Sigma 50-200mm F4-5.6 DC OS HSM is an Auto Focus (AF) Telephoto 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 75 - 300mm. With a max aperture of f4 at 50mm, we can not consider this lens fast on wide end and neither at tele end with its f5.6.
This lens features on optical image stabilization which helps capturing sharper images at lower shutter speeds. Sigma 50-200mm F4-5.6 DC OS HSM is not a weather sealed lens, so you have to be extra careful against rain and dust.