M lenses have a far shorter film to rear element distance than R lenses. This means, if you fit them to a Canon EOS (or a Leica R or any other SLR) that you have to put them so far forward that you can only use them for macro or so far inward that you must use mirror lock. In practice: this is impossible. Visoflex lenses are a different story. There are M-visoflex to R adapters that in turn will fit to Leica R-Canon Eos adapters and then they can be used without restriction, fully manual of course.Steven's apdapter should be the same.