Olympus ED 50-200mm f2.8-3.5 SWD is an Auto Focus (AF) Telephoto Zoom lens with FourThirds max sensor coverage. When mounted on a FourThirds sensor camera, it will give you an FF equivalent focal range of 100 - 400mm. With a max aperture of f2.8, this lens is fast on wide end. The long end is also quite fast at f3.5.
Olympus ED 50-200mm f2.8-3.5 SWD is weather sealed which makes it an ideal lens for outdoor use, especially when coupled with a weather sealed camera body.