Sigma C 90 mm f/2.8 DG DN – first impressions and sample images - Autofocus and some remarks concerning optical properties

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Sigma C 90 mm f/2.8 DG DN – first impressions and sample images

9 September 2021

Maciej Latałło

3. Autofocus and some remarks concerning optical properties

The last chapter of this article features sample shots we took with the pre-production Sigma C 90 mm f/2.8 DG DN. It is clear that you deal here with a very sharp lens that provides at least good image quality up from the maximum relative aperture. Perhaps this one won't break any resolution records but only because it is limited by its maximum aperture and resolution records are most often set by lenses faster than f/2.8.

The autofocus of the Sigma C 2.8/90 combined with the Sony A7R III is completely noiseless but it can't be called very fast. Running through its distance range and confirming the right position takes about 0.6-0.9 of a second and it seems the lens is a tad faster when moving towards smaller distances. When you go from the minimum focusing distance to infinity sometimes you can encounter untypical problems – the mechanism can stop too early and it finds the right position only after pressing the shutter release once again.

Still, you should remember that we deal here with a pre-production model; many things concerning the performance of the autofocus can be fine-tuned before the launch. We hope the autofocus of the final version of the lens will be far more efficient.

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Performance against bright light is another feature easy to correct even in the last production stages – you can always modify slightly the coatings, blacken the interior better, add apertures, and internal baffles. Such treatment would be highly advisable in case of the Sigma C 2.8/90 because you can catch some flares with it. Still it should be admitted that, with this focal length, you will get few occasions to put the sun inside the frame or close to one of its corners.

Sigma C 90 mm f/2.8 DG DN – first impressions and sample images - Autofocus and some remarks concerning optical properties

The lens is relatively small so vignetting might be also a problematic area. After a cursory look we think that the situation is not very bad, with distortion never exceeding 3 EV. Still, we must emphasize the fact that in the case of the Contemporary series instruments Sigma optics specialists have a clear list of priorities - first come image quality, sensible dimensions, and a moderate price tag. These three things have to be achieved even if they have to pay for them with higher vignetting and distortion. After all, these two aberrations are the easiest to correct with a camera's software.

As we've already mentioned distortion – the Sigma C 90 mm f/2.8 DG DN is not completely free from that aberration because you can spot pincushion deformations in the photos without any problems. Currently we cannot estimate their precise values but after a full test of one of the Sigma production specimens we will be able to say more.