Zuiko fish eye is expensive, Sigma hard to find, but the russian Zenitars are readily available... Only problem that the Zenitars are made in Canon EOS, Nikon F and M42 mounts. I happened to have one Zenitar at home, and also a Zuiko 50/1.8 MiJ infected with fungus. Both of these lenses have easily removeable mount. They can be relatively easily swapped (with some drilling of the OM mount to fit the holes on the Zenitar lens). It's really not a difficult to do modification if you use the original M42 mount as template for the holes. This way the lens physically fits OM camera, but: a) cannot focus at infinity (mine could only reach to about 1m) b) metering does not work I don't have a solution for the metering, but it is very easy to get it to focus at infinity. (even without this, the DOF will reach to infinity at f/8 and smaller aperture) To reach real infinity focus, the optics has to be moved closer to the film plane. To do this I had to remove the rubber on the focus ring, loosen 3 setscrews (to disconnect the focus ring from the optics) and move the focus ring so as to enable the optics to focus farther than before (to enable the optics to go closer to the film). I did this and voila - I've got a OM-mount fish eye. I will post pictures of the lens, and from the lens later.