So I've been playing with the 35/2.8 C-Biogon on the Fuji adaptor. Fuji claims that it's not a compatible lens and the gauge that comes with the lens indicates that the back elements are too large in diameter to fit. But it does in fact fit without any mechanical interference. Or, at least, my particular C-Biogon fits my particular Fuji adaptor without interference.
Your mileage may vary, please proceed with caution!
The results: absolutely stellar! Sharp to the edges even at 100% crop. I also have the XF 35/1.4; the baby Biogon is at least as good, and it's easy to manually focus, too. I am VERY happy with this setup. So much so that it means the XF is now a specialist lens for shallow DoF, lower light, or closer focus. I may sell the XF.
I still need to do a little work to see if the baby Biogon has any color shift in the corners that requires compensation. If there is, it's subtle. A truly winning combinationl
As an aside, looking closely at this adaptor it has some *very* striking similarities to the Novoflex adaptors, so much so that I'm starting to wonder if Novoflex manufactured all or part of the assembly. If they did (and if you look at the prices of other
Novoflex adapters, $200 for the Fuji adaptor starts to look like a bargain.