Pentax 12-24mm F4.0 ED AL 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.
Pentax 12-24mm F4.0 ED AL is not a weather sealed lens, so you have to be extra careful against rain and dust.