At the budget end of the market, Sigma and Tamron are the major scrappers and Sigma's 10-20mm lens is the cheaper of the two.
Despite its low cost compared with lenses from Nikon and Canon, the Sigma feels robust and has silent HSM autofocus. Designed for SLRs with APS-C-sized sensors, rather than full frame, the 10-20mm is available to fit Canon, Nikon, Sony/Minolta, Pentax and Sigma.
While handling is good, image quality doesn't match it. Sharpness is disappointing in the centre and even more so towards the edges. On the plus side, there's practically no vignetting, even with a filter fitted, while ghosting, flare and purple fringing are kept under control.
Colour rendition and contrast are good. All in all, it's only the lack of outright sharpness that lets the Sigma down.