The AT-X 280 AF PRO is constructed with high quality optical glass multicoated lens elements created by Hoya Corporation, the world?s largest manufacturer of optical glass. Two Aspherical lens elements and one SD (super low dispersion) glass element are employed in the optical design to insure critical sharpness across the film plane. One aspherical element is molded as one piece of optical glass created with technology pioneered by Hoya. The other is a hybrid aspherical element.
Focusing- An internal focusing mechanism with a Tokina Focus Clutch Mechanism gives this lens fast auto focus. The focus clutch feature, a signature of the Tokina PRO series lenses, allows the manual focus ring to be snapped forward to an auto focus position. This disengages the ring from the focus gearing and provides a faster, smoother auto focus operation. When snapped back to the manual focus position, the ring is damped for a smooth manual focus action not normally found in today?s auto focus lenses.
A refinement of the focus clutch mechanism has been incorporated in the AT-X 280 AF PRO Nikon and Canon mount, so that now the lens? focus ring can be snapped back to the manual focus position at any time. It is not necessary to change the AF/MF switch (on the body with Nikon or the lens with Canon) every time the lens is changed from auto focus to manual focus mode.
Internal focus means the 77mm filter threads do not move during focusing. The advantage is when a special effects filter is used it is not necessary to readjust the position of the filter every time the focus is changed.
The AT-X 280 AF PRO is what is commonly referred to as a parfocal lens. This means that if focus is achieved at 80mm, then the lens is zoomed back to 28mm, the subject will still be in focus.