Does this standard zoom succeed at offering top-level performance for today’s era of high-resolution cameras? Michael Topham finds out
Sigma 24-70mm f/2.8 DG OS HSM Art review: Resolution, shading and curvilinear distortion
For our Image Engineering Tests, the Sigma 24-70mm f2/8 DG OS HSM Art was paired up with the Canon EOS 5DS R. Users of the lens will find that centre and corner sharpness improves considerably by stopping it down from its maximum aperture. Centre sharpness at all focal lengths peaks between f/4-f/5.6, with the best edge-to-edge sharpness being located between f/5.6-f/8. Corner sharpness never reaches the same level as centre sharpness and our results tell us that it delivers sharper results into the corners at wider focal lengths than it does at the far end of the zoom. Sharpness drops off beyond f/11 as diffraction becomes more prevalent.
Use the lens at the widest point in the zoom range at f/2.8 and you’ll notice that the corners of images appear darker than the centre by approximately 1.4EV. This reduces to 1EV at f/4, with shading becoming less noticeable in real-world images by the time you reach f/5.6. Vignetting isn’t quite as severe in the middle to far end of the zoom, but can still be traced in images captured at f/2.8 so it’s recommended to enable lens profile corrections if you have access to them.
Zoom lenses are prone to distortion and this lens is no different. Barrel distortion is exhibited at the widest point of the focal range, which subsides as you extend the zoom towards 50mm but then starts to turn to pincushion distortion as you get closer to 70mm. Turning lens profile corrections on and off again a few times is a good way of revealing the level of distortion you’re dealing with and how well it’s corrected for.