| 摘要 |
PROBLEM TO BE SOLVED: To detect a synchronizing signal of the optical scanner able to detect a synchronizing signal with high accuracy. SOLUTION: An optical scanner is made up of a light source section provided with a laser light source, a rotary polygon mirror, an fθlens, a photosensing drum and a synchronizing signal generating circuit or the like. The synchronizing signal generating circuit is made up of a photo diode 6 and a signal processing circuit processing an output signal from the photo diode 6. Then a width L of an effective light receiving area of the photo diode 6 in the main scanning direction is selected to satisfy an equation of L<=2W, where W is a diameter of a laser beam 21 in the main scanning direction.
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