Lens review

Sigma A 20 mm f/1.4 DG DN

5 October 2022
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 or the Sony A7R III camera. 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 reach 75-80 lpmm, with record holders exceeding 80 lpmm. So far, the Voigtlander Apo Lanthar 50 mm f/2 E (81.0 lpmm), the Sigma C 65 mm f/2 GD DN (82.7 lpmm), and the Sony FE 20 mm f/1.8G (83.7 lpmm) have fared the best.

Let's check how the Sigma A 20 mm f/1.4 DG DN compares – its results in the frame centre and on edges of the APS-C sensor and full frame presents a graph below.

Sigma A 20 mm f/1.4 DG DN - Image resolution

The performance in the frame centre certainly would make any system prime device proud. Images are of good quality even at the maximum relative aperture and that quality improves very quickly on stopping down. Because of that, near f/4.0 the lens is able to achieve truly sensational level of almost 80 lpmm.

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Still, if you want to be fair you have to notice that its reflex camera predecessor deals better with resolution near the maximum relative aperture and the slower Sony FE 20 mm f/1.8G is even able to break resolution records. Before you start complaining seriously let's glance at the performance on the edge of the frame.

Interesting things happen here - the Sigma fares better than both its reflex camera predecessor and the rival Sony. It seems Sigma optics specialists didn't focus solely on the frame centre but also took care of a more ballanced performance all the time delivering you an impressive aperture fastness and a wide angle of view. As a result, the Sigma A 20 mm f/1.4 DG DN doesn't have any weak spots – even on the edge of the frame and at the maximum relative aperture it is able to produce completely useful images. Such a performance is out of reach of its heavier and bigger predecessor even though it comes with a huge front element, not limited by the size of front filters.

At the end of this chapter, traditionally, we present crops taken from photos of our resolution testing chart saved in JPEG format alongside RAW files which we used for the analysis above.

A7R III, JPEG, 20 mm, f/1.4
Sigma A 20 mm f/1.4 DG DN - Image resolution
A7R III, JPEG, 20 mm, f/4.0
Sigma A 20 mm f/1.4 DG DN - Image resolution