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: Image Quality
One of the main benefits of choosing a standard zoom with a constant aperture of f/2.8 ahead of an f/4 version is the way it permits the use of faster shutter speeds in low light. The image below is a good example and by shooting wide open at f/2.8 I was able to keep the sensitivity below ISO 1000 whilst maintaining a 1/60sec shutter speed in order to keep the subject sharp and the image free of handshake. This was aided further still by the effective optical stabilisation, which does an excellent job of suppressing handshake, especially at the longer end of the zoom.
Inspecting our Image Engineering tests, which are carried out at each aperture setting at three focal lengths revealed a spike in centre sharpness when the lens is stopped down from f/2.8 to f/4, with high sharpness figures being returned between f/5.6 and f/8. Corner sharpness is better at wider focal lengths than at the long end and improves gradually as it’s stopped down to f/5.6-f/8.
While the sharpest results are obtained by stopping down, shooting at f/2.8 creates some very satisfying images. As the photographs that support this review illustrate, f/2.8 is good to use when you want to emphasise a subject from a busy background and a create pleasing bokeh in out of focus areas.
Vignetting is prominent at the wide end of the zoom at f/2.8, where corners appear approximately 1.4EV darker than the centre. Corner shading is less obvious at f/4 and by stopping down to f/5.6 it vanishes almost completely. The lens is supported by Adobe so if you find yourself shooting at wide apertures and would like to remove vignetting later during post processing you can select the Enable Profile Corrections option from within Lightroom or Photoshop and it’ll automatically and effectively correct the image for you.
It’s a similar story correcting distortion. Leave the image untouched and you’ll be aware of barrel distortion at 24mm, which diminishes as you zoom in towards 35mm. Mild pincushion distortion also appears as you encroach 70mm. This level of distortion isn’t a major concern however. It’s easily fixed by applying a lens profile and this distortion is common with most standard zoom lenses covering a wide to short telephoto focal length.