Camera Labs

I'm currently looking at one of the above lenses. I have a Nikon D5100 with both kit lenses but will be soon upgrading to a D7000 body. I plan on selling the D5100 with both kit lenses so will not have a short zoom lens. I currently have the Nikon 50mm f/1.8 and the Nikon 70-200mm f/2.8 and would like a good quality lens to fill the gap. I shoot mainly portraits, sports and nature and due to the low light requirements would prefer something that has the 2.8 option. I have read many reviews on both lenses but would like some feedback from forum viewers that have either of these lenses and what they would suggest. The Sigma is signficantly cheaper but I've heard they can have QA issues, others have said they have had no issues and that it is a great piece of glass. I am more worried about the AF speed and build quality, I have heard the Nikon is superb in every aspect.

Your comments are much appreciated.

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Nikon D5100, Nikon 70-200mm f/2.8, Nikon DX AF-S 18-55mm f/3.5-5.6G, Nikon DX AF-S 55-300mm ED f/4.5-5.6G, Nikon DX 50mm AF-S f/1.8G, Manfrotto 290 Tripod and Infrared Remote

Tamron also make one. The 17-50mm f/2.8 SP XR Di II LD, non VC version, is pretty highly rated. Arguably the best bang for your buck in that lens category.

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Canon Powershot S95, Canon 7D, 15-85, Canon 85 1.8 USM, Sigma 30 1.4, 50mm 1.8, Canon 100 2.8L IS Macro, Canon 70-300L IS USM+Kenko 1.4 Pro 300DGX, Canon 430EX II and RS 4 Classic