Lens review

Sigma A 14 mm f/1.8 DG HSM

14 July 2017
Maciej Latałło

4. Image resolution

The resolution test (resolution meaning here MTF50 function values) of the Sigma A 14 mm f/1.8 DG HSM was based on RAW files from the Canon EOS 5D Mark III. In the case of that reflex camera the decency level is situated near 30-32 lpmm and the best fixed-focal lenses can reach as high as 45-49 lpmm. It’s worth adding that the resolution record on that sensor not so long ago belonged to the Zeiss Otus 1.4/28 (49.2 lpmm) but was lately bested by the Sigma A 85 mm f/1.4 DG HSM and then the Sigma A 135 mm f/1.8 DG HSM; currently it amounts to 51.6 lpmm

Let’s check how another prime produced by Sigma compares here – its result in the frame centre, on the edge of the APS-C/DX sensor and on the edge of full frame presents the graph below.

Sigma A 14 mm f/1.8 DG HSM - Image resolution

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The frame centre is similar to the results we have seen in tests of any other Art series prime devices. Already at the maximum relative aperture the MTFs reach 42 lpmm and on stopping down they even increase to a peak of over 47 lpmm by f/4.0. It is a level practically identical to those of other Art series lenses we praised so much (maximum results of 47 lpmm got also e.g. the 1.4/20, the 1.4/35 and the 1.4/50 models).

What’s interesting the best value the Sigma got in this category is just slightly higher than the result of the Samyang 14 mm f/2.8 ED AS IF UMC but noticeably better than the result of the Irix 15 mm f/2.4 Blackstone

The edge of the APS-C/DX sensor seems to be beyond reproach. With such extreme parameters the producers still managed to guarantee good image quality right from the maximum relative aperture. Mind you, the competition in that segment is fierce. Even though the Sigma fares the best near f/2.8 because it is the fastest and, on stopping down to f/1.8, its optical aberrations are noticeably limited, on further stopping down the Samyang 2.8/14 and the Irix 2.4/15 can actually reach higher resolution levels – the Samyang gets to 40 lpmm and the Irix can even exceed that value slightly. The maximum result of the Sigma is less than 39 lpmm. As you see the values differ just slightly, being almost on a borderline of measuring error levels but, officially, the Sigma is the weakest at that point.

The performance on the edge of full frame shows that the Samyang is really a very serious rival. The Irix fared the weakest here although, because of the narrowest angle of view, its task was also the easiest. The Samyang, though, already near its maximum relative aperture (f/2.8) brushed against the usefulness level. The faster Sigma has to be closed down to near f/4.0 in order to achieve that much. Instead that lens provides the best image quality in that part of the frame because on even more pronounced stopping down it reaches over 34 lpmm. The peaks of the Samyang and the Irix were by several lpmm lower.

It’s also worth mentioning that the Canon EF 14 mm f/2.8L USM II, even if the most expensive in this group, was the weakest on the edge of the frame even if it could defend itself well in the frame centre.

To sum up this chapter I can write without any hesitation that the Sigma A 14 mm f/1.8 confirmed the high quality of Art line lenses. It was very difficult, to guarantee a sensational image quality in the frame centre up from the maximum relative aperture, but the Sigma carried out its task to perfection. Of course you can wonder whether the performance on the edge of full frame could have been a bit better but the lack of direct rivals and appropriate material for comparisons makes it difficult to draw any binding conclusions.

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

Canon 5D MkIII, JPEG, 14 mm, f/1.8
Sigma A 14 mm f/1.8 DG HSM - Image resolution
Canon 5D MkIII, JPEG, 14 mm, f/4.0
Sigma A 14 mm f/1.8 DG HSM - Image resolution