Michael Topham puts Sigma’s latest wideangle zoom to the test and finds out if it lives up to the promise of producing zero distortion
Sigma 12-24mm f/4 DG HSM Art review – Resolution, shading and curvilinear distortion
Our Applied Imaging tests indicate that the lens is at its sharpest in the centre towards the widest end of the focal length. It’s exceptionally sharp when it’s used wide open (f/4) at 12mm and the chart tells us the centre improves at 24mm when the aperture is closed down towards f/5.6. Users will find they’ll record the finest edge-to-edge sharpness across the frame between f/5.6-f/8, which is standard for a full-frame lens. Great results can be achieved by closing the lens down to f/11, although you’ll notice that diffraction does play its part in softening images as you close down to f/16 and f/22.
Shoot at the widest end of the zoom (12mm) with an aperture of f/4 and your images will feature vignetting. However, it’s not as severe as you might expect in a lens so wide. Corner shading quickly disappears at 12mm as you start to close the lens down to f/5.6. Edges are approximately 1.2EV darker than the centre at 24mm, but again this corner shading improves by stopping down to f/5.6. It can’t be traced at all at f/8 or beyond.
Subjecting the lens to our distortion chart shows that straight lines bow outward from the centre of the image at 12mm. This barrel distortion isn’t as severe as some ultra-wideangle lenses and you’ll notice it becomes less recognisable when you zoom in slightly. At 18mm, there’s no trace of distortion whatsoever and there’s only a faint sign of pincushion distortion when you push to 24mm. Considering just how wide the lens is, this is a very impressive curvilinear distortion performance.