Lens review

Sigma C 56 mm f/1.4 DC DN

22 December 2018
Arkadiusz Olech

4. Image resolution

As the Sigma C 56 mm f/1.4 DC DN is a lens designed to cover the APS-C sensor we decided to check its resolution with the help of the Sony A7R II set in the APS-C mode. If the APS-C sensor results are expressed in lpmm (so exactly like in our tests) they can be directly compared to results of full frame lenses tested with the help of this camera. In the case of this mirrorless lens the decency level is situated around 39-41 lpmm and the best fixed-focal lenses can reach as high as 70 lpmm. So far the record values have been achieved by the Tokina Fírin 20 mm f/2 FE MF (72.6 lpmm) and Voigtlander Apo-Lanthar 65 mm f/2 Aspherical 1:2 Macro together with the Sigma C 16 mm f/1.4 DC DN (78.5 lpmm).

Let’s check how the new Sony E mount Sigma C 56 mm f/1.4 DC DN compares.

Sigma C 56 mm f/1.4 DC DN - Image resolution

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When it comes to the frame centre our first question is: how do they do it? I start testing new mount version lenses. I take models produced by different companies, as renowned and famous for excellent optics quality as Zeiss. I check the maximum resolution their optics is able to generate on a given sensor and when it seems that these maximum results are well-defined and known for good here it comes, the cheap Sigma C 16 mm f/1.4 DC DN and, surprise, surprise, it reaches the record values without any problems. Then I test equally cheap Sigma C 56 mm f/1.4 DC DN and it fares even better, breaking the previous resolution record by several lpmm and setting its own at 82.4 lpmm. Mind you its image quality is excellent already from the maximum relative aperture.

Still, in order to be honest, I have to mention the price you have to pay for it. The ‘Contemporary’ series is limited by dimensions and price tags, making the task of optics constructors really difficult. They had to compromise and they sacrificed the performance on the very untypical edge of the frame.

That edge of the frame doesn’t provide bad images – even at the maximum relative aperture you still are above the decency level. Still we don’t like how the resolution depends on the aperture value as there is a significant dip by f/2.8. It is not a measuring error because that effect was visible on all our testing charts. Its existence is additionally confirmed by local maximum of some aberrations, visible exactly by f/2.8. You should sensibly assume it is one of the costs you have to pay for frame centre resolution records, especially that similar decrease of resolution near f/2.8 featured also the Sigma C 1.4/16.

At the end of this chapter, traditionally, we presents crops taken from photos of our resolution testing chart saved as JPEG files along with RAW files used for the analysis above.

Sony A7R II, JPEG, f/1.4
Sigma C 56 mm f/1.4 DC DN - Image resolution
Sony A7R II, JPEG, f/2.8
Sigma C 56 mm f/1.4 DC DN - Image resolution