One Touch Focus Clutch: Tokina’s 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.
Tokina Optical Technology: Aspherical Optics – a standard lens is made up of a combination of spherical lens elements. Individual “lenses” within the lens are commonly referred to as “elements”. A spherical element has an even curve to the surface of the glass. However, there can be problems with such elements; light entering the centre of the lens and light entering at the edge may not be perfectly focused at the same point. This is called spherical aberration. More enhanced computer assisted optical designs are creating lenses with more spherical elements. More spherical elements within a lens means a higher risk of spherical aberration having a negative impact on optical quality.