Sigma 10-20mm f/3.5 EX DC HSM

We put one of Sigma’s ultra-wide angle lenses through its paces.

Sigma’s newest 10-20mm lens is bigger and heavier than the other Sigma model, also tested here. It features a larger front elements that requires an 82mm filter thread, whereas most lenses in the group only need 77mm filters.

Both Sigma lenses use the company’s HyperSonic Motor (HSM) autofocus, which is practically as quiet as the equivalent Canon and Nikon systems, although it proved rather slower in our tests. Full-time manual focus override is available in all the lens’s mount options, which include Canon, Nikon, Pentax, Sigma and Sony.

The biggest bonus of the new Sigma 10-20mm lens is that it has a constant maximum aperture of f/3.5 throughout the zoom range. This is very slightly faster at 10mm and just over a stop faster at 20mm. For our money, however, this alone doesn’t warrant the additional £210 cost over Sigma’s other model, as overall image quality didn’t prove noticeably better.

There’s quite a feast of glassware inside the new Sigma 10-20mm lebs, including one Special Low Dispersion (SLD), two Extraordinary Low Dispersions (ELD) and four aspherical elements. There are also Super Multi-Layer lens coatings to reduce ghosting and flare but, overall the Sigma lacked sharpness when shooting wide open, making its reasonably fast constant aperture less of an attraction in practical terms.