Nikon has just announced a new 300 mm lens featuring a new technology called "PF" or "Phase Fresnel." This has been compared to Canon's existing DO (Diffractive Optics) lenses such as the 400 mm f4 DO. Both technologies are intended to allow creating shorter and lighter lenses, but how are the PF and DO technologies/optical elements different and similar? Is there any clear advantage to one or the other?
PF and DO terminologies are nominally interchangeable; Canon holds patents for Diffractive Optics lenses: http://www.cameraegg.org/new-canon-do-patents-500mm-f4-500mm-f5-6-600mm-f4-800mm-f5-6/
.. while Nikon has "Phase Fresnel" patents: http://nikonrumors.com/2015/01/06/nikons-phase-fresnel-pf-lens-explained.aspx/
I believe that their technologies are dissimilar essentially to the extent that they could be separately patented, and that any advantages are more likely in implementation details (e.g mounting tolerances, glass and glue chemistry) than theory.