Tested in the store. I wanted to change my Tamron 15-30 2.8 to this Sigma. I wore it on 1D Mark 3, on crop 1.3 with an open aperture it gives a strong vignette at 18-24, at 35 it is no longer visible. Sharpness pleased. There is a known compatibility problem with the new Canon 70d carcasses and others, but for some reason people scold Sigma, not Canon. I will take for 40d. Tamron is too big and heavy.