LensTip.com

Lens review

Sigma C 20 mm f/2 DG DN

5 July 2022
Maciej Latałło

8. Vignetting

First let's check vignetting on the smaller APS-C sensor – appropriate thumbnails are shown below.

A7R III, APS-C, f/2.0 A7R III, APS-C, f/2.8
Sigma C 20 mm f/2 DG DN - Vignetting Sigma C 20 mm f/2 DG DN - Vignetting


In this case you can spot vignetting only at the maximum relative aperture, where it amounts to 30% (−1.03 EV). By f/2.8 the aberration decreases to 17% (−0.52 EV), and by f/4.0 it drops to 14% (−0.44 EV)


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After passing to the full frame sensor there are far more problems; images, presented below, show it pretty clearly.

A7R III, FF, f/2.0 A7R III, FF, f/2.8
Sigma C 20 mm f/2 DG DN - Vignetting Sigma C 20 mm f/2 DG DN - Vignetting
A7R III, FF, f/4.0 A7R III, FF, f/5.6
Sigma C 20 mm f/2 DG DN - Vignetting Sigma C 20 mm f/2 DG DN - Vignetting


At the maximum relative aperture vignetting reaches a monstrous level of 77% (−4.27 EV). I am always irritated when, with such a high vignetting level, somebody suggests the lens in question should be considered slower than declared by the producer. In this case, however, I think Sigma went over the top; indeed they should have made this lens slower aperture-wise or maybe simply a tad bigger. That way they would have avoided such a serious slip-up.

Vignetting remains on a very high level also after stopping down the aperture: by f/2.8 you get a level of 66% (−3.08 EV), by f/4.0 it reaches 52% (−2.10 EV), and by f/5.6 the result amounts to 40% (−1.48 EV). Further stopping down doesn't cause any measureable decrease of this aberration.

Sony A7R III, JPEG, f/2.0
Sigma C 20 mm f/2 DG DN - Vignetting