Any lens will fire with a digital back when set to the manual 1/400 orange dot. But if you want other shutter speeds, that won't fly. OK for studio lighting but not balancing or mixed lighting.
I gave up on trying to use a Leaf back on an RZProIID. It worked, it wouldn't work. Leaf America confirmed a firmware bug with the exact combination of ProIID, Mamiya adpater, Leaf Aptus 22 in full electronic mode and also had issues with the plate, Leaf cord from back to lens, all a clusterfuck.
In the end, I sold my Aptus, wasn't shooting it much anymore. Selling off Mamiya gear and keeping a basic ProII film kit. RZ's are great cameras. Great when shooting film and getting the real 6x7 frame.
I am not familiar with the Leaf on RZ, but with Phase, it is very nice. other than my own fumbles, or lack of practice before actual use, I think the RZ is great!
And to clarify, it is the bezel plastic on mine that cracked and broke, yet the buttons are still in tacked and working.
I need to make a note in my RZ case for the RB limit. I have the winder, the tilt, the tubes, the L bracket.... I actually used a canon flash that worked Ok with it mounted/bounced. I need to use it more :-)
As far as Canon, I usually keep it on M, indoors, and Tv or Ap, but often I use P, as I use 35 mainly for street/journalistic shoots...more off the cuff, spur of the moment instances.
Yes, custom functions and combo of the buttons to hold and change take some time. I have been with the 1Ds for a long time, and a bit more natural with it.
but now that I have a workstation setup in my living room, when i come home, I grab RZ and shoot the family and have fun looking over the images instantly!
