Originally posted by StonkinPix With 1 caveat - you'll probably know that the aperture control ring doesn't directly control the aperture opening - merely limits the opening via the camera's own control lever. Therefore, an adapter for the 645 to GFX requires a mechanical aperture control itself. I've found one in the Fotodiox Pro P645 to GFX. Not cheap, but a perfect fit and easy to use.
Welcome to the forum. You could post some of your results in the
medium format pics thread, which is brand and film/digital agnostic.
I'm not sure what you mean about the aperture ring. When not on the A setting on the aperture ring, setting the aperture on the ring stops the lens down to the specified aperture and any "dumb" adapter which just provides a tube with a Fuji lens mount on one end and a Pentax 645 camera mount on the other will do.