OK I have a crop camera and I know it is 1.6x factor on EF. therefore a ef 50mm = 80mm. now here is where I do not understand: on a EF-S lens is the crop factor still 1.6x the lens value so a ef-s 65mm is really 117mm. I just trying to understand what the benefit of crop camera lenses are if the lens has the same focal length as a EF lens. my understanding the EF-S 10-22mm is the same focal lens as a EF 16-24L lens, why produce a lens EF-S, when on a crop camera you could just add a EF 16-24mm L lens (other than cost).