Tamron 17-50mm f/2.8

The Tamron SP 17-50mm f/2.8 Di II LD Aspherical [IF] Lens made for the DX-format Nikon F-mount DSLRs incorporates a motor built into the lens itself, which gives it the capability to autofocus with all Nikon DSLR cameras (including the D40 and D40x). In addition, with the motor built into the lens, focusing will be quieter and more responsive.