On 2011-12-21 12:56:56 -0500, William Hamblen said:

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

That kind of aperture setting was called "pre-set" as opposed to "auto"
(the aperture stayed wide open during framing and closed down to what
you set it at when you took the picture, doing so "automatically").
These lenses were very common in the 1960s and even the 1970s as low
cost alternatives to the "auto" lenses. I think they started to
disappear when lenses became automatic in the sense we think of them
today.
--
Michael