| 摘要 |
PURPOSE:To compensate the slanting of the reflecting surface of a deflecting mirror, by using a return mirror which has the 1st focal point on the reflecting surface of the deflecting mirror and the 2nd focal point at a fine spot scanning point on the surface of a photoreceptor. CONSTITUTION:Coordinate axes (x) and (y) are set on the basis of an origin 0 and the reflecting surface determined by an elliptical locus 7 which has focal points F and F' and a long and a short radus (a) and (b) is formed. Then, a light beam from the focal point F is reflected by the reflecting surface and focused on the other focal point F', so the reflection point of a rotary polygon mirror 2 is set at one focal point of the ellipitcal locus 7 and the scanning surface of a photosensitive drum 4 is positioned at the other focal point F'. The return mirror 8 having a curved reflecting surface conforming with the elliptical locus 7 is arranged in an area in the elliptical locus 7 which is necessary as the reflecting surface to form an optical path F-M-F', and an F-theta lens 3 is arranged on the optical path. The optical path length from the F to the F' becomes equal, so curvature of field is eliminated. |
