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Lens review

Sigma A 40 mm f/1.4 DG HSM

10 December 2018
Maciej Lata³³o

4. Image resolution

The resolution test (resolution meaning MTF50 function) of the Sigma A 105 mm f/1.4 DG HSM was based on RAW files from the Canon EOS 5D Mark III. In the case of that reflex camera the decency level is situated near 30-32 lpmm and high quality, top-of-the-range fixed focal lenses can reach a maximum level of 45-50 lpmm . Not so long ago the resolution record for that sensor belonged to the Zeiss Otus 1.4/28 (49.2 lpmm) but then it’s been slightly beaten by the Sigma A 85 mm f/1.4 DG HSM, and the Sigma A 135 mm f/1.8 DG HSM so currently it amounts to 51.6 lpmm .

Let’s check how the Sigma A 40 mm f/1.4 DG HSM compares; its results in the frame centre and on the edge presents a graph shown below.

Sigma A 40 mm f/1.4 DG HSM - Image resolution

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When testing a lens like the Sigma you can’t help wondering whether or not it would reach a new resolution record. Officially the old one wasn’t broken because the maximum result of the new lens, reached by f/2.8, amounted to 49.8 lpmm - still a bit lower than the record of the Sigma A 1.8/135. On the other hand it is by 0.1 lpmm higher than the result of the former record holder, the Sigma A 1.4/85 so it would be difficult not to gush over the image sharpness provided by the tested lens.

As we are already talking about records, one of them was indeed broken but by the f/1.4 aperture. Not long ago we tested the Sigma A 105 mm f/1.4 DG HSM and that lens by f/1.4 achieved the highest result on full frame Canon and Nikon cameras in the history of our tests, amounting to 44.4 lpmm. The Sigma A 40 mm f/1.4 DG HSM reached 45.2 lpmm by the same aperture so a tad higher. Still it must be mentioned that taking measuring errors of 0.5–1.0 lpmm into account both these results are the same in the 1-sigma range.

The edge of the frame is equally impressive, if not more. Instead of describing every result in detail we focused on the performance at the maximum relative aperture. In that case on the edge of the APS-C/DX sensor the lens exceeds 44 lpmm and on the very demanding edge of full frame it reached almost 43 lpmm. Such performance means just one thing: with a very sensible angle of view, amounting to 57 degrees, the tested Sigma doesn’t have to be stopped down at all to achieve sensational sharpness across the frame.

Do you remember the cult Canon EF 135 mm f/2L USM? It’s been praised practically since forever because of its image quality; I admit I was entranced by its achievements myself when I finally got to test it. Still it’s worth comparing these results to the performance of a good contemporary lens. By f/4.0 the maximum resolution of the Canon in the frame centre amounted to 43.2 lpmm. The Sigma A 1.4/40 by f/1.4 fared the same, within the margin of error, but with one difference: it got to that value on the very edge of full frame…

Instead of summary let me show you a graph comparing the performance in the frame centre of the Sigma Art 1.4/35, 1.4/40 and 1.4/50. Do you need anything more?

Sigma A 40 mm f/1.4 DG HSM - Image resolution


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

Canon 5D MkIII, JPEG, 40 mm, f/1.4
Sigma A 40 mm f/1.4 DG HSM - Image resolution
Canon 5D MkIII, JPEG, 40 mm, f/2.8
Sigma A 40 mm f/1.4 DG HSM - Image resolution