The focusing and collimating lens array provides the laser beam with the sharpness and precision necessary to accurately charge the drum. When the beam leaves the laser source, it must pass through a collimating lens to insure that the beam is parallel (that is, the edges of the beam do not diverge and the beam does not become diffuse over distance). The collimated beam then passes through an electronic shutter which cuts the beam into short blips, or flashes of light. The timing of these blips is controlled by the computer. The blips then hit a rotating mirror which scans across the drum, charging the appropriate pixels. A lens between the mirror and the drum compensates for reflection so that a blip is no more diffuse at the end of a line than at the center. Without this compensating lens, the image would be less defined at the edge of a printed page. This optical system is a delicate one, and can easily be knocked out of alignment.
