Lens review

Sigma A 12-24 mm f/4 DG HSM

23 October 2016
Szymon Starczewski

4. Image resolution

The resolution test (resolution meaning MTF50 function) of the Sigma A 12–24 mm f/4 DG HSM was based on RAW files from the Canon EOS 5D Mark III. In the case of that reflex camera the decency level we situate near 30-32 lpmm and the best fixed focal length lenses have results reaching 45-48 lpmm. It’s worth mentioning here that not so long ago the resolution record on that sensor belonged to the Canon EF 35 mm f/1.4L USM II and it amounted to 48.0 lpmm but then came the Zeiss Otus 1.4/28 and it defeated the Canon setting a new record, that of 49.2 lpmm.

Still we are not interested by the results achieved by the primes in this category; the performance of the predecessor of the tested lens so the Sigma 12–24 mm f/4.5–5.6 II DG HSM and that of its direct rival, the Canon EF 11–24 mm f/4L USM is more important. Let’s remind here that the older Sigma provided similar resolution values at every focal length in the frame centre and it was completely useful already from the maximum relative aperture but without any spectacular achievements – its maximum MTFs reached about 35 lpmm. The Canon, on the other hand, was in a class on its own. Already at the maximum relative aperture it exceeded 40 lpmm and at the longer end of the focal range the MTFs got to almost 45 lpmm. The shortest focal length fared a bit weaker, with the maximum resolution reaching 43 lpmm.

Let’s check how the new Sigma compares – its results in the frame centre at 12, 18 and 24 mm are presented below.

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Sigma A 12-24 mm f/4 DG HSM - Image resolution

Firstly, it’s obvious the new Sigma is significantly better than its predecessor at practically every focal length. Secondly, its performance is opposite to that of the Canon; this time the best results you see at the shortest focal length where the lens is able to reach almost 44 lpmm, a splendid performance indeed. With the increase of the focal length the results worsen and the spherical aberration is to blame – next chapter is going to deal with that in more detail. Still even the longest focal length fares very well. Already at the maximum relative aperture the MTFs reach near 35 lpmm and they are able to exceed 40 lpmm on stopping down.

The edge of the APS-C sensor is weaker of course but, taking into account the angles of view offered by the lens, it still deserves to be praised.

Sigma A 12-24 mm f/4 DG HSM - Image resolution

First of all the new model outclasses the slower predecessor which, on stopping down, was able to reach barely about 30 lpmm. Here even at the weakest combination of the maximum relative aperture and the maximum focal length the lens is able to reach the decency level. It is obvious the constructors looked after the 12 mm focal length the most, assuming that the shorter end of the focal range is what users of such a lens care about and you have to admit the performance in that place is really brilliant. Already by f/4.0 the resolution exceeds 36 lpmm and on slight stopping down the lens is able to exceed a very high value of 40 lpmm - the Sigma at 12 mm is actually better than the Canon 11-24 mm at 11 mm.

Now let’s check the very demanding edge of full frame –the appropriate graph is shown below.

Sigma A 12-24 mm f/4 DG HSM - Image resolution

Once again the 12 mm focal length is the best – there are simply no weak points there. Even at the maximum relative aperture the image is sharp so the Sigma is able to defeat slightly the Canon. The middle of the focal range also doesn’t give you any reasons to complain – by f/4.0 and f/5.6 the lens is close to the decency level and by f/8.0 it reaches a good result, close to 35 lpmm. In this place, however, the new Sigma loses to the Canon because its focal range centre was actually the best on the edge of full frame. Also while examining the longest focal length you have something to complain about; only after employing f/6.3-f/7 apertures the images become useful.

To sum up the new Sigma is indeed better than its predecessor in every aspect; from time to time it is also able to compete successfully with the more expensive Canon EF 11-24 mm f/4L USM but, overall, it must be considered as a bit weaker in the resolution category despite its narrower focal range.

At the end of that chapter traditionally we present crops taken from photos of our resolution testing chart which were saved as JPEG files.

Canon 5D MkIII, JPEG, 12 mm, f/5.6
Sigma A 12-24 mm f/4 DG HSM - Image resolution
Canon 5D MkIII, JPEG, 24 mm, f/4.0
Sigma A 12-24 mm f/4 DG HSM - Image resolution