So, my experiment with Canon lenses didn’t go so well. Preliminary tests were acceptable but didn’t perform well at all during practical use. While the 135mm ƒ/2L was ok, the actual output was less than stellar due to significant vignetting. While the 135mm was borderline, the 28mm ƒ/1.8 was atrocious. Both seemed to be affected by the baffles in place over the rear element. That baffle seems to be designed to prevent reflections from stray light within the mirrorbox but were obviously cut to fit a 3:2 sensor. That means they interfere with a taller sensor, like the 4:3 ratio of a 645 medium format sensor.
I decided to send the lenses back and go with Sigma. Their reputation for compromising size and weight for image quality, plus their use of a slightly larger imaging circle to ensure a larger sweet spot hitting the sensor gave me more confidence in their ability to fill a 645 sensor completely. To be sure, I tested out all of the desired focal lengths at Glazer’s Camera to ensure any vignetting is acceptable to me. From there, I chose the 35/1.4, 85/1.4 and 135/1.8, with Fujifilm GF 23/4, 45/2.8 and 63/2.8 filling in the holes affordably. To make this happen as quickly as possible, I made the difficult decision to trade in a few XF primes I hardly use, keeping a range of zooms only for the X-T3. But I digress…
The Sigma 85mm seems to cover all of the imaging sensor with no hard vignetting. Fitment of a Wine Country Cameras 100mm filter holder does cause some very light vignetting at the extremes but is easily correctable. Image quality at the extreme corners and edges is a bit compromised at wide open but shapes up when stopped down to ƒ/4.
Latest firmware installed on lens.
Autofocus works quickly throughout range.
Continuous AF is nervous and fails to lock; completely useless.
Eye AF does work but is less confident than a GF lens, often dropping back into face detect.
Samples:
Only you can decide if an adapted lens will work for you but in the case of the Sigma 85mm ƒ/1.4 DG Art for Canon EF, this is about as good as it gets for image quality and sensor coverage. Autofocus isn’t perfect, far from it, but for landscapes and studio portraits, it should work well, especially in situations where you have the time to manually focus or punch in for critical focus.
JetCity Ninja 
Hi there…thanks for these posts. I am considering this Sigma 85 as a temporary replacement for the GF 80, as it’s way hard to find at the moment in Vietnam, and I don’t really mind paying 1/3 of the price either. Taking into account the lens shortage + the price, could you make a recommendation for this Sigma 85? Any input would help. Also, have you tried the Sigma 105 Art?
I deeply apologize for my late response and hope it still proves somewhat useful.
I’ve owned the Sigma 1.4/85 and it’s an excellent lens, however, it lacks the character prevalent in the GF 80mm. The main thing is to not skimp on the adapter. I highly recommend either the TechArt, Fringer, Metabones, Steelsring, or Fotodiox Pro Fusion. I have used all of these at some point and they’re all great but they’re listed in order based on my opinion of their reliability and stability, from my first choice to last.
However, you will not be able to rely on autofocus unless you’re using the GFX 100 or 100S. It’s terribly slow and unreliable for continuous AF and too slow to be useful in AF-S except for static subjects. I use back button focus plus AF+MF in AF-C mode simply to get me close then fine tune focus manually.
So yes, if I were in your position, which I have been previously, I’d happily grab a Sigma 1.4/85 as long as my expectations are well tempered. I have not used the 105, aside from mounting it and playing with it for a few minutes.
Again, I apologize for the late response and appreciate your finding my blog.
-o
For some reason my 85mm WILL NOT communicate the aperture or AF. Displays F0 and I have to manual focus. Have you ever ran into this issue or have any idea what this is? I’ve updated the adapter to V2.0.
Sorry for the late reply. Try twisting the lens and adapter against the locks. Sometimes the lens and/or adapter has enough play to be twisted slightly past the electrical contacts. Just try turning the lens and adapter both directions until you hear it click, ensuring the locking pin has snapped into place.
This is what caused mine to do exactly what you described.
Thanks for the response.
I actually returned this adapter for the Kipon adapter. I’m thinking with Sigma’s newest firmware update on the 85mm there is some sort of firmware miscommunication, or I just received a faulty adapter.