| 摘要 |
PURPOSE:To prevent a ghost image due to reflected light beams from the surface of a filter from being formed by allowing a light shielding means to cut off light beams which is reflected by the filter surface and further reflected by a mirror surface which adjoins to a mirror surface where a scan is made currently. CONSTITUTION:When part of beams L2 scanned by a mirror surface 21 of a polygon mirror 2 is reflected by the surface of the filter 5 to travel backward in an image forming lens 3 and then reflected by a mirror surface 22 which adjoins to said mirror surface 21, a light shield plate 8 should be provided on the optical path of the reflected light beams L4 traveling to the image forming lens 3 again. The light shield plate 8 is therefore installed at the end part of the image forming lens 3 on the opposite side from the incidence side of the beams L1 incident on the polygon mirror 2 from a beam source 1 about an optical axis X and near by the image forming lens surface facing the polygon mirror 2 at specific distance from the optical axis X. |
