I believe u can do something similar with any *old* camera by connecting it by a T-mount....errr, i think this would be cheaper (for those interested).
I want one of these. (Nikkor 6mm f/2.8) I suppose it is on the complete other end of the spectrum, but who wouldn't want a lens that can see behind itself?
How about a 1540mm lens For those with time and money to burn.