SIGMA 24-70MM F2.8 DG OS HSM | ART

A bigger, weightier proposition than Sigma’s previous 24-70mm, the new ‘Art’ lens promises a boost in build quality and all-round performance

Some 25 per cent heavier than its predecessor, Sigma’s new Art lens weighs in at just over a kilogram. It feels much more solid and substantial in the hand, the outer barrel combining a metal shell with TSC (Thermally Stable Composite) material. As you would expect in a premium lens, the mounting plate is also metal, and features a weather-seal ring, although the other joints and switches around the lens are not weather sealed.

Placement of the two control rings is the same as in the Tamron lens, with a fairly narrow focus ring at the rear and a larger zoom ring towards the front. Both lenses feature a focus distance scale beneath a viewing window. Canon photographers will feel at home with the zoom ring, which increases the focal length when twisting anti-clockwise (viewed from the rear). This is opposite to Nikon zoom lenses, and the competing Tamron.

The zoom and focus rings both operate very smoothly and precisely, the former having markings for 24, 28, 35, 50 and 70mm. The Tamron omits the 28mm marking. In both lenses, the inner barrel extends by about 30mm as you extend from minimum to maximum zoom setting. The Sigma doesn’t have a zoom lock switch but didn’t suffer from any zoom creep in our tests. Focusing is fully internal, so the front element and filter attachment thread doesn’t rotate.

Autofocus is fast and quiet, based on a revamped HSM (Hyper Sonic Motor) system that delivers a third more torque than in Sigma’s previous lens. Even so, the Tamron’s autofocus proved marginally quicker and slightly quieter in our tests. As usual with ring-type ultrasonic systems, full-time manual override is available in Single/One Shot AF mode, once autofocus has been achieved. However, the Sigma has an additional MO (Manual Override) autofocus mode, available from a three-position AF/MO/MF switch on the barrel. This enables manual override before autofocus has locked onto a subject in Single AF mode, as well as in Continuous/AI Servo mode. It’s a feature that’s lacking in the Tamron lens.

As with the Tamron, there’s a straightforward on/off switch for optical stabilisation, without a dedicated panning mode. Throughout the zoom range, we experienced an effectiveness equivalent to four stops, which is an improvement over some of Sigma’s older lenses.

We’ve found the previous Sigma 24-70mm to be lacking in outright sharpness, especially at its widest aperture of f2.8. The new

Art lens fares much better in this respect, delivering very good centre sharpness when shooting wide open, throughout the zoom range. There’s also less falloff in sharpness towards the edges and corners of the frame. Meanwhile, bokeh is pleasingly smooth when shooting wide open, and remains good when stopping down a little, thanks in part to a wellrounded nine-blade diaphragm.

Helped by the inclusion of three SLD (Special Low Dispersion) elements, colour fringing is quite well controlled and, again, it’s an area of performance in which the Art lens beats its predecessor. Distortions are also fairly minimal for a standard zoom, with well-restrained barrel at 24mm, negligible distortion around 35mm and only a little pincushion between 50mm and 70mm.