Tokina 12-24mm f4 DX is an Auto Focus (AF) Wideangle Zoom lens with APS-C / DX max sensor coverage. When mounted on a APS-C / DX sensor camera, it will give you an FF equivalent focal range of 18 - 36mm. With a max aperture of f4 at 12mm, we can not consider this lens fast on wide end but f4 at 24mm is not too bad for tele end.
Tokina 12-24mm f4 DX is not a weather sealed lens, so you have to be extra careful against rain and dust. Tokina 12-24mm f4 DX was replaced with Tokina AT-X Pro 12-24mm f4 DX II Canon EF. Follow the link to read our comparison of these cameras: Compare Tokina AT-X Pro 12-24mm f4 IF DX Canon EF vs Tokina AT-X Pro 12-24mm f4 DX II Canon EF