Difference between a non USM and USM lens??
Hello. I'm looking to buy myself a DSLR camera (probably a Canon EOS 400D Digital Rebel XTi). It comes with the 18-55mm lens kit and you can get a EF90-300mm non USM lens fairly cheaply with it. I was wondering, what is the difference between a non USM lens and a USM one? I've noticed most people have USM lenses but im not sure what it means. :-[ Help appriciated. :)
