I bought and returned 2 of these to Amazon. I was using with Canon 80D and found both to have major back focussing issues. I managed to do some corrections but never got them fully working. I didn’t feel it was sensible to keep a £1000+ product I had to fix myself! I would be interested to see if other people experience the same problems (this topic doesn’t come up in any reviews I’ve seen).
This Sigma 24-70mm Art lens is simply superb. Image quality is very sharp with great contrast, throughout the entire zoom range. This holds true even when shooting at the widest aperture, which gives beautifully soft and smooth rendition for defocused areas within a scene. Colour fringing, distortions, ghosting and flare are all minimal. Build quality and handling are great and, although it's not a 'weather-sealed' lens, a rubber gasket on the mounting plate helps to avoid the ingress of dust or water between the camera body and the lens. Autofocus is fast yet very quiet, and the optical stailizer has an effectiveness of about 3 to 4 stops.
I write camera and lens reviews for a number of photography magazines and use both Canon and Nikon DSLRs. Faced with the choice of which standard zoom lens to buy, and after testing all the options, I went for this Sigma lens in preference to both of the equivalent top-grade Canon and Nikon 24-70mm f/2.8 lenses. I don't regret it for a moment.
I purchased this lens from Wex Photographic a couple of weeks ago but had to return it as it's horribly soft. I tried using the Sigma USB dock to do some micro adjustments, however found that it didn't help. Using the lens at 24mm I found I had to stop down to about f8 to achieve a level of sharpness that was "satisfactory". Throughout the rest of the focal range, it was ok from about f5.6 and smaller. I did not expect a brand new Sigma Art release to be as much of a disappointment as this was. Seeing as f2.8 is unusable, you may as well go for the Sigma 24-105 f4 Art for much better sharpeness and a fraction of the price.