First of all, let’s take a look at the results for the Sigma lens by itself:Sigma 17-35mm F2.8-4 EX DG Aspherical HSM Canon mounted on a Canon EOS 1Ds Mark IIIWith a DxO Mark Score of 20, this wide-angle zoom is indeed a good-quality lens.Strong pointsWeak pointsGood sharpnessSignificant vignetting at maximum apertureGood correction of chromatic aberrationRather weak transmissionVery reasonable price An acceptable weight ComparisonSigma 17-35mm F2.8-4 EX DG Aspherical HSM Canon vs Canon EF 16-35mm f/2.8L II USM mounted on a Canon EOS 1Ds Mark IIIBoth lenses achieve the same DxOMark overall score of 20. When looking at the