Sigma A 28-45 mm f/1.8 DG DN review

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Sigma A 28-45 mm f/1.8 DG DN

27 September 2024

Maciej Latałło

5. Chromatic and spherical aberration

Chromatic aberration

In a f/1.8 lens with such a focal range the correction of longitudinal chromatic aberration was certainly not an easy task. Still Sigma managed it quite well and photos, shown below, are the proof. Even at the maximum relative aperture it's difficult to notice any out-of-focus colouring and it means that the lens corrects this aberration in a proper way.

Sigma A 28-45 mm f/1.8 DG DN - Chromatic and spherical aberration

Let's check now the situation with the correction of lateral chromatic aberration – two graphs below, one for the edge of the APS-C sensor and the other for the edge of full frame, present its performance depending on focal length and aperture values.

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It is clear that the longer focal lengths are corrected very well. We got results ranging from 0.03 to 0.04% so on the borderline between imperceptible and low level.

A bit bigger problems can be observed at the widest angle of view. Here you deal with a quite flat run and the values hover around 0.10-0.11%, a medium level that sometimes can be spotted in real life photos. It would be difficult to call it a serious flaw but it is the first small scratch in otherwise pristine performance of the Sigma A 28-45 mm f/1.8 DG DN.

A7R IIIa, RAW, 28 mm, f/1.8	A7R IIIa, RAW, 36 mm, f/4.0

Spherical aberration

Even after a closer look it would be difficult to notice any focus shift effect in first photos from this chapter. Some traces of less-than-perfect correction of spherical aberration are noticeable in circles of light we got before and behind the focus. In the first case you see soft edges and in the other – a brighter rim. The effect, being not especially strong, remains visible on both ends of the focal range.

The problems with spherical aberration are accented but the optics constructors cared more about nice appearance of out-of-focus areas. Lack of any focus shift and a very good quality of images by f/1.8 allow us to think that in this lens spherical aberration is properly curbed.