This new Tokina lens is the first in a new generation of full frame (FX) lenses designed for professional digital SLR cameras like the Canon EOS 5D Mark II and the Nikon D700 and D3x. The 16-28 zoom range gives the professional photographer a super-wide angle of view to get close to subject for dramatic effect or to take in entire scenes. NEW Silent DC Motor with GMR senor The 16-28 f/2.8 uses a newly developed silent DC motor that allows the lens to focus faster and more quietly then previous generations. The DC motor coupled with a new GMR magnetic AF sensor work together to increase AF Speed. Ashperical and Super-low Dispersion glass elements A new, 56mm in diameter, large sizes aspherical glass element is incorporated into the front lens group, while there are 2 more aspherical elements in the rear group. 3 SD super-low dispersion glass elements are also incorporated through-out the optical design to reduce chromatic aberration, give maximum resolution, more even brightness and distortion correction. One-Touch Focus Clutch Tokina’s exclusive One-touch Focus Clutch Mechanism allows the photographer to switch between AF and MF simply by snapping the focus ring forward for AF and back toward the camera to focus manually. There is no need to change the AF/MF switch on Nikon camera bodies* and there is no second AF/MF switch on the lens for Canon, everything is accomplished by the focus ring.