The tamron sp af17 50mm f28 xr di ii ld aspherical if lens made for the nikon slr system 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 the tamron sp af17 50mm f28 xr di ii ld aspherical if is a lightweight compact fast standard zoom lens designed exclusively for digital slr cameras the fo