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Sigma C 16-28 mm f/2.8 DG DN – first impressions

1 June 2022
Maciej Latałło

3. Autofocus and some remarks concerning optical properties

Some pieces of good news first – sample shots, published in the last chapter, don't feature anything disturbing. The lens seems to perform evenly, without any focal length sticking out or lagging behind the rest. What's more, even by f/2.8 photographs are decently sharp. I admit our expectations before the full test of the production specimen are really high now.

The optical construction of the Sigma features low dispersion glass elements and that fact suggests there shouldn't be any problems with longitudinal chromatic aberration. The photo below confirms that much.

A7R III, 28 mm, f/2.8
Sigma C 16-28 mm f/2.8 DG DN – first impressions - Autofocus and some remarks concerning optical properties



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Despite a complex optical construction, internal focusing, and a significantly big front element that is not hidden very deep inside the casing, we didn't notice any serious problems with the performance against brigh light - an interesting and praiseworthy feature. A sample shot taken at a very difficult combination of the widest angle of view and an aperture of f/8.0, with the sun inside the frame, proves that much – you can catch some weak light artifacts but they are few and far between and their intensity is low. What's more, the photos don't show any distinct contrast loss.

Sigma C 16-28 mm f/2.8 DG DN – first impressions - Autofocus and some remarks concerning optical properties

The Contemporary series has made us used to the fact that constructors give up on distortion and vignetting correction, pinning it on the software of the camera. Also this time we didn't expect any good results in these categories and ideed, we weren't positively surprised. Distortion at 16 mm is distinct, its average level amounting to near -5.4% across the frame. What's worse, it has been reduced by introducing moustache distortion. As a result, if you limit your measurements to the area of 1:1 markings that aberration can increase to -6.3%. It's a lot.

Unfortunately, the maximum focal length is not completely distortion-free either but this time deformations are of pincushion variety and reach +2.9%.

Sony A7R III, 16 mm, JPEG
Sigma C 16-28 mm f/2.8 DG DN – first impressions - Autofocus and some remarks concerning optical properties
Sony A7R III, 70 mm, JPEG
Sigma C 16-28 mm f/2.8 DG DN – first impressions - Autofocus and some remarks concerning optical properties


In case of vignetting you can spot a lot of problems at the most difficult combination of the 16 mm focal length and the maximum relative aperture. Here brightness loss in the frame corners increase to a very high level of almost 75% (około 4 EV). As the focal length increases, the vignetting decreases – at 28 mm and by f/2.8 it amounts to 55% (about -2.3 EV).

A7R III, FF, 16 mm, f/2.8 A7R III, FF, 28 mm, f/2.8
Sigma C 16-28 mm f/2.8 DG DN – first impressions - Autofocus and some remarks concerning optical properties Sigma C 16-28 mm f/2.8 DG DN – first impressions - Autofocus and some remarks concerning optical properties


We had an opportunity to attach the Sigma C 16-28 mm f/2.8 DG DN to the Sony A7R III camera. Such a set worked noiselessy and was pretty quick – running through the whole distance range and confirming the focus took about 0.5 of a second. There was no serious wavering, a delicate going in and out of focus could be observed near the very end of the range, close to the right aim. Overall we don't have any serious reservations here and we assess the performance of the focusing mechanism rather high. Of course you should remember that we handled a specimen with a pre-production software so the autofocus unit might be improved in the final version of the lens.