Fujifilm XF 100-400mm F4.5-5.6 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 150 - 150mm. With the max aperture of only f4.5 at 100mm, it is considered a slow lens.
This lens features on optical image stabilization which helps capturing sharper images at lower shutter speeds. Fujifilm XF 100-400mm F4.5-5.6 is weather sealed which makes it an ideal lens for outdoor use, especially when coupled with a weather sealed camera body.