Sigma has a superb selection of wide-angle primes. Michael Topham reviews the latest addition
Sigma 28mm F1.4 DG HSM Art review: Resolution, shading and curvilinear distortion
Our Image Engineering MTF tests were carried out with the lens coupled to Canon’s 50-million-pixel DSLR, the EOS 5DS R. The solid red line shows that there’s an improvement when you stop down from the maximum aperture, with centre sharpness peaking around f/4. Corner sharpness peaks slightly later in the aperture range and to find the sweet spot of edge-to-edge sharpness users will want to use the lens at f/5.6. Push beyond f/8 to f/11 or f/16 and you’ll begin to notice softening from diffraction.
Shoot wide open at f/1.4 and you’ll be able to make out gradual vignetting at the edge, which measures approximately 1.7EV darker than the centre of the frame. Stop down to f/2 and you’ll find it reduces considerably, and by f/2.8 it’s essentially gone altogether. If the vignetting at large apertures disturbs you, it can be fixed in post-processing using programs such as Adobe Lightroom or DxO Optics Pro.
The results from our distortion tests reveal that the lens does exhibit barrel distortion, however it’s well controlled and crucially doesn’t drop below a figure of -1.0 TV SMIA [%]. The recorded figure (-0.9 TV SMIA [%]) isn’t quite as impressive as the the Sigma 24mm F1.4 DG HSM Art (-0.7 TV SMIA [%]), however you’ll find that the barrel distortion is barely visible in real-world images.