Aiming to improve on the default design, the Leofoto CF-01 is a replacement for the original foot supplied with the Canon EF 200-400mm f/4L IS USM Extender 1.4x , EF 300mm f/2.8L IS II USM, EF 400mmf/4 DO IS II USM, and EF 500mm f/4L IS II USM lenses. The CF-01 replaces Canon's original lens collar foot and provides a lower profile and a lower center of gravity for a better balance.