| 摘要 |
PROBLEM TO BE SOLVED: To reduce jitter by reducing the variation of the beam size of a light beam made incident on a synchronization detector by a simple constitution. SOLUTION: The variation of the beam size of the light beam made incident on the synchronization detector 36 is caused by the fluctuation of the accuracy of the reflection surface of a light deflector and environmental temperature, so that the output balance of the synchronization detector 36 is varied. Then, a slit 42 is provided between a scanning lens and the synchronization detector 36, and the opening of the light beam made incident on the synchronization detector 36 is limited, so that the F number of the light beam is made large. Thus, the depth of focus of the light beam made incident is increased, and the variation of the beam size for each scanning line is reduced and the output balance of the synchronization detector 36 is maintained, so that the jitter in which the writing position of each scanning line is varied is reduced.
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