PURPOSE: To correct even a position shift of scanning lines in the scanning direction in a partial scanning area, and to prevent the deterioration in print quality by specifying the angle of incidence of light to N pieces of mirror surfaces in photoscanning to satisfy a basic expression.
CONSTITUTION: A photoscanning start signal S1 and a reference mirror surface detection signal S2 are inputted to a counter 30. An ROM31 is stored with a value corresponding to θj=θo+2j for every mirror surface of a revolving polygon mirror (where θj is the angle of the rotating shaft of the polygon mirror to the incident light and θo is a constant). A reading circuit 32 reads the θj out of the ROM31 according to the counted value of a counter 30 and stores in a latch circuit 33. Driving signals for latch circuits corresponding to respective driving circuits 34 are sent out to respective optical deflectors 35. Their deflection depends upon the frequencies of the supplied driving signals, and the angle of incidence of the light beam to each mirror surface is therefore controlled according to the value stored in the latch circuit. Consequently, the position shift of scanning lines and the position shift of scanning line in the subscanning direction are prevented near the boundary of the partial scanning area.
ABE FUMITAKA
ITAMI SATOSHI
NODA TSUGUO
