Sigma A 24-105 mm f/4 DG OS HSM
5. Chromatic and spherical aberration
Chromatic aberration
The Sigma 24-105 mm corrects the longitudinal chromatic aberration very well. If you look at the blurred areas it’s hard to notice any distinct cast - the lens should be praised for it.
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The situation with the lateral chromatic aberration is a bit different though; that aberration makes itself distinctly felt on the APS-C/DX sensor (the first of the graphs, presented below) and on the edge of full frame (the second graph).
At the shortest focal length and near the maximum relative aperture the chromatic aberration level is high. In the case of bigger focal lengths the correlation between the chromatic aberration and the aperture values is poor so its level is medium, from time to time approaching high.
In this category the Sigma loses noticeably to the Canon 24-105L which was better at every focal length. The Nikkor didn’t fare especially well in this category because near the maximum relative aperture it had an aberration level exceeding a very high value of 0.2%. Still in its case the stopping down helped a lot – that’s why near f/11 the results of the Sigma and the Nikkor are comparable.
Here the order seems to be clear: the Canon is the best, the second place goes to the Sigma and the Nikkor is the worst of all.
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Spherical aberration
The spherical aberration level of the Sigma 24-105 mm is not high but still remains noticeable. A slight focus shift can be seen even in the first photo of this chapter. By f/4.0 the sharp areas in front of the focus are bigger and on stopping down to f/5.6 the depth shifts towards the longer end. The effect is not big and it can be noticed only when employing extreme settings but it shows that this aberration hasn’t been contained completely.
The appearance of defocused light circles confirm that much. Both show a series of small local extremes which change the sign when you move from one side of the focus to the other.
