I have been testing the sigma 50 1.4 on a 5d2 recently. I found that if the subject is over 8 feet away, the chances of mis focusing using non-center focusing point is very high (>60%). If I take the same shot using center focusing point then the chances of misfocusing drops to < 10%. This is totally unscientific and just based on my experience using it to shoot a few events. However this behaviour is quite consistent and I am wondering if I got a lemon? Just to note, focusing less than 8 feet away is almost always spot on using any focusing points.