Canon EF 400mm f/4 DO IS II USM EF400mm f/4 DO IS II USM Instructions - Page 12

6. Power Focus (PF) Mode Using the playback ring enables smooth focus change. This is a useful feature for changing focus when shooting movies.*1 With the focus preset switch set to OFF, set the focus mode switch to PF. Rotate the playback ring to change the focus. When the playback ring is rotated in a certain direction, focus changes in the same direction as when the focusing ring is rotated. You can make a 2-step change in focus shift speed depending on the angle that the playback ring is rotated to. *1 Power focus (PF) will work while a Live View image is displayed on the camera or when shooting movies for the following cameras: EOS-1D X, EOS 5D Mark III, EOS 6D, EOS 70D, EOS REBEL T5i/700D, SL1/100D, T4i/650D, T5/1200D EOS M2*2 and EOS M when used together with Mount Adapter EF-EOS M *2 Not available in certain countries and regions. ENG-11