The phrase you are looking for is "purple blobs" - a google search for "Mamiya ZD purploe blobs" will uncover a lot of information about this.
@ Max,
The purple blobs was not same issue but another that photographer Frank Doorhof wrote of that was limited to a faulty ZDs in a certain batch/batches of ZD back only. What you are experiencing appear to be exact same as I wrote of under title "ZD has Problem" at
www.luminous-landscape.com ;
http://www.luminous-landscape.com/forum/index.php?topic=22698.0
Above was what I pointed out nearly three years ago. What I pointed out then was that there were from what I had learnt issues relating to the then "limited" design of the ZD - both hardware and firmware side. Leaf Aptus 22 has identical sensor from Dalsa and has per what I know not had same problem, thus what I was told in late 2007 frank makes sense. Per posts here on Getdpi I thought Phase One and Mamiya had reduced that problem, however what you show in photos seem very identical to way I would have expected my old ZD camera to perform. I sold it at loss because it was simply unusable product for my landscape photography, namely when you have much light and same time shadow in photo. However it also showed this when exposing neutral to test sample filling half frame with white and remaining with near black subject under diffused natural lighting indoors.
I went with Leaf Aptus 65 and have had no similar problem.
With above experience and I recommend you following:
1. Get Capture One since it is developed by Phase One who owns major controlling share in Mamiya. If any software includes a fix to tune down the problem, it is likely Capture One. I also recommend that software because it is way better than any other raw converter I have used. Capture One also works excellent for my Leaf Aptus files with conversion profiles direct implemented with Leaf, thus if anyone have made good for ZD it must be them.
2. It might not be popular among many, but crush the black by adjusting the black point to give less shadow details. That should reduce the problem.
3. With Capture One PRO I can guess it can also work to tune down the issue by color adjusting with a narrow focus on the purple that ZD creates by using the color tool.
4. I recommend testing your ZD back and doing so also of others in the shop you bought it from have. When Mamiya agent here in Hong Kong tested in early 2008 they found frank same problem on each ZD back and ZD camera they had in stock, simply by photographing a test chart with neutral exposure and observing purple in black frame on test chart...
5. You may also wish to do a thorough search on
www.luminous-landscape.com to read up on problems of ZD and what serial numbers those had to ensure that you was correctly sold a new and not old ZD. The critical is the last letter in ZD serial number (or was it the the first?). There is different numbering of ZD back and ZD camera.
Regards
Anders