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 – Image quality
What with our review sample of the lens arriving in Canon-fit and being designed for today’s era of ultra-high-resolution cameras, it seemed sensible to pair it up with one of Canon’s 50-million-pixel DSLRs – the EOS 5DS R. Eager to first find out just how well the lens performs with regard to controlling curvilinear distortion, I headed out to take a series of real-world sample images throughout the focal range before examining these alongside the images of our distortion chart that were taken in the lab.
Creating such an ultra-wideangle lens with zero distortion was always going to be a big ask, and although there’s virtually no distortion between the focal lengths of 18mm and 24mm, you can still expect to see barrel distortion in shots taken at the widest end of the zoom. That being said, the severity of barrel distortion at 12mm isn’t as severe as you might expect and shouldn’t be difficult to correct using an Adobe lens profile as soon as one becomes available for Lightroom CC, Photoshop CC and Camera Raw. All being well, we’ll see the lens supported, along with the Sigma 500mm f/4 DG OS HSM and 85mm f/1.4 DG HSM Art in Adobe’s next Creative Cloud update.
Analysing our Applied Imaging tests at each aperture setting revealed that the lens resolves an exceptional level of sharpness. Our results tell us the lens is at its sharpest in the centre at the widest end of the focal length, with corner sharpness at 12mm peaking at f/8. Zooming in to 18mm also sees the corner sharpness peak at f/8, with the centre sharpness at this focal length measuring slightly below the figure we recorded at 12mm at f/4.
Inspecting our results at the long end of the zoom tells us the centre sharpness isn’t quite as impressive as it is at the wide end when it’s used wide open (f/4), but sharpness does improve by closing the lens down to f/5.6. The best sharpness at the edge of the frame at 24mm is recorded between f/8 and f/11. Overall, the sweet spot between centre and corner sharpness is found between f/5.6 and f/8. The lens continues to resolve sharp results beyond these settings up to f/11, but diffraction does start to play a role in softening images as you close down to f/16 and f/22.
Examining the edges, where chromatic aberrations can often be discovered, revealed that the lens does an admirable job of keeping fringing in check. It was only in the very brightest areas of a few of my test shots, where branches were backlit by the sun, that I noticed some purple fringes of colour. Vignetting is apparent in images shot at the widest end of the zoom at f/4, but clears up as you close down to f/5.6 and beyond. The same is said of the long end of the zoom where corners appear approximately 1.2EV darker than the centre at f/4.