| 摘要 |
Laser beams emitted from a plurality of light emitting points of a light source unit are converged by a first optical system to be focused in an auxiliary scanning direction in the vicinity of a reflecting surface of a polygon mirror, dynamically deflected by the polygon mirror, and converged by a second optical system to form scan lines on a scan target surface. The first optical system includes a plurality of cylindrical lenses, in which a second cylindrical lens is attached to a holder so as to be movable in the optical axis direction and is selectively stopped at two positions that satisfy a particular relationship. By the composition, the interval between the scan lines on the scan target surface measured in the auxiliary scanning direction can be switched correctly and with extreme ease in the multibeam optical system, without the need of using a movement control mechanism composed of high precision parts.
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