I just recieved a new sigma 24-70 f2.8 zoom for my canon 20D. It was to replace my older version which is a sigma 28-70 f2.8 but when I did some simple brick wall tests I found, to my great surprise, the older lens is substantially sharper at almost all apeture settings and focal lengths. The upper left corner of the 24-70 is especially out of focus making me wonder if the lens is a bad copy. Anyway back it goes to B&H and I will get in its place a canon 50mm f1.4, the lens I really wanted in the first place. I will do the same experiment when the Canon 50 comes (Sigma 28-70 vs. Canon 50) and post the results. All best. MD
