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Sigma AF 12-24mm f/4.5-5.6 EX DG - Review / Lab Test Report - Analysis |
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Lens Reviews -
Sony Alpha/NEX (APS-C)
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Thursday, 28 February 2008 11:58 |
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Page 2 of 2
Distortions
The Sigma shows a very seldom distortion characteristic for an ultra-wide angle
lens - it is extremely well corrected here with very low barrel distortions even
at 12mm. The lens is basically free of distortions at 24mm.
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Move the mouse cursor over the focal length text marks below to observe the respective distortions
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| 12mm |
17mm |
24mm |
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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 in line widths per picture height (LW/PH)
which can be taken as a measure for sharpness. If you want to know more about it 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.
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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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