Sigma A 14-24 mm f/2.8 DG HSM review - Distortion

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Sigma A 14-24 mm f/2.8 DG HSM

9 April 2018

Arkadiusz Olech

6. Distortion

As long as the Sigma is attached to the smaller sensor Canon EOS 50D you won’t experience any serious distortion problems. You can notice them only at the shortest focal length where the distortion amounts to −1.46%. In the middle of the focal range its level drops to a value of −0.61%, and at the maximum focal length it decreases even further to −0.40%.

Canon 50D, 14 mm

Canon 50D, 19 mm

Canon 50D, 24 mm

On full frame the distortion is far more bothersome, especially at the 14 mm focal length where its barrel variant reached a level of −4.22%. Although that value is quite high, it remains lower than the result of the Tamron 15-30 mm at 15 mm (−5.81%).

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In the middle of the focal range the distortion becomes moderate, reaching −1.49%. At the maximum focal length you can even speak about a slight level of that aberration – officially we got a value of −0.73%.

Canon 5D III, 14 mm

Canon 5D III, 19 mm

Canon 5D III, 24 mm

In their official materials Sigma boast that the distortion level at the wide angle might drop to even −1%, but they emphasize the fact that they mean a result with the focus set at infinity. Our measurements show that the distortion level is much higher but, of course, it is hardly a secret that they don’t pertain to infinity. Our biggest chart for distortion measurement tests is a tad larger than the A0 format and still we have to position ultra-wide-angle lenses in a distance of less than one meter from it.

We came up with the following idea: we let the lens stay in such a distance that is necessary because of its focal length and the dimensions of the chart but we changed the position of the zoom ring. Setting the aperture by f/22 (as distortion doesn’t depend on the aperture value) at the 14 mm focal length you get the depth of field so vast that it doesn’t matter whether the ring is set at infinity or at 0.26 of a meter; the image of the chart remains sharp enough to make taking measurements possible. Our results are presented in the chart below. As the ring allows you to exceed the distance of 0.26 of a meter and the distance of infinity, we took measurements also for these places.

– – –

	Min.	0.26 m	0.30 m	0.40 m	0.60 m	1 m	~2 m	∞	over ∞
FF	–5.14%	−4.95%	–4.43%	–4.00%	–3.70%	–3.40%	−3.38%	−3.37%	−3.27%

As you see in this case the absolute distortion values have a distinct decreasing trend as the distance increase. However, even if the ring was set at infinity you still land far away from the −1% level.