Sigma 300mm F2.8 APO EX DG HSM is an Auto Focus (AF) Telephoto 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 300mm. With a max aperture of f2.8, this is a fast lens.
Sigma 300mm F2.8 APO EX DG HSM is not a weather sealed lens, so you have to be extra careful against rain and dust.