Due to the lack of dedicated telephoto lenses for Leica’s S medium format system, this gentleman made his own R->S adapter to use R-mount telephoto lenses on his Leica S2. Apparently, the image circle of these lenses is large enough to cover the whole S2 sensor. Allegedly, he already contacted Leica about the adapter, as he definitely sees a market for adapting R-mount lenses to the S2. Very awesome!

He was taking pictures of penguins with this combo, btw.

Leica S2 + APO Telyt-R 400mm f/2.8 at the Frankfurt zoo