What do the abbreviations on a Tokina lens mean?
Abbreviations A to Z
AT-X = Advanced Technology Extra. You will find this on all Tokina lenses that have special types of glass.
DX = Digital eXpanded. These lenses are only suitable for digital cameras with an APS-C sensor.
FA = Focus Clutch Mechanism. This refers to a system that allows you to switch quickly between autofocus and manual focusing.
SD = Super Low Dispersion. These glass elements are used to reduce chromatic aberration. Chromatic aberration can be seen on photos as purple borders around details with a lot of contrast.