I have a D40 and just learned that it does not have an internal motor. I am still not clear about the F vs G vs D mounts, but I do know that you must have a lens that is AF-S or AF-I to Auto focus. I did not know this when I bought my 50mm f/1.8 (it's still a very good lens for my style... but trying to manually focus on a constantly moving one year old is proving quite difficult!)