Sigma 15mm F2.8 EX DG Fisheye is an Auto Focus (AF) Wideangle Fisheye Prime lens with 35mm FF max sensor coverage. When mounted on a 35mm FF sensor camera, it will give you an FF equivalent focal range of 15mm. With a max aperture of f2.8, this is a fast lens.
Sigma 15mm F2.8 EX DG Fisheye is not a weather sealed lens, so you have to be extra careful against rain and dust.