see also:

• Micro Four Thirds system
• http://eng.faq.panasonic.com/app/answers/detail/a_id/26478/~/what-is-dfd-(depth-from-defocus)-technology%3F---dmc-gh4

Image courtesy of imaging resource's explanation of DFD

• mirrorless cameras with only CDAF sensors have trouble with AF on faster moving subjects and also continuous AF subject tracking
• Panasonic's solution introduced with the Panasonic GH4 4K video stills camera is their Depth from Defocus DFD AF technology which unfortunately only works on the latest Panasonic cameras and ONLY when used with DFD-compatible Panasonic lenses
• this uses the CDAF sensor data to determine how much the incremental change in focus changed the contrast and then used this data to more rapidly set the lens focus closer to the in-focus region, thereby minimizing focus hunting, but to determine this, the camera needs to understand the bokeh characteristics of that lens at each focal length (if it is a zoom lens)
• thus the DFD capable camera has a database of the bokeh of each older Panasonic lens, while newer lenses will have this data stored within the lens thereby avoiding need for camera firmware updates whenever a new lens is released
• the alternative solution other manufacturer's have turned to is on-sensor PDAF

• it appears all Panasonic Micro Four Thirds lenses are - and perhaps Four Thirds?
• Olympus lenses are NOT compatible with DFD - the Panasonic camera will resort to normal CDAF
  • Panasonic could add Olympus lens bokeh data to their camera firmware but perhaps for marketing reasons are not interested in doing so