Sigma A 20 mm f/1.4 DG DN review - Summary

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Sigma A 20 mm f/1.4 DG DN

5 October 2022

Maciej Latałło

11. Summary

Pros:

very solid, well-thought-out, weather-sealed mechanical construction,
very good image quality in the frame centre,
good image quality on the edge of the APS-C sensor,
sensible image quality on the edge of full frame,
negligible lateral chromatic aberration,
lack of coma-related problems,
slight astigmatism,
moderate vignetting on the APS-C sensor,
good performance of autofocus,
unique parameters,
possibility of using two types of filters.

Cons:

monstruous vignetting on full frame,
a tad too high longitudinal chromatic aberration.

It's very difficult to assess such lenses as the Sigma A 20 mm f/1.4 DG DN because they have no direct rivals. When it comes to this focal length Nikon and Sony offer you only slower devices. The only reference point is the predecessor of the tested Sigma designed for reflex cameras so the Sigma A 20 mm f/1.4 DG HSM but still any kind of comparison is not easy. When it comes the mirrorless version Sigma raised the bar significantly, deciding to offer a lens smaller, lighter, with a possibility of using classic 82 mm filters. As if it wasn't enough, you additionally got a possibility to use rear filters and many new functionalities on the barrel of the lens, e.g. The new MFL (Manual Focus Lock) switch, preventing an accidental focus change, and a part that allows you to attach heaters that might prevent condensation of dew on elements during nighttime shooting.

I didn't have any doubts that reduction of physical dimensions might adversely affect vignetting and indeed, we observed such a correlation. Vignetting is also the most serious Sigma's flaw but it hurts a bit less because it was completely expected. If the lens's bigger predecessor had a high level of vignetting, it would be foolish to count on a better performance in case of a smaller lens.

When it comes to resolution, the new Sigma performs more evenly than its predecessor and rivals. There are no resolution records in the centre but the results are evenly spread across the frame; as a result the Sigma is able to offer a sensible image quality in the whole of the frame, even at the maximum relative aperture. With such a wide field of view and such a great aperture fastness it is a huge achievement.

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There were also minor flaws, so moderate that we didn't bother to add them to our official 'cons' list. I suppose if distortion was corrected a tad better and spherical aberration was lower I would be completely happy with the lens.

Despite all these problems I don't doubt that the Sigma A 20 mm f/1.4 DG DN is a very well-put-together lens, a real step forward when comared to its reflex camera predecessor. There are categories where it fares a bit weaker than that instrument but there are also categories where it prevails, being a smaller, lighter, and far more functional lens overall.