| 摘要 |
PURPOSE:To correct uneven scanning pitches due to the face inclination of a rotary polygon mirror in a scanning optical system having >=30 deg. maximum scanning angle (picture angle) by arranging an axially symmetrical aspherical lens and a cylindrical mirror having refractive force in a sub-scanning direction between the rotary polygon mirror and an image face. CONSTITUTION:A cylindrical lens 2 having refractive force in the direction vertical to a scanning direction for linearly forming the image of a laser beam 1 projected from a light source, a light deflector 3 having its deflecting reflection face in the vicinity of the linear image based upon the lens 2, the axially symmetrical aspherical lens 4 between the light deflector 3 and a photosensitive drum 6, and the cylindrical mirror 5 having refractive power in the direction vertical to the scanning direction are arranged. The lens 4 is a meniscus lens having a convex face on the image face, and when r1 is the radius of curvature of the 1st face, r2 is the radius of curvature of the 2nd face, d1 is center thickness, and (f) is a focal distance, 1<=r1/r2<1.5 and d1/f>0.08 are satisfied. Consequently, uneven scanning pitches due to the differences of inclined angles on respective faces of the rotary polygon mirror can be corrected. |
