvature of the spherical mirror 20, and the radius (RM) of curvature of the lens projection surface in the main scanning direction, the relation between the distance (d) from the deflection point 10a of the polygon mirror 10 to the mirror 20 and the radius (RM) of curvature, and the relation between the core thickness (d1) of the toric lens 15 and the radius (R2a) of curvature of the lens incidence surface in the main scanning direction. When the inequalities are satisfied, an excellent distortion characteristic and excellent image plane flatness are obtained over a wide view angle range. |
