Canon PC940 Service Manual - Page 52

CHAPTER 3 EXPOSURE SYSTEM B. Varying the Reproduction Ratio The reproduction ratio in the drum axial direction (main scanning direction) is varied by the lens drive system, and that in the drum peripheral direction (sub scanning direction) is changed by the scanner drive system. In the lens drive system, the positions of the fixed focal point lens and the No. 4/5 mirror are changed to vary the reproduction ratio. In the scanner system, the relative speed of the No. 1 mirror mount is made higher (for reduction) or lower (for enlargement) than the drum peripheral speed. Direct Optical length F' F L1 Reduction Optical length F' F L2 F' Enlargement F Optical length L3 Optical length: L1 < L2, L1 < L3 Figure 3-102 3-2 COPYRIGHT © 1999 CANON INC. CANON PC800s/900s REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)