Hi, I had looked at that link yet it didn't seem to resemble any of the mounts there but I think that would be due to be to the clarity of pictures on there. The lens is a Vivitar 28mm f/2.8. Thanks for the advice regarding measurements, I wouldn't have thought to do that. The bayonet actually seems the same size as my Nikon lenses except for the small gap in one of the flanges (top right in original photo) and the bit making me most apprehensive is the big prong sticking out of the mount.