Sigma has created a world first with its latest wideangle prime lens, but how valuable is it in the company’s line-up? Michael Topham investigates
Sigma 20mm f/1.4 DG HSM | A Review – Image quality
Our review sample was supplied in Canon-fit, and for testing purposes I paired it with the Canon EOS 5DS. Given the highly impressive level of detail this camera resolves, I wanted to find out whether or not its results wide open are as impressive as those we’ve seen from Sigma’s other Art lenses in the past.
Rattling off a series of frames of the same scene from f/1.4 to f/16 and then analysing these alongside our Applied Imaging tests revealed a jaw-dropping set of results. Sharpness in the centre of the frame at f/1.4 is very impressive. Edge sharpness is a little way off matching the same level of sharpness in the centre at f/1.4, so to record the finest level of edge-to-edge sharpness across the frame you’ll need to close the lens down a few stops. Corner sharpness improves by the time you reach f/4, but the sweet spot between centre and corner sharpness is located closer to f/5.6-f/8. The lens continues to resolve sharp images beyond these settings and f/11 is certainly usable if you’re keen on creating a larger depth of field. Diffraction does begin to soften images a little at f/16, so it’s good to see Sigma putting a cap on the lens’s minimum aperture.
Equally as impressive is the way this lens controls curvilinear distortion. Although it’s not entirely distortion-free, the barrel distortion it does exhibit is negligible and can’t easily be traced in shots straight out of the camera. I did notice some signs of purple and green fringing at the edges of the opening image to this review, but that was only obvious at very close magnification. At the time of testing we were still awaiting a new lens profile update from Adobe. When this does become available we expect these signs of chromatic aberration and barrel distortion to be resolved with a single click of the ‘Enable Profile Corrections’ box beneath the Lens Corrections tab.
The corners are around 2EV darker than the centre of the image when the lens is used at f/1.4. Closing the lens down to f/2 sees corner shading improve and dialling in an aperture of f/3.2 sees vignetting clear up almost completely. It’s untraceable in images that are taken at and beyond f/4.