Fog Generator
Barn door tracker, also known as a Scotch Mount or a Haig Mount. It can be driven by hand, but by adding a small motor you eliminate the problem of trying to turn the threaded drive rod while swatting mosquitoes. Bending or curving the rod solves the alignment problem caused by a straight rod.
The distance of the drive rod, straight or curved, from the center of the hinge at 1 RPM should be 228.56 divided by the number of threads per inch (tpi), or 1436/tpi/3.1415/2.
The first time I saw one of these it's owner refereed to it as “fog generator” and he would joke that the chance of having a clear sky was inversely proportional to the strength of his battery.
I made this back in the late 1980's. Before digital cameras.
The brass tube is for polar alignment, and needs to be parallel to the hinge.
