i only have experience with my two sigma lenses (24-70 2.8 and 70-300 f4) and my all manual 8mm peleng all used on my 20d. when i was in best buy looking around for a new TV i went over to the cameras and i played with a 40d they had with a canon 28-135 lens. the autofocus on this is incrediably fast when comapred to my sigma lenses. is it normal for canon brand lens to be much faster? i did a quick search of the site to see if anyone has asked this question before but couldnt come up with anything.