I bought my Sigma 17-35 from some company through Amazon. One week after purchasing the lens my AF quit functioning. Sigma would not fix my lense for free because the warranty card I received was not filled out by the dealer! I tried every thing I could to get them to repair it, I even shipped it to them with my Amazon recite, the blank warranty card and a hand written note explaining my situation and problem with the lens. They just shipped it back without touching the lens. After a few months of shooting only with MF my AF decided to work again! But after several more months had gone by the AF began sticking when focusing at the minimal focal range. Soon after that the lens began making a loud "click" sound when zooming in and out right around 25mm and now the lens won't stop down past f/5.6! Due to the poor customer service I experienced and the quality of the lens I received I am sad to say that I will likely never buy a Sigma product again.