I picked up one of these recently. It looks like a fun toy, with the
emphasis on toy. It's better than those fisheye adapters that screw
onto the front of a lens, but not by much. There's a lot of lateral
color. You need 35 mm film or a full frame digital sensor to get the
full circle. It looks like you do get the whole 180 degrees in a 19
or 20 mm circle. The lens is fixed focus and has a pre-set diaphragm.
None of that automatic stuff. If you never had to work one of these,
there are two aperture rings: one ring with click stops where you set
the f/stop and one ring that you turn to open up the lens for framing the
shot and then turn back to close the diaphragm to the shooting aperture.
It's a throw-back to the'50s, if not the '40s. The depth of field is
so huge that you are in focus from about 2 ft to infinity. Wide open the
lens is f/5.6 and fully stopped down it is f/45 (!).

Bud