Samyang 12mm f2.0 is a Manual Focus (MF) Wideangle Prime 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 18mm. Providing a max aperture of f2 at 12mm, this lens is very fast.
Samyang 12mm f2.0 is not a weather sealed lens, so you have to be extra careful against rain and dust.