The Tokina atx-i 11-16mm F2.8 CF is designed as an ultra wide angle zoom lens for APS-C sensor DLSR cameras. It is the only f/2.8 fast ultra wide angle zoom lens for APS-C sized DSLR cameras in the current market (according to internal survey September, 2019).
The useful 11-16mm focal length is chosen in order to position this lens as an easy demanded gear after standard zoom lenses or initial wide angle zoom lens to start with.
A constant maximum aperture of f/2.8 throughout the entire zoom range is realized to achieve great results in low light environments, for depth of field control and easy manual shooting, while maintaining a reasonable size and weight of the lens.