I have had very limited experience with the ZD but it seemed much noisier than the Aptus 22.
The big negative for me is the fact that you can only use Mamiya lenses with it. While these can be surprisingly good, the great thing about a digital back is that it opens up access to Schneider and Rodenstock digital lenses which are quite fantastic.
Oh... and I need camera movements, so it means a digital back is needed. If I was shooting people or fashion I might have gone for a ZD, but it would be a tough decision between it and a Canon 1DsII.
i unfortunatly had the zd as one of the first owners in germany- want to say i felt at the end like their stupid testperson.
this camera is the biggest crap i ever owned in my life.
especially if you want to shot people or even worse fashion- this thing is completly unusable.
so far the quality at and beyond 100 asa is great- the handling is complete bullshit.
i dont know any client,model, portraitperson or however who wants to wait fully 2 minutes till the camera buffer is cleared after only 10 shots- jpgs or raw doesnt matter, before you can really go on to shot another 10 - the same if tethered- which has is own problems.
and mamiya germany which is based in my hometown munich- and i was their personal kown customer since 13 years - completly disapointed me ( friendly spoken).
they were at this time beginning to middle of last year completly convinced about there piece- i guess they are only theoritical technics.
and even then they should realize that the bufferwriting is completly unacceptable, as well as the menue and display (waiting up ages to show up the picture- want show before buffer is clear).
but worst of it all- the quality above 100asa is completly unusable, even with noiseninja postprod.
at the end i was so frustrated about the camera and there arrogant service and neverkeeping firmwareupgrade promises that i gave it back end of year to my dealer, while loosing a quite huge amount of cash, because the leasing company did´t like to quite my contract.
at the end i was just happy to get rid of it- and all the rest of my mamiya gear (had rz,pro645,later 645afd before)
changed to hassyh3d22 in december - which is cool now and quite a different leage to work with.
this is just my experience which i would like to tell everyone who thinks about purchasing a zd- and! wants to work prof. with it in the portrait or fashion area.