I have read that weeks ago. That's totally different with my experience. Actually you will see many people here have same feeling Sigma 50mm F/1.4 is much better than Canon 50mm F/1.4.
Based on resolution tests the Canon 50 1.4 and Sigma 50 1.4 are both similar in the center but the Canon is much sharper in the corners.
They must have had a bad copy. All other reviews report the Sigma being much sharper wide open, as it was designed to be.
Hmm... don't know about that. LensRentals also noted that the Sigma had softer edges/corners.
DPReview found the Sigma was sharper wide open except in the extreme corners. And you can see the results at TDP. I don't discount the two reviews that show otherwise, but against the body of user reports I think they show production issues / variability.
My suggestion for people cannot make decision between the two lenses is that first get both of them at the same time. And then keep the one you like and return another one.
Good advice. This might also be a lens that warrants cherry picking at a local store.
Regarding AF: I did some tripod mounted tests with the Sigma 50 1.4, Canon 50 1.4 and 1.8, and Canon 85 1.8. I repeatedly manually unfocused, then auto focused each. All of the above showed some variability shot to shot. The Canon 85 was the most consistent, followed by the Sigma, and trailed by the two Canon 50's. It should be noted that AF performance can vary unit to unit as well.
Why did I do this? At first I felt like I was missing more shots with the Sigma. Then it dawned on me that I was also using it wide open far more often then I ever did the Canons. I never really considered them usable wide open except in an emergency. I won't hesitate to use the Sigma at 1.4.
The Canon 50's are gone, though I kept the Canon 85 (great crop portrait and indoor sports lens).