Way back in 1987, Canon ditched its FD lens mount for the all-electronic EF bayonet fixing. At the same time, it introduced the first usable autofocus for SLR cameras, with a fast and quiet motor inside the lens itself, and patented it as the USM (Ultrasonic Motor).
Fast forward 21 years, and we find Nikon doing the same thing. Up until now, many Nikon autofocus lenses have been driven by a motor in the body (though "AF-S" lenses have had motors inside for some time). This leaves the D40, D40x and D60 incapable of focussing many older lenses. Tamron is the latest third party lens maker to add motors for these cameras with its new SP AF28-75mm F/2.8 XR Di LD Aspherical (IF) MACRO.
As ever with lenses, the entire specification is contained within the name, a linguistic tesseract if you will. The important parts here are the maximum aperture of ƒ2.8, which stays constant throughout the zoom range and the minimum focus distance of 33cm (13"), which does the same. Although this lens will work with the cheaper Nikon bodies, the old-school 28-75 mm range suggests it is intended for use with Nikon's pro level full frame DSLRs. Price as yet unannounced.
Tamron 28-75mm f/2.8 gains motor for Nikons [DP REview]
