After a comment that the image I posted had purple blobs, I decided to text my ZD back with a printed 16x20 target made up of graduated monochrome steps. Using a ZD back on an RZ IID, 110mm lens, 1/400 f32 with strobe lighting, iso 50, I shot the target.
This is the same setup that I used for several pieces of artwork. I discovered two things. Any purple blob issue was obscure. But, I had dead pixels showing as dark spots larger than one pixel. I called Mamiya on Thursday. They requested that I send them the back for replacement. The replacement arrived today.
Just shot the test target again which is attached. Sorry, it is a jpg and not very exciting but revealing. Close up you will see blemishes. THEY ARE IN THE PRINT.
I am very pleased with the response from Mamiya. I am also in love with the back on my RZ (and AFD). The RZ setup in the studio is great.
I did not test the ZD at higher ISOs. I was shooting at f32 as it was.
I started shooting weddings with an RB67. When I wanted no noise, I used pan-X pushed to ASA 100. When speed, Tri-x and lived with the noise as part of the process.
Thank you, Mamiya!