Where the Sigma 85/1.4 is a home run, the 35/1.4 is a bit of a mixed bag. For most people, it should be fine. For some, like me, it's borderline acceptable. For those few, it will be unacceptable. In 35mm crop mode, it works just fine, but for any other mode, it will require a bit of cropping and correction. At wide open, there is a bit more smearing in the extreme corners that sharpen up by ƒ/4 to 5.6.
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.
Despite white wall tests of the Canon EF 28mm and 135mm lenses showing acceptable levels of vignetting, my first real world use of them ended in failure.
Eye-AF works pretty well with this combination. Focus is slow, but it's able to find and lock onto an eye. Because of my experience with the X-T3, sometimes my expectations can be a bit skewed; face and eye detect on the 2018 X-T3 is quite good, especially on distant (small) faces as Fujifilm has improved by leaps and bounds in this area. How quickly I forget the GFX 50S is over a year and a half older, with an imaging processor based on the X-Processor 3 design in the X-T2 and not the current X-Processor 4. Combined with other hardware limitations, plus the fact that the latest firmware update was over a year ago, eye AF on the GFX 50S (or 50R, for that matter) cannot be expected to perform anywhere near that of my X-T3.
There are some drawbacks though. Uncannily enough, they’re the same as with the Canon EF 28mm ƒ/1.8 USM: slight vignette with a hard vignette at infinity focus. At ƒ/8, it isn’t very prevalent as you’ll see in the samples, easily corrected with a 5:4 crop that retains 48MP. However, as the aperture gets smaller, the vignette hardens, as you can see at ƒ/32, but still works at a 5:4 crop ratio. The lens works fine with a 3:2 crop at full sensor width and in 35mm crop mode, so you can choose what works best for you. Weirdly, the lens changes focus as you move in and out of playback mode on the GFX...
Widening out to an approximate 22mm in 35mm format terms, the Canon EF 28mm ƒ/1.8 USM does show some hard vignetting that is never fully resolved. It’s very, very slight and occurs at ƒ/4 and smaller at infinity focus. Vignetting is prevalent fully open, mostly disappearing by ƒ/4 at close focus distances. If the vignetting is a problem for you, the EF 28mm ƒ/2.8 IS might be a better bet but isn’t on Canon’s list of preferred lenses for the 5DSR, so it may or may not resolve well on a 50MP sensor.
As soon as I realized how the upright on the Ellie interfered with my battery door, I was able to devise a cheap solution for manufacture: a small bracket that would accept the rails and to attach the upright with truncated rails, aka screws, forward of the current position. I proposed the question to @3leggedthing's Twitter account, only to get, "we can't design a specific bracket for every camera and configuration I'm afraid."
Here's one of the first things I do when I buy a new camera: Secure the screws that secure the tripod screw port on the bottom of your camera.
After spending a few weeks with the Sigma 50mm ƒ/1.4 Art, I've come to realize maybe Sigma lenses aren't the solution for me. At least the 50mm has a very short focus throw, making manual focus a tedious process, even with focus aids like focus peaking and focus zoom. Autofocus is just too unreliable and slow to depend on for all occasions, making manual focus capability a priority.