| 摘要 |
PURPOSE:To form an SOS optical path to a smaller size by reflecting a laser beam, which is reflected by mirrors for turning back images, by a mirror to be exclusively used for a sensor, then reflecting the beam at least once by the mirrors for turning back images and guiding such beam to the SOS sensor. CONSTITUTION:At least a piece of the mirrors 14, 15 for turning back images are provided between a deflector and recording medium and the sensor (SOS sensor) 20 for detecting an image drawing position is installed in the equiv. position of the recording medium; in addition, the mirror 21 to be exclusively used for guiding the laser beam to this sensor 20 is provided. The incident laser beam on the SOS sensor 20 is, therefore, reflected by the mirror 21 after reflection by the mirrors 14, 15 and thereafter, the laser is reflected at least once by the mirrors 14, 15 and enters the sensor 20. The optical path to the sensor 20 is thereby constituted to the smaller size by effectively using the mirrors 14, 15 and the mirror 21 even if the distance from the deflector to the recording medium is increased by an increase in main scanning width. The sensor 20 is thus installable to the equiv. position of the recording medium and the constitution of the optical device to a single unit is not impaired.
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