Sigma’s third f/1.4 prime lens for Sony E and Micro Four Thirds mounts has arrived. Michael Topham offers his verdict
Sigma 56mm f/1.4 DC DN Contemporary review: Resolution, shading and curvilinear distortion
A study of our Image Engineering Tests reveals the lens is sharper in the centre than at the edge throughout the aperture range. Centre sharpness (shown by the solid red line) improves considerably by stopping it down from its maximum aperture to f/2 and peaks between f/2.8 and f/4. Corner sharpness (shown by the dotted red line) doesn’t reach the same level as centre sharpness, but does steadily improve from f/1.4 to f/5.6. For the best edge-to-edge sharpness it should be used around f/5.6-f/6.3. Diffraction has the affect of softening images at f/16.
The caveat of using a lens wide open is the vignetting it can introduce at the edge, but in some cases, such as for portraiture, it can be quite appealing. Our tests reveal the corners of images appear darker than the centre by approximately 1.2EV. Corner shading becomes less obvious when it’s stopped down, with edges measuring around 0.7EV darker than the centre at f/2 and becoming almost completely absent by f/4.
With all lens corrections switched off, the lens exhibits obvious pincushion-type curvature of lines towards the edge of the frame – more than we’d expect for a mid telephoto zoom that’s equivalent to 84mm on an APS-C mirrorless camera like the Sony A6500 we tested it with. If you’re shooting subjects with straight lines near the corners and want distortion-free images straight out of the camera, you’ll want to double-check the built-in lens profile is applied.