The new Tokina AT-X 116 PRO DX is an ultra-wide angle lens with a fast f/2.8 aperture for better photography in low-light situations. Many photojournalists consider having an f/2.8 aperture a must for any lens in their camera bag. Based on the award-winning optical design of the AT-X 124 PRO DX (12-24mm f/4) lens, the new AT-X 116 PRO DX has a slightly shorter zoom range to maintain optical quality at wide apertures. 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 cameras** and there is no second AF/MF switch on the lens for Canon, everything is accomplished by the focus ring. Will not AF when used on Nikon D40 SLR camera body