| 摘要 |
In a scanning optical system, a partial light blocking member having an annular light blocking part (for blocking off part of the incident laser beam entering the annular area around the central axis of the laser beam) is placed on an optical path between the laser light source and the polygon mirror. The scanning optical system including such a partial light blocking member is installed in a printer. By the effect of the partial light blocking member, the intensity of side lobes (several rings of light accompanying the main beam) is prevented from exceeding a threshold value even when optical surfaces of an imaging optical system of the scanning optical system have certain microscopic undulations, by which black stripes occurring in halftone printing can be eliminated.
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