I just stumbled across an eBay auction for an "Ewar" 12mm/f8 ultra wide angle lens (120465778111):
It looks like it's in T2 mount, which would make it adaptable to most cameras.
Does anyone know this lens? Is it a rectilinear lens or a fisheye? There were a number of 12mm third-party fisheyes, but they usually say "fisheye" somewhere in the lens name. This one has "Ewar ultra wide angle lens". When were they made?