Leica 16-35mm F3.5-4.5 ASPH is an Auto Focus (AF) Wideangle Zoom 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 16 - 35mm. With a max aperture of f3.5 at 16mm, we can not consider this lens fast on wide end and neither at tele end with its f4.5.
Leica 16-35mm F3.5-4.5 ASPH is not a weather sealed lens, so you have to be extra careful against rain and dust.