I just got a new Fujinon-C 600mm and noticed that the Copal has markings only down to f/64. In fact, the shutter can be closed down way way more. Is your Fujinon-C 600mm in the same situation? The Copal on my G-Claron 355mm has markings down to f/90 and on my Nikkor 450mm to f/128.
Can the performance degrade so much beyond f/64 that Fuji does not recommend to use the lens closer than f/64 and therefore did not put markings beyond that? I find it hard to believe. Sure, I can guess pretty much where to move the lever to get f/90, but it is a bit of a drag.