My choice was either the Canon 17-55mm f / 2.8 or SIGMA 17-50mm f / 2.8mm. I have found no technical arguments or user reviews to guide my purchase for CANON twice as expensive and not equipped with the new sun visor. Upon reflection, so I opted for the SIGMA and do not regret my purchase. The objective is beautiful and the first convincing tests. Its sharpness is beautiful, fair and true colors above the 18-135 CANON I own. The distortion in wide angle is quite acceptable. I have not really tested in low light, but its linear opening 2.8 and its stabilization can not disappoint. I read that the weight bothered some users, yes it's true it's 565 grams, it's just the weight of quality. I suggest strongly that SIGMA 17-50mm f / 2.8. Also before concluding I am awarded 5 stars to Amazon for the responsiveness of the order I made him for this purchase.