This is a summary of information comparing the Nikon 50mm f/1.4G AF-S Nikkor and Sigma 50mm f/1.4 EX DG HSM (Nikon mount) lenses.
Nikon 50mm f/1.4G vs Sigma 50 f/1.4 (Nikon mount): Performance vs Aperture Range
Thom Hogan summarizes the respective performance characteristics of the Nikon 50mm f1.4G AF-S and Sigma 50mm f1.4 EX DG HSM lenses across the aperture range:
The Sigma is worse than the Nikkor at f/1.4. If you’re buying the lens solely for maximum aperture, I’d get the Nikkor. But the Sigma improves considerably at f/2, the Nikkor less so. So in the f/2 to f/4 range the Sigma may be the better choice (true on DX, less so on FX due to corners). From f/5.6 onward, the difference is really only that the Sigma’s corners are a bit weaker than the Nikkor’s.
Nikon 50mm f/1.4G vs Sigma 50mm f/1.4: Coma Distortion
To a question on which lens handles coma distortion better, the Nikon 50mm f/1.4G AF-S Nikkor or the compatible Sigma 50mm f/1.4 EX DG HSM lens, Thom Hogan replied:
The Sigma is better at coma handling than the Nikon. I don’t have a good testing procedure I trust for coming up with specific evaluation there, though (e.g. how much better), which is why I don’t report it.
Nikon 50mm f/1.4G vs Sigma 50mm f/1.4 (Nikon mount): AF Speed
Thom has the following comment in response to a remark that since the Sigma 50mm f/1.4 EX DG HSM has a faster AF (autofocus) compared to the Nikon 50mm f/1.4G AF-S Nikkor, then the AF motor on the Sigma lens must be of professional grade, while the one on the Nikon is a lower-grade, and lower-priced version:
It’s not the grade of the motor, it’s the way the focus elements are designed in the two lenses. The Nikon sacrifices fast AF performance for a very long focus throw (which also shows up as an ability to manually focus it more precisely). The Sigma has a very short throw — it’s obviously not moving the focusing element(s) much.
Nikon 50mm f/1.4G — Main page
Sigma 50mm f/1.4 EX DG HSM — Main page