Like Nick said. He actually has the one I'd previously bought from Cameraquest. Very simple to use - just set the aperture reading on your Canon body to its widest (either f/1 or f/0 depending), and don't touch it again while using the C/Y mount lens, ie, the aperture must be set on the lens only, otherwise there will be exposure errors.
-------------------- Tim BSRIPN
You see something happening and you bang away at it. Either you get what you saw or you get something else--and whichever is better you print. - Garry Winogrand