| 摘要 |
A multi-beam laser exposure unit includes a light beam deflector for deflecting light beam in a predetermined direction, a plurality of laser devices, a pre-deflection optical system, including a glass lens and a plastic lens, for converting a cross sectional shape of light beam emitted from the respective laser devices to a predetermined shape, and a post-deflection optical system, including three lenses for image-forming each light beam deflected by the deflector to be scanned on a predetermined image surface at a uniform speed. Power of three lenses of the post-deflection optical system is defined to be positive, negative, positive in order in a direction parallel to a rotational axis of each of reflective surfaces of the deflector from the side close to the deflector. Also, the power of three lenses of the post-deflection optical system is defined to be positive, negative, positive in order in a direction perpendicular to the rotational axis. Thereby, an effective deflection angle can be enlarged and a registration error can be reduced.
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