A premium fast ultratelephoto lens for the Nikon autofocus system, the AF-S ED-IF II 500mm f/4 is an incredibly robust lens with marked improvements from its predecessor. Using Silent Wave Motor technology to drive autofocus operation, focus can be changed from infinity to the shortest distance in less than half a second. Even more incredible, however, is the performance of the new-generation AF-S lenses when tracking subjects with erratic motion. Slick as silk, directional changes are accomplished with the ease of a jungle cat. It is this trait which will impress those who've never used the AF-S motors; while AF-D is quite competent for hunting images of fast subjects quickly approaching the lens, in unpredictable conditions they are totally outclassed by AF-S. A great lens for a sports or wildlife photographer.