There have been some comments in forums that the ZD back had update over the ZD camera. Thus I asked Mamiya's Hong Kong agent on the subject. Following are the replies from them on my two emails:
It should be no image quality difference between ZD camera and ZD Back because their specification is the same, for example their image sensor is
using DALSA's 48mmx36mm Full Frame RGB Square-structured CCD.
The difference between them is the attached Mamiya PhotoStudio CD of ZD Back is the latest version (v1.30) instead of the ZD camera's CD v1.10 or v1.20 (v1.20 improved noise reduction parameters and it can update form www.mamiya-op.com.jp
web site, the latest package will be v1.30) but it should be very little image quality difference between them especially if you are using Photoshop to retouching or processing Mamiya raw image files, it should be no difference.
I'm afraid that the only image quality difference between them is ZD Back can be use on RZ67proIID camera and the image is RZ6x7 lens quality instead of 645 lens quality.
Basically they are really the same spec. I shoot the picture from both of them is the same quality.
The advantage of ZD is compact and the operation just like a 135 camera. ZD Back is more convenience to be use on difference camera body( Mamiya 645AFDII, RZ67proIID). The out-looking seem pretty like professional camera than ZD.
You can visit our web site to read the spec. of them. For the Mamiya software Remote Capture function(Capture image directly transfer data to the computer instead of CF or SD storage). ZD camera is better than ZD back because you can adjust all the setting in the computer (e.g white-balance , shutter speed etc.) before you shoot the picture.
ZD back only shutter release and auto-focusing function, the other setting remained in the camera body.
Actually, we are deeply appreciated that you are interested in Mamiya digital product.