This shootout on the 45-megapixel Nikon D850 pits the Zeiss Otus 28mm f/1.4 against the Sigma 28mm f/1.4 DG HSM Art.
This comparison turns out to be far more informative than lab tests. Real-world depth of field, field curvature and focus shift all come to bear and in that regard the two lenses differ markedly. Both are very fine lenses, but differ in behavior.
In diglloyd Zeiss DSLR Lenses:
Shootout: Zeiss Otus 28/1.4 vs Sigma 28/1.4A: Alabama Hills Creek to White Mountains (Nikon D850)
Includes images from f/1.4 through f/13 at up to full camera resolution, along with extensive commentary and conclusion.
Alabama Hills creekbed after heavy rains all night
f1.4 @ 1/2000 sec, ISO 64; 2019-03-06 11:11:53[low-res image for bot]
[location “Alabama Hills”, altitude 4700 ft / 1433 m, 56°F / 13°C, polarizer=Zeiss, Enhance Details]
NIKON D850 + Zeiss Otus 28mm f/1.4 APO-Distagon