Sigma C 50 mm f/2 DG DN
5. Chromatic and spherical aberration
Chromatic aberration
The Sigma 2/50 has just one element made of low dispersion SLD glass and, it seems, it's not enough to eliminate longitudinal chromatic aberration completely. Its influence is visible – images before the focus have slight red colouring and those behind the focus are green-blue. Fortunately it's not a very serious or even moderately serious flaw and it shouldn't bother you in most of settings. |
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What about lateral chromatic aberration? Let's glance at a graph below and find out.
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Here, for a change, there are no reasons to complain. This aberration doesn't depend strongly on aperture values and never exceeds 0.04% on edges of both types of detectors. In our tests such a result is considered to be on the borderline of very low and low levels, nothing to worry about.
| A7R III, RAW, f/2.0 | A7R III, RAW, f/5.6 |
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Spherical aberration
The tested lens is free from any noticeable 'focus shift' effect or slightly 'misty' images at the maximum relative aperture, both being characteristic features for badly corrected spherical aberration. Defocused circles of light we got before and behind the focus didn't show anything disturbing. All these findings make us think that the Sigma C 50 mm f/2 DG DN corrects spherical aberration pretty well.
| A7R III, f/2.0, before | A7R III, f/2.0, after |
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