Sigma C 16 mm f/1.4 DC DN
5. Chromatic and spherical aberration
Chromatic aberration
Unfortunately the Sigma cannot be praised for the correction of longitudinal chromatic aberration. Its level was clearly visible even after stopping down the aperture to f/2.0, no matter what camera you attached the tested lens to. |
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The situation with the lateral variety of that aberration was better – a graph below presents the results correlative with the detector used and the aperture value.
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Most of values range from 0.05-0.07% so they are low. It means that lateral chromatic aberration shouldn’t be bothersome in real life photos.
| Olympus E-M5 II, RAW, f/2.8 | Sony A7R II, RAW, f/2.8 |
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Spherical aberration
Not entirely corrected spherical aberration might be the cause of less-than-impressive Sigma performance by f/1.4. We saw a slight “focus shift” effect while testing the lens on both bodies; also circles of light, shown below, produced in front of and behind the focus, are a classic example of that aberration. The circles before the focus are soft on edges and those after the focus feature a lighter rim. It is not a very distinct effect (its level is a bit higher with the lens attached to the Olympus and a bit lower when the lens cooperates with the Sony) but you can hardly call this degree of spherical aberration correction good.
| Olympus E-M5 II, f/1.4, in front of | Olympus E-M5 II, f/1.4, behind |
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| Sony A7R II, f/1.4, in front of | Sony A7R II, f/1.4, behind |
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