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 - 600mm. With the max apertures of only f4.5 at 100mm, and f5.6 at 400mm, the lens is quite slow at both ends.
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.