Wow, that reminds of when I used to have to align our imagesetters here at work. Same principal for projection as the one you are using. We needed lenses to focus the laser beam to a 1/1240 inch dot and the laser was always on with a vibrating (oscillating) mirror in the laser beam path instead of pulsing the laser . The oscillating mirror was close enough to the laser that it didn't require a large movement to direct the beam either on the mirrors or away from them as the path to the polygon was in the order of maybe 3 feet. A rotating front face mirrored (8 sided) polygon spun to provide horizontal imaging and the film was moved under the beam to produce a negative for a newpaper page.
I don't think there were microprocessors back then so it almost all was done with discrete components and ICs.