Review on Sigma 17-50mm f/2.8 EX DC OS HSM FLD Lens: Large Aperture Standard Zoom for Canon DSLR - International Version (No Warranty) by Agata Zarzycka ᠌

This is my third Sigma (after 50 / 1.4 and 18-200) and this is what I understood: you want tenacious autofocus, good color reproduction, working holes starting from 2.8 . don't buy Sigma, take your own optics. Later I bought Canon 16-35, I remember this Sigma as a bad dream. People don't be cheap! Some pros: Cheaper than the Canon equivalent. Convenient case, hood included. Has some cons Not tenacious autofocus, so-so bokeh (compared to Sigma 50 / 1.4). Trunk backlash after six months. Working holes starting from 4.0, color reproduction is poor.