I once owned a Kodak microfilm camera / viewer, probably 1940's vintage. It had a microfilm camera on top, along with a light source and microfilm feeding mechanism for projecting roll microfilm onto a white screen at the bottom. Basically a box about 3 feet high , 2 feet wide & deep, open on one vertical side. Papers could be placed at the bottom for copying with the built in camera, or roll microfilm viewed on a white screen in place of copy materials.
Although it only copied one frame at a time, there were 2 buttons to trigger the camera. The buttons were large, almost the size of the palm of your hand. Both buttons had to be depressed simultaneously to trigger the camera. This seemed to be a strategy to guarantee the cameraman's hands would be out of the field of view when the copy was made. The buttons were large enough and easy enough to press for a person not to experience hand strain even after hundreds of pages, The fingers & hands still might develop repetitive strain, just from placing and aligning the source material on the base of the device. There was no automatic sheet feeder. I forget how the roll of developed microfilm was advanced during the viewing process.