| 摘要 |
PROBLEM TO BE SOLVED: To improve the level of printing quality by reducing the interval error of the sub-scanning direction of the scanning line ascribed to the angle difference of the polarizing angle of the light emitting part in a multi-beam scanning optical system which has a birefringent optical element in the scanning optical means. SOLUTION: The scanning optical means has at least one scanning optical element made of resin. In the resin-made scanning optical device, the direction of the birefringence principal axis of one end of the resin-made scanning optical device and the direction of the birefringence principal axis of the other end of the resin-made scanning optical device are different due to stress distribution produced at the time of cooling during forming toward the main scanning direction around the optical axis, the interval of the adjoining scanning lines among the scanning lines which a plurality of luminous fluxes focused on the surface to be scanned draw on the surface to be scanned is displaced toward the main scanning direction in the effective scanning region, and the polarizing angles of the luminous fluxes respectively emitted from a plurality of light emitting parts differ mutually. The scanning optical means has at least one setting means to set the interval error of the sub-scanning direction of the scanning line caused by these phenomena to 1/5 or smaller of the desired scanning line interval.
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