The Tokina AT-X PRO 17-35mm F4 FX is a wide-angle full-format zoom lens. Its optical scheme consists of 13 elements in 12 groups, including three aspherical elements and two Super-Low Dispersion glass elements with the properties close to fluorite (FK01 and FK03 on the scheme).
It features a new built-in Silent Drive-Module. Combined in one module, a motor and a gear reducer feature low noise characteristics. The autofocus of the Tokina AT-X 17-35 mm f/ 4 PRO FX functions faster and more accurately thanks to a new high resolution focus detector..
The Tokina AT-X 17-35 mm f/ 4 PRO FX is equipped with the so called One-touch Focus Clutch Mechanism, i. e. the choice between manual focusing and auto-focusing modes is realized with one touch. In order to switch autofocus mode you should slightly shift the focus ring forward. To engage manual focusing the focus ring should be shifted back to the camera.
Evaluation of Tokina designations:
AT-X (advanced technology extra) - the lens is designed by means of advanced and new technologies and high-quality materials.
PRO - models with this designation have an aluminum coating to improve its reliability and have an ergonomic look corresponding with its high quality.
AF for autofocus.
FX - for film and digital SRL Canon EOS and Nikon F cameras.
IF - internal focusing (the lens does not extend, the front element do not rotate).
SD - Super Low Dispersion glass is used to minimize aberrations and increase contrast.