just as sharp right in the center as the $4000 Zeiss 55mm ƒ/1.4 Otus, lens, while the Otus shows better sharpness in the corners
stop down to ƒ/2.8, the Zeiss 55mm and Sigma 50mm show very similar, very sharp and very flat blur characteristics
At ƒ/1.4 and on a full-frame camera, it pretty well blows all of the other 50mm lenses out of the water. The Canon 50/1.2L is pretty sharp in the center, but the corners are extremely soft. The Nikon 58/1.4 is less sharp in the center, and quite soft in other parts of the frame. The Sony 55/1.8 obviously doesn't get to ƒ/1.4 at all. The other lenses all improve at ƒ/2, but so does the Sigma 50mm, easily bettering all comers, at every point across the frame
1EV vignetting, almost immeasurable geometric distortion
less CA than the Canon 50mm f/1.2 but a little more than the Nikon or Sony
doesn't feel like the fastest AF in the world when racking all the way from minimum to infinity focus, which takes around one second