See my Sigma DG HSM Art wishlist.
I wont’t be able to post much from the field this trip—just too short a time. Full coverage will have to wait until I return home. Shooting in snow is hard to do for many reasons, but mainly access/slogging.
The Sigma 40mm f/1.4 DG HSM Art is a spectacularly good lens—the best yet from Sigma, impressive by just about any standard. I rank it up there with Zeiss Otus lenses overall and yet it falls grievously short in one key area: pronounced (stunningly unexpected!) focus shift (flare resistance is also a concern).
Add in troublesome front-focusing errors on the Nikon D850, and the Sigma 40mm f/1.4 DG HSM Art is a sort of idiot-savant lens in that front-focus errors tend to cancel out focus shift by f/2.8 or so, so that sorts itself out, which is good or hundreds of shots would have been junk. Problem is, using Fine Focus Adjust to cancel out focus errors for f/1.4 and f/2 screws up stopped down performance because the focus shift no longer cancels-out the AF error <gah!!!!!>run screaming into creek to wake from bad dream</gah!!!!!>.
Correction for secondary color is among the best I have ever seen wide open at f/1.4, though the image below is stopped down, it looks just as good in terms of color at f/1.4.