Sigma 10-20mm f/3.5 EX DC HSM £330, $450
High-end features come at a bargain price
The autofocus system is quick and quiet, and image quality is boosted by the inclusion of one SLD (Special Low Dispersion) and two ELD (Extraordinary Low Dispersion) elements. These help to maintain good sharpness and contrast, while keeping colour fringing low. Undercutting the Tamron 10-24mm for price, the Sigma doesn’t stretch as far in terms of zoom range, but has pretty much the same maximum viewing angle. Build quality feels better in the Sigma, and higher-end features include a ring-type ultrasonic autofocus system. This improves handling, as the focus ring doesn’t rotate during autofocusing, while also adding the bonus of full-time manual override.
Another feature that’s unique among the DX-format lenses on test is the constant-aperture design. The Nikon and Tamron 10-24mm lenses match the Sigma’s f/3.5 rating at the short end of the zoom range, but it is two-thirds of an f-stop faster at the long end, as the other two lenses shrink to f/4.5.