Designed for full-frame cameras, the Tokina AT-X 17-35mm F/4 give photographers a new wide-angle option. With a focal length of 17mm at the wide side the lens yields a spectacular 103.9 degree field of view which is great for shooting in tight situations or for taking in wide expanses of space. A bright, constant f/4.0 maximum aperture, makes it ideal for low light photography. Two Super-Low Dispersion glass elements and one aspheric glass element produce superior contrast and sharpness, and help control chromatic aberration. Tokina's One-Touch Focus Clutch Mechanism provides a quick and simple way to switch back and forth between autofocus and manual focus. The lens has been designed using improved seals, making it "water-resistant" (not waterproof), so that damp conditions won't spoil your shooting expeditions.