Sigma AF 12-24mm f/4.5-5.6 EX DG HSM - Review / Lab Test Report - Analysis
Lens Reviews - Nikon / Nikkor (APS-C)
Article Index
Introduction
Analysis

Distortion

The Sigma shows a quite unique distortion characteristic for an ultra-wide angle lens - it is extremely well corrected here with only minimal distortion even at 12mm. The lens is basically free of distortion at 24mm. The remaining distortion is slightly wavy in style though.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
12mm 17mm 24mm

The chart above has a real-world size of about 120x80cm.

Vignetting

The Sigma is a full format lens thus enjoying a sweet spot advantage on APS-C DSLRs. At 12mm vignetting is still quite pronounced although not excessive at f/4.5. At all other settings the problem is very well controlled for such a lens.

MTF (resolution)

The Sigma AF 12-24mm EX produced very good resolution figures throughout the tested aperture and focal length range. There're competing lenses with a better center performance out there but the resolution characteristic is unusually even across the APS-C image frame - even at the extreme borders at 12mm. A nice side effect of the full format nature of the lens.

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

The Sigma has not many weaknesses but it has definitely one - lateral CAs (color shadows at harsh contrast transitions). At 12mm and 17mm CAs are quite extreme and not really acceptable unless corrected via imaging tools (like most RAW converters). The CA situation is quite good at the long end of the zoom range.

Verdict

The Sigma AF 12-24mm f/4.5-5.6 EX DG HSM is the most extreme full format ultra-wide zoom lens around and it is still a "mainstream" ultra-wide lens when used on APS-C DSLRs. If you're looking for a future-proof "duo-format" lens in this class - well, here it is. However, there're a couple of further good arguments in favor of the lens. In the APS-C scope the resolution is very high and even throughout the tested aperture and focal length range and as such more harmonious compared to dedicated APS-C zooms which tend to suffer from edge problems. Distortions are extremely well controlled for a lens in this class and vignetting is generally not a problem except maybe at 12mm @ f/4.5. The only significant issue are lateral CAs at and below 17mm - you better shoot RAW files and correct the issue in your RAW converter, otherwise CAs are too extreme. The build quality of the Sigma is excellent and the fast and near-silent HSM (ultrasonic) AF drive is a welcome feature. The price tag of the lens is fairly moderate in relation to what you get for your bucks. Highly recommended ... if you can get a good sample (the tested sample in Canon mount wasn't quite as good).

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