I am a big Sigma supporter as I believe that their glass is great... until there is an issue (product developed fault, bad copy , etc.). My problem is that I cannot get Sigma Distributor to even understand what the issue is. I guess, same as with SONY support - they simply do not know good from bad.
example:
I purchased brand new Sigma 50 1.4 Art for my daughter at very good price and decided to run lens calibration test to verify the lens AF and sharpness is at least good.
I quickly found that the lens required extreme AFMA out of the box and was outright soft even when calibrated.
I took the lens back to Sigma service centre and explained the problem. People at the SIGMA centre were very friendly and nice (as usual) and offered to adjust the lens while I was waiting.
I was advised, that the lens firmware was adjusted to focus correctly at x40 the Focal lenght ( 2.0m) distance. Great, and what about lens being really soft? It turns out, that they do not know how to verify the lens sharpness is within manufacturer's specs.. Seeing that the softness is likely was not adjusted, I requested the lens exchange and my request was granted.
I took the lens home, calibrated AF on Sigma USB dock at 04m, 0.7m, 1.5m and at infinity (10M)
Sharpness of this copy was good, but not excellent (Reikan Focal 1700 AF points vs 1900 AF points of my older Sigma 50 1.4 Art).
While the lens focused very consistently for me and right on the money at the calibration points ( 0.4, 0.7, 1.5, 9-10m), I found that at 2.5 - 7 meters distance AF was off by a substantial margin. that cannot be adjusted on the dock. SO.. I took the lens back to Sigma service centre this morning and explained what was the issue and asked them to see if they can do something about it. I was given straight answer, that they never ever delt with anyone that demaned such a service and that there is nothing wrong with lens. it is good at all 4 focus distances and why I even brought this issue up. Sure, I was offered full refund that was accepted. Great

)
So my point is : you can make Sigma Art lenses work.. with a little bit of luck. Great if you are lucky. I am not..
Redline said:
Not that I'll be buying the IV any time soon glad to have read this since I do love my Sigma lenses.
I mean aside from innovation I'm sure Canon knew for so long of the popularity of the 3rd party lenses not to mention both Tamron & Sigma have been upping their game hard. It only makes sense to offer features not available with other manufacturers and stay competitive.