Samsung 20-50mm F3.5-5.6 ED is an Auto Focus (AF) Standard 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 30 - 75mm. With a max aperture of f3.5 at 20mm, we can not consider this lens fast on wide end and neither at tele end with its f5.6.
Samsung 20-50mm F3.5-5.6 ED is not a weather sealed lens, so you have to be extra careful against rain and dust.