Thank you for you answer Paul.I do have a DF, but I don't really enjoy the body. I like the mamiya RZ with the waist level finder, but it's way too heavy and I want autofocus and metering, so I thought it might be possible to use the XF.
As indicated above, the XF only accepts IQ1/Credo and more recent. The P65+ was a stellar back, and still compares very favorably to the best that small format can offer (a tribute to Phase One quality, given the back is 12 years old). But if you want a more modern body you'll need to upgrade it. Contact your local Phase One dealer for pricing to upgrade the P65+ to a more recent back, and to demo the XF which is lightyears beyond the legacy DF platform. If you're in the USA we'd be glad to be that dealer for you; Phase One is our passion.