Here's the problem with your camera, I have the D40 that has the same problem! You need to buy the lenses that have built in autofocus motors built in whereas the the higher up cameras such as the D90 don't need this feature in the lenses, hence the price difference of lenses! ie you can get the older cheaper lenses to work on the likes of the D90! pleas note you can use the cheaper lenses on the D40 and D5000 but you can only focus manually! But still a waaay better camera than the fuji(no offence to anyone here who owns one) and sigma hsm lenses are a good value for money lense!