| 摘要 |
PROBLEM TO BE SOLVED: To perfectly prevent scattered light, stray light and ghost light by providing a shield plate which pass a light beam through only when a scan light beam exists on a prescribed area of a surface to be scanned in the vicinity of an image forming point of an optical path from a first rotary reflection surface to a second rotary reflection surface. SOLUTION: The light beam polarized by the first reflection is made incident on a first transmission lens 31 of a transmission optical system, and becomes a convergent beam to be image formed on the image forming point P. The light beam image formed once on the image forming point P becomes a divergent beam next, and changes the direction by a first turning mirror 41 to be incident on a second transmission lens 32. An afocal optical system is used for a transmission optical system from the first reflection surface to the second reflection surface, and the shield plates 71, 72 are placed in the vicinity of the image forming point P between the first transmission lens 31 and the second transmission lens 32. The device is constituted so that the light beam passes through the shield plates 71, 72 only when the beam exists in the range to be scanned, from a reference position detector 81 to a terminal end of an effective scan area. |
