I bought this lens to use with my 30D and 40D bodies. On these 1.6x crop bodies, it's equivalent to a standard 28-55mm lens, a very useful wide-angle range for landscape and scenic photography. After reading several reviews and researching other lenses, I selected the Tamron. It's a third the price of the Canon 17-40L, and produces comparable image quality. There's slight softness in the corners wide open, as is common with lenses in this focal range, but stopped down to f/4 or smaller, it's sharp and clear, with good contrast and no noticeable vignetting. Focus is quick and accurate. Not as sturdy as some lenses out there, but for the price, build quality is very good.