You'll find very few Tektronix manuals online for a couple of reasons:
1) They're huge. My manual for the 7834 is about 2" thick. (I have a 7834. They never made a 7384.)
2) The schematics are on fold-out pages, much larger than 8x10, and multi-colored. Monochrome copies are very hard to follow.
The supply voltage (top pin) on my 7834 measures +15.145 volts, so it is regulated in the 'scope.
The middle pin is the trigger to the camera, and appears to go to ground briefly (did not investigate fully).
The bottom pin is ground (0 volts).
The "single sweep" mode was used for recording transient events. These might be predictable, like the inrush current of a motor
when you start it up, or unpredictable like a failure or fault condition. The camera would be triggered by the 'scope when the
sweep was initiated, making the system totally automatic. One sweep could take up to 100 seconds.
The NO and NC outputs would be used for starting external devices, like a chart recorder or similar. The oscilloscope could be used
to initiate recording of data over a very long period of time, like hours or days or longer. No flash was used with these cameras.
I expect the Remote input requires a contact closure, like a pushbutton, but I may be wrong. I never used that feature.
I wouldn't be inclined to waste much time on 'scope camera optics. The lenses were not of high quality, and were optimized (if at all)
for roughly 1:1 reproduction ratios.