Update on 27 July 2012: new sample photos (full res available for download)
Today I am comparing two “premium” third-party standard zoom lenses: the Tamron 17-50mm F2.8 VC ($650, B&H), and Sigma 17-50mm F2.8 OS ($670, B&H). Both offer a useful 17-50mm with fast F2.8 max aperture (at all focal lengths). Both feature optical stabilization. Both are available for multiple camera mounts (including Canon, Nikon and Sony).
In addition to their similar specifications, these two have very similar size and weight, and compete in the same price range. Direct competitors, therefore. But which one is best?
I got my hands on both of them (Nikon mount), and put them to the test.