Sigma 500mm F4.5 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 500mm. With the max aperture of only f4.5 at 500mm, it is considered a slow lens.
Sigma 500mm F4.5 EX DG HSM is not a weather sealed lens, so you have to be extra careful against rain and dust.