Sigma A 24-70 mm f/2.8 DG DN review - Distortion

Have you rated your lenses yet?

Sigma A 24-70 mm f/2.8 DG DN

22 January 2020

Arkadiusz Olech

6. Distortion

Distortion correction cannot be counted among the strengths of the tested Sigma – it remains clearly visible even on the APS-C sensor. At 24 mm you have to tackle significant barrel variation of that aberration, amounting to −3.46% (that high value we are going to explain in a moment). After increasing of the focal length to 35 mm deformations decrease to −0.82% and then they change the sign. As a result at 50 mm you already deal with slight 'pincushion' of +0.22% and it increases to +0.60% on passing to the maximum focal length.

One glance at the photo of our testing chart, taken on full frame, explains why we can't say anything favourable about distortion correction of the Sigma 24-70 mm and why its level is so high on the APS-C sensor. You deal here with a nasty case of moustache distortion, very difficult to correct. Officially our measurement amounts to −4.56% when averaged out across the frame so it might seem nothing especially worrisome, just a tad higher than the value we measured for the smaller detector. Still, when you limit your measurments to the 1:1 markings area you can observe the problem in all its glory. Distortion is as high as −6.47%; what's more, traces of that aberration can be observed even at 35 mm. At that point the official distortion level is just −0.89%, but that value is reduced by a slight bending of lines on the edges caused by the aferomentioned „moustaches”.

At 50 and 70 mm there are far less problems with the results as follows:+0.94% and +1.32%.

Please Support Us

If you enjoy our reviews and articles, and you want us to continue our work please, support our website by donating through PayPal. The funds are going to be used for paying our editorial team, renting servers, and equipping our testing studio; only that way we will be able to continue providing you interesting content for free.

- - - - - - - - - - - - - - - - - advertisement - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

We don't exactly like the performance of the Sigma in distortion category. We understand that it's an aberration that might be left uncorrected because software deals with it efficiently; still that fact remains true only when its level is not especially high and it doesn't concern mounstache distortion too. When distortion results are high you have to crop the field of view after the correction. What's more, while barrel distortion is easy to correct, its moustache version remains a far trickier issue.

It's worth reminding here that the reflex camera Sigma A 24-70 mm f/2.8 DG OS HSM also esperienced problems with moustache distortion which was visible from 24 mm up to 35 mm. Still those levels were distinctly lower – the result across the frame at 24 mm reached −3.31%, and in the 1:1 markings area it approached −4.19%. You have to admit there is a huge difference between −4.19% and −6.47%.