Stereo F2 macro
Nikon made a stereo lens for their rangefinder cameras, but very few were made and it's now a highly prized (and highly priced) collectors item. Since Nikon did not make a stereo lens for their SLRs, I made one myself for under $30.
My stereo macro lens on an F2AS The mirror has to be locked up, as a deep shield is needed to completely separate the stereo images
The lenses came from a Nimslo camera, and mounted back to front. The focal point is fixed at about 120mm in front of the lens. Incidentally, my Nimslo is now a stereo camera, without the middle two lenses The stereo lens viewed from the back of the F2.