I wouldn't say hardly any at all, the majority of lenses are AF-S and can be used with the D40, any Nikkor lens can be used, its just those without the autofocus motor in the lens will have to be manually focused, which may or may not be a problem for you. However, this is the minority of lenses, but does unfortunately contain the superb 50mm 1.8 prime. The image quality of the D40x is also better than the D50 you'll find.