I didn't know you can do that. How much of the sensor do you lose and how are the edges? I rent the GFX100 for a client occasionally and it's just a question of time before I pick one up. The 100 has a pixel pitch of 3.7 or so, smaller than the Z9, and I'm curious how the crop would look.
It depends on the lens.
You can shoot adapted lenses on the GFX100S without any crop... you'll use the whole sensor. With many lenses you'll get hard vignetting in the corners, but some lenses have a large enough image circle to cover the entire GFX100S sensor.
You can also use "35mm mode" on the GFX100S, which will crop the sensor down to 36x24, effectively making the camera act like a "Z7". But I always shoot the full sensor, because most lenses cover (considerably) more than 36x24, and oftentimes I'm shooting at XPan or 1:1 ratio anyway, which pretty much
any lens can cover fully. "Capture it all and crop it later" is my method.
In any case, there are autofocus-capable adapters available for both F and EF mount. The "Fringer" brand is probably the best for both right now. They even support lens correction profiles and insert proper EXIF into the photos on your GFX100S, and the EF version has a nice aperture ring.
This is a huuuuge rabbit hole to go down if you want to research more. There's a bunch of people at the Fred Miranda forum shooting adapted lenses on GFX that you can chat with. For my part, I use:
Nikon F:
- Nikon 58/1.4 - Full coverage, corners are a bit mushier than on FF until you stop down to f/2.8
- Nikon 105/1.4 - Full coverage, no issues at any aperture
Canon EF:
- Tamron 45/1.8 - Full coverage, corners somewhat soft wide open but good by f/2.8
- Canon 70-200/4 (non IS) - MOSTLY full coverage, but the closer you get to your subject and the closer you get to 135mm, the more the vignette creeps in. Worst case I've gotten 90 mpixel on a 3:2 crop. Sharpness is best at f/8, but usable wide-open
- Sigma 105/2.8 OS Macro - Full coverage, but a bit soft at infinity... especially wide open. Get closer or stop down.
Minolta Rokkor 58/1.4 - Good luck focusing accurately! Looks great if you can nail it at f/2.8 and smaller, or like a 70's portrait effect wider than f/2.8.
If you want a good wide-open performer, you'll have to do your research and take what you can get as far as adapted lenses go. There's definitely some diamonds in the rough. I got three outstanding AF primes for the cost of a 110/2, but it's certainly easier to hand B&H your credit card and have them just figure it out.
