| 摘要 |
PURPOSE:To set optionally intervals of a beam on an image carrier in a subscanning direction and to facilitate synchronization with a beam detection signal by providing a means which makes plural beams into parallel light and a prism which vary beam intervals of the parallel light optically. CONSTITUTION:Divergent light from a semiconductor laser array 11 as a light source is made into parallel beams L1-L4 by a collimator lens 12 and those parallel beams are incident on the prism 17. The prism 17 is a triangular prism, the incidence surface 171 and projection surface 172 for the beams slant to each other, and the beams diffracted by the incidence surface 171 travel straight in the prism as they are and are refracted again by the projection surface 172. Further, the angle of incidence of the parallel beams is varied to vary parallel beam intervals Pe at the time of incidence to intervals Ps of projection beams B1-B4 at the time of projection. Thus, the angle of incidence on the prism 17 is selected properly to vary the intervals Ps of the projection beams.
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