Sigma A 40 mm f/1.4 DG HSM review - Chromatic and spherical aberration

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Sigma A 40 mm f/1.4 DG HSM

10 December 2018

Arkadiusz Olech

5. Chromatic and spherical aberration

Chromatic aberration

The tested lens doesn’t have practically any problems with the longitudinal chromatic aberration. Even at the maximum relative aperture and in out-of-focus areas positioned in some distance it is difficult to notice any tint. It seems all these six low dispersion elements included in the Sigma optical construction perform as they should.

Sigma A 40 mm f/1.4 DG HSM - Chromatic and spherical aberration

The lateral chromatic aberration can be described in similar terms – the graph with the performance on both types of detectors we present below.

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Practically all results we got are close to 0.03%, a level we consider to be very low. The Sigma A 1.4/40 won’t cause you any problems when it comes to any variation of chromatic aberration.

Canon 5D III, RAW, f/1.4	Canon 5D III, RAW, f/8.0

Spherical aberration

First photos of this chapter show a noticeable focus shift – when you pass from f/1.4 to f/2.0 and then to f/2.8 the depth of field moves toward the back. It means the Sigma doesn’t correct spherical aberration in a perfect way. In order to check how serious the problem really is we performed another test, an assessment of defocused circles of light reached before and after the focus.

Canon 5D III, f/1.4, in front of	Canon 5D III, f/1.4, behind

The influence of spherical aberration is visible here as well – the circle we got before the focal point has soft edges and its brightness decreases when you move toward the edge. The circle from the other side of the focus features a distinctly lighter rim for a change. It is another classic symptom of spherical aberration.