I have a 135mm Zeiss Jena lens with a Contax RF mount which I would like to use on my Fuji X-E1 camera. There are adapters for Contax, combo adapters and adapters for Nikon S. The Contax adapters are 200$ while the Nikon adapters are only 20$. They are mechanically compatible but apparently the flange depth of the Nikon is different from that of the Contax.
Does this matter for the 135mm since this is a rather long lens and the back focus should be less critical than with a 50mm.