Everything has been said Sigma. Especially trouble. So here is my version. Enclosures: 5D mk II, 50D Use: professional Purpose of purchase: a long zoom, maximum dive (for a long zoom, so to 400mm, it's less than a quilted premium) for outdoor pictures (landscapes, nature, meetings, sports, journalism etc. .), fast AF and stabilization. Using hand raised to 90%. In the running: the Sigma and the Canon 100-400. Predictable problems (reputation) and admitted: bad series (yes, also for the Canon), back focus, AF slipping. As 100-400 is as controversial as the Sigma, but for double or triple the price, I took the Sigma. Purchase of the beast. Bad run (back focus, etc.). Do not panic. The black card allows Sigma, hang, calibration and adjustment of your goal, to life once a year! So sending Sigma (before a mail to prevent) and 3 days later the objo is back, ready to use. 3 days! Nothing to say. So what happens? AF perfect: Catch a seagull (and keep it in focus) to 400mm in high winds, freehand ... it does. Approximately 10% waste from destroyed homes. Stab: If you wait 2 seconds, it will hold, and it moves. But must wait 2 seconds. Very effective, but rather curious, he "hold" really. It feels hesitating, and suddenly, pof, it is inside. The stab reminds me of that of the Canon 100mm Macro L IS (excellent, too), and is much more effective than other Canon. Piqué: aaah, sharpness. This is the big argument. The pixel peepers will say that the Sigma is not good. Again, the large premium Canon (or Sigma) are much more sharp, but it is not the same price and the same use. Nobody has a 100% view either. Sigma, without having to go to f8 is very good 120 to 250 and ... very good 250 to 400. By being objective, I would say it is sweet. Not soft, but soft. Pictures are not clinically clear, but almost enjoyable, warmer, rounder than those objectives "tack sharp". By comparison, this is exactly the difference of a computer screen (or TV) Classic (high quality) compared to one with a flat screen. Much more enjoyable. Basically, it makes great pictures, pro quality, but it excels in some areas and in other plant (photos twilight, evening, etc.) He needs light. Pictures sunlight are superb. The bokeh is to die for (much more beautiful than a 70-200 f2.8) In short: a very endearing and very efficient objo capable of beautiful shots. It's not a studio objective or macro and it does not replace a premium, but like any high quality field, it equal, see above in my opinion the Canon 70-200. Matter of taste.
