Lens review

Sigma A 14-24 mm f/2.8 DG DN

23 December 2019
Arkadiusz Olech

4. Image resolution

The resolution test (resolution meaning MTF50 function value) of the Sigma A 14-24 mm f/2.8 DG DN was based on RAW files from the Sony A7R II. In the case of that mirrorless camera the decency level we set about 39-41 lpmm and some of the best fixed-focal lenses have been able to exceed 70 lpmm; so far the Samyang AF 85 mm f/1.4 FE (76.5 lpmm) and the Voigtlander Apo-Lanthar 65 mm f/2 Aspherical 1:2 Macro (78.5 lpmm) have fared the best.

Let's check how the Sigma A 14–24 mm f/2.8 DG DN compares – its results in the frame centre at 14, 19, and 24 mm focal lengths presents a graph below.

Sigma A 14-24 mm f/2.8 DG DN - Image resolution

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It is obvious at once that the lens's performance is not perfectly even but its results improve with the increase of the focal length. A similar effect was observed in the case of the Sigma A 14-24 mm f/2.8 DG HSM for reflex cameras although in its case the differences between 19 and 24 mm focal lengths were less pronounced. Still it's worth mentioning that the results of the tested instrument reached at all focal lengths are excellent already from the maximum relative aperture.

Of course the resolution performances of both Sigma lenses are difficult to compare directly because these instruments were tested on two different bodies. Still you can notice that in both cases the peak is reached near 91-93% of record level achieved by the best fixed-focal devices for a given detector. In conclusion you can say that, within the limit of measuring error, you deal here with two instruments which optical performances are excellent and very similar at the same time. Now let's check how the tested lens fares on the edge of the APS-C sensor – an appropriate graph can be found below.

Sigma A 14-24 mm f/2.8 DG DN - Image resolution

A curious thing: now the order of focal length results is reversed as the 14 mm focal length is the best and the 24 mm focal length – the worst. Still it should be noticed that the differences between 14 and 19 mm are not so pronounced and, in fact, they don't exceed limits of measuring error. What's more, already from the maximum relative aperture the MTFs exceed 50 lpmm so the quality of images remains beyond reproach.

What about the very demanding edge of full frame, especially with such parameters? Let's check it out!

Sigma A 14-24 mm f/2.8 DG DN - Image resolution

The changing of order between particular focal lengths continues because this time the middle of the range fares the best. The results at 14 and 24 mm are a bit weaker but they remain very similar; it is important, though, that even here at the maximum relative aperture the lens is able to reach 45 lpmm so a bit above the decency level. It is a better result than that of the Sigma A 14-24 mm f/2.8 DG HSM which, by f/2.8, landed below decency level at 24 mm and by f/4.0 at shorter focal lengths was barely able to exceed that value.

As you see, the producers managed to reach more balanced results across the frame with the mirrorless version of the lens, despite smaller dimensions and lower weight. The tested lens is able to fare better than the reflex camera model both on the edge of the APS-C sensor and on the edge of full frame. A round of applause!

At the end of this chapter, traditionally, we presents crops taken from photos of our resolution testing chart; they were saved in JPEG format along RAW files, used for the analysis presented above.

A7R II, JPEG, 14 mm, f/2.8
Sigma A 14-24 mm f/2.8 DG DN - Image resolution
A7R II, JPEG, 24 mm, f/4.0
Sigma A 14-24 mm f/2.8 DG DN - Image resolution