Review of the Sigma 10-20mm f/4-5.6 EX DC HSM

Sigma makes this lens for a variety of mounts, including its own SLR range, but only the Nikon, Canon and Sigma mount versions have the HSM, or Hyper Sonic Motor function. Pentax and Sony versions don’t, while there is no version available in the Four-Thirds format. Otherwise the lens is constructed from fourteen elements in ten groups. Of those elements, one is a glass-moulded aspherical lens, and two are hybrid asphericals. The optical train also features three SLD (Super Low Dispersion) lenses. Build and handling Like the Nikon 12-24mm lens, this is a heavyz unit at 470g, with high construction values. The traditional Sigma EX finish doesn’t suit everyone’s taste, though I like its matt hammerite-like look. The rubber zoom and focus rings certainly feel secure, but there’s slightly more resistance in the zooming action than others. The focus ring is slightly stiff too, though has a comforting dampened feel to it, making it feel very smooth. The version we tested has the HSM motor, which is quiet and quick, but has a slightly more juddery feel than similar Nikon or Canon lenses. Image Quality Sigma usually makes very respectable wideangle lenses – and have been pioneers in wideangle zooms. However, the results from the 10-20mm lens are slightly disappointing. Corner sharpness is a particular bugbear; the Sigma lens simply displayed more instances of corner smudging than any of the other lenses on view. Central sharpness is good, but not outstanding, while fringing is apparent at times throughout the examples we shot. The lab tests show very good resolution but prone to fringing, by quite a high degree. At 20mm this is better controlled. Distortion is very well controlled throughout the range.