| 摘要 |
PROBLEM TO BE SOLVED: To constitute an optical system which is simple and does not interface with other optical elements as an optical system for guiding a light beam to a light beam detector by separating a scanning light beam, reflected by a return mirror, by a separation mirror, reflecting it again by the return mirror, and making the beam incident on the beam detector. SOLUTION: The light beam is guided to the light beam detector 63 in front of where an effective scan area on a scanned surface is scanned, and the arrival of the light beam is converted into an electric signal to obtain a synchronizing signal. Namely, the light beam which is deflected by a rotary polygon mirror is converged by a converged light beam in a horizontal scanning direction, returned by a 1st return mirror and a 2nd return mirror 92, and separated from its original optical path to the scanned surface by a separating mirror 64 provided right before a correcting lens; and then the light beam is passed through the 2nd return mirror 92 and converted by a light beam detection lens 65 into a light beam which is converted in the vertical scanning direction, so that the light beam is made incident on the light beam detector 63. |
