I dont want to start up a debate. I am just wondering on the differences between the mounts and focusing. Most (except less common lenses such as tilt shift) Canon lenses are either EF or EF-S right? Canon EF fits, if im not mistaken, all current production body mounts. So, i dont know much about "focusing motors" is there one in the body and one in the lens? or what? I have the XTi, I can auto focus any current canon ef lens right? When it comes to nikon isnt there a few bodies, lets say D40, that cant auto focus on some lenses? I dont use Nikon so im a little confused.... Do all Canon DSLRs have auto focusing?