Summary: I have used the Canon50 f/1.4 lens, and also the 50 f/1.2L lens. The 50 f/1.2L lens is stellar, and yes I did experience some focus shift. When it worked, great lens, superb sharpness and contrast. But the focus shift was a source of frustration. I did not like the Canon 50 f/1.4...slower AF, so so results, unless stopped down to 2.8 or so. What's the point of having f/1.4...if it's not useable at 1.4?
Summary: After seeing this was from Adorama, I purchased directly from their website and bypassed the TX sales tax on Amazon, which was nearly $40. On a Canon 5D, this lens focused fast, photos are sharp, the colors are rich, and the bokeh is very nice.
Summary: I had a "nifty fifty" 50mm f/1.8, and a Canon 50mm f/1.4, and neither stacked up to this lens. The image quality is fantastic, the build quality is fantastic, and the Sigma service is amazing. If I could take off half a star for it missing focus EVERY ONCE IN A WHILE I would, but it's not often enough to drop the review to 4 stars.
Summary: I love this lens. As a professional photographer of 13 years, I used both the Canon and Sigma 50 lenses. The Canon 50mm 1.4 is not sharp, misses focus, and is not constructed well (all 3 of them ended up at Canon for repair). I am not very hard on my gear, and my other Canon lenses are just fine. The Sigma is better focusing, sharper, better color and sturdier. Winner in my book.
Summary: One of the best 50mm f1.4 I have ever used. - Very good Image quality. f1.4 is very much usable compared to others. - Solid build - Fast and accurate focus - Beautiful bokeh - This lens is bit wider than other 50mms I believe (may be 45-46mm when I comapred to Nikkor 50mm f1.8 AF). Not a bad thing for me since I am using it in a crop sensor camera.
Summary: I Am so Very Happy with this Lens! It Really Is the Perfect lens for my New Nikon D7000! So Very Fast and Accurate! If you love Taking photos in Natural light without using flashes, this lens will exceed your expectations! Thank You Sigma for a True Masterpiece work of art Lens!!!