Sigma A 17-40 mm f/1.8 DC review - Image resolution

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Sigma A 17-40 mm f/1.8 DC

25 August 2025

Maciej Latałło

4. Image resolution

Our resolution test (resolution meaning the MTF50 function values) of Sony FE lenses is based on RAW files from the 42.4 Mpix sensor of the Sony A7R II, the Sony A7R III or the Sony A7R IIIa cameras. In the case of this kind of detector the decency level we set about 39-41 lpmm and the best fixed focal length lenses have been able to exceed 80 lpmm. Record-breaking lenses are able to go beyond 85 lpmm or even 90 lpmm and so far, our list of these record-breakers features the Viltrox AF 85 mm f/1.4 Pro (85.9 lpmm), the Meike 85 mm f/1.4 FF STM (90.2 lpmm), and the Sony FE 50 mm f/1.4 GM (90.9 lpmm).

Let's check how the Sigma A 17-40 mm f/1.8 DC compares with its frame centre results.

Sigma A 17-40 mm f/1.8 DC - Image resolution

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You can say at once that the results are simply sensational. Not so long ago we changed our lists of record-breakers, adding to it the Sigma A 28-45 mm f/1.8 DG DN, mentioned by us in the introduction to this test. Soon the Viltrox AF 85 mm f/1.4 Pro managed to replace it on the podium but now we can announce that another lens of Sigma is back, with the result of 89.9 +/- 0.4 lpmm reached at 17 mm focal length and f/2.8 aperture. The fact that the podium would belong to it also with the result of 89.6 +\- 0.4 lpmm reached at 28 mm and by f/2.8 is also important.

The 40 mm focal length is officially the weakest but in fact it fares sensationally well, with a result of 85.4 +\- 0.9 lpmm, within the margin of measuring error practically the same as the result of the Viltrox AF 85 mm f/1.4 Pro that is being knocked off the podium.

What about the edge of the APS-C/DX? Are the result going to be equally brilliant? Let's glance at a graph below and check it out.

Unfortunately, here you don't see such an even performance. The middle of the focal range fares the best, with really excellent values, not limited by chromatic aberration (and details are going to be provided in the next chapter). To be honest such performance as the tested Sigma shows on the edge wouldn't shame even a good prime.

In case of both ends of the focal spectrum the chromatic aberration makes itself felt noticeably stronger, its specific performance shaping the resolution graph in a specific way, especially at the shortest focal length. The initial stopping down of the aperture causes even a slight decrease of the resolution. However, the 17 mm and 40 mm focal lengths present a very similar, quite flat resolution graph with very good results, bordering 60 lpmm for a wide range of apertures from f/1.8 to f/8.0. In case of such extreme parameters it's definitely more than you might expect.

To sum up the unique Sigma A 17-40 mm f/1.8 DC not only has no weak points, but also practically at all focal lengths managed to attack the podium with its superior resolution. We find its performance in this category simply beyond reproach. At the end of this chapter, traditionally, we present crops taken from photos of our resolution testing chart; they were saved as JPEG files along RAW files, used for the analysis above.

A7R IIIa, JPEG, 17 mm, f/2.8