Sigma's 18-35mm F1.8 DC HSM has generated a lot of excitement since its announcement in April, as the fastest zoom ever made for SLRs. Designed for use on APS-C / DX format cameras, it offers a 28-54mm equivalent zoom range, and promises similar depth of field control to an F2.8 zoom on full frame. But can an F1.8 zoom really work? Read our detailed review to find out.