Panasonic FP-D250 User Manual page 69

(5) f-θ lens
• A lens that causes the parallel light reflected from the polygon scanner to fall
on the drum. It is designed so that transmitted light curves toward the optical
axis around the lens with a large scanning angle so that the incident light that
swings at a constant angular velocity becomes a constant velocity scanning
for the drum. The recording width is the length of the short side of Ledger/A3
size paper and the light spot is approx. 42 micron.
(6) Synchronization signal detector (synchronization sensor)
• To accurately detect the position of the laser beam in the main scan direction
during drum scanning, and to minimize positioning deviation of the image on
adjacent scanning lines, it is positioned just before drum face scanning during
the scan of each face of the polygon scanner to detect laser beam transit
timing. Polygon scanner mirror face division error and uneven rotation
compensation is provided by image write start in accordance with this timing
signal. A pin photodiode with a fast response is used for the detector.
Sync Sensor
2-32
f-θ lens
Paper feed direction