Sigma AF 12-24mm f/4.5-5.6 EX DG - Review / Lab Test Report - Analysis
Lens Reviews - Sony Alpha/NEX (APS-C)
Thursday, 28 February 2008 11:58
Article Index
Introduction
Analysis

Distortion

The Sigma shows a very seldom distortion characteristic for an ultra-wide angle lens - it is extremely well corrected here with very low barrel distortion even at 12mm. The lens is basically free of distortion at 24mm.

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 @ f/4.5 vignetting is still quite pronounced although not excessive. 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 border resolution remains unusually high within the APS-C scope - even in the extreme corners at 12mm. A nice side effect of the full format nature of the lens.

That all said I need to mention that the tested sample was not the best ever lens that has reached these shores - it showed a quite significant centering defect towards the 24mm setting. Centering problems tend to show up as local focus defects (within the image field) so this had no major impact regarding the lab analysis. The performance figures are also pretty much in line with the results of the Nikon variant 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)

Technically 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 although via imaging tools (like ACR). The CA situation improves towards the long end of the zoom range.

Sample Images

As mentioned the lens suffered from a rather pronounced centering problem so no sample images this time. <ü>

Verdict

The Sigma AF 12-24mm f/4.5-5.6 EX DG 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, this may be it. 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 more pronounced 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. That all said there's also a weakness: lateral CAs at and below 17mm - you better use RAW files and correct the issue in your RAW converter. The principal build quality of the Sigma is excellent but watch out of sample variations (in terms of image quality).

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