Back in the days of film I bought a 500mm mirror lens, not because I needed it but because it was cheap & seemed to be a good idea at the time.
I was using Nikon F801's at the time & only tried the lens on a couple of occasions with varying results.

I got to wondering if it would work on my 50D if I got a Nikon to Canon adapter.
Being a fixed focal length & aperture the only manual adjustment would be the focus.

I am aware of the shortcomings with this type of lens & am prepared to put up with them as I cannot see my way clear to spend a squillion bucks on a conventional 500mm tele lens.

Do I give it a go or return the lens to the junk box in the garage?