Amazing highly technical stuff, amazed at the rig he used that could perfectly track stars across the sky (there are no star trails anywhere). I'll let him explain better:
It was clear that such a survey would be quite difficult visually hopping from one area of the sky to the next—not to mention possible lapses in coverage—so this called for a more systematic approach. I divided the sky into 624 uniformly spaced areas and entered their coordinates into the computer which gave me assurance that I was on target and would finish without any gaps. Each frame received a total of 60 exposures: 4 short, 4 medium, and 4 long shots for each camera which would help to reduce the amount of noise, overhead satellite trails and other unwanted artifacts.