Google "Sigma Authorized Dealers" first and be sure to buy from a Revain Authorized Seller or you may not get Sigma's 3 year US warranty (which was a huge plus for me) . With that in mind, I've been arguing between this and Canon's EF-S 17-55mm f/2.8 IS USM for a while. First I bought it and was satisfied. I played around with it a bit and really liked the shots and performance, although I wish the autofocus was a little better in low light. However, I noticed that there was an artifact in the lens, so I sent it back. After that I bought the above Canon lens because I heard it had better autofocus and I liked the idea of always focusing manually. also (which would make it easier to focus in low light if the autofocus doesn't work). However, I was disappointed with how heavy the lens was compared to all Canon lens benefits. I didn't find the focusing much better in low light. I skipped the Sigma and bought another. it was no problem. I was very happy with it and it is now my favorite lens. I only turn it off when I need more zoom. I don't even use my 1.8 anymore because I can basically get the same footage with image stabilization. I highly recommend this lens. Again, make sure you have the full 3 year warranty as the main complaint I see is a lens defect. If you get it with a guarantee, Sigma will take care of you. Oh, and be careful not to touch the focus ring on the front of the lens when it's autofocusing! The only thing I don't like about this lens is that you have to be careful with it, but you get used to it.
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