Stanley,
Our experience with this lens for over decades is that is can be sharp on the edges if you shoot it stopped down enough. F12 should be fine but you can do a refraction test to see if stopping it down too much will loose sharpness. I suggest shooting one at 8 and start bracketing on 1/3 or 1/2 stops, then compare all images in Capture One or PS at 100% or 200% to see if you detect any loss of sharpness.
The complaints we have seen is that is is not as sharp as the 35mm BR, well that is true. And the edges can tend to get soft as you enlarge the image when making big enlargements from the files. It is what it is because its the only one in that category. Many would go to a tech cameras where they could use a Rodenstock or Schneider lens to get better edge sharpness. Most of these folks were making big gallery prints.
Shoot ti tat F5.6 and you see the softer edges people may be eluding to in your comments. There was also some techniques people were using to sharpen the out 30% of the image more that the entire image in order to sharpen up the edges. We all know how that sharpening works on our files, it is always best to get it sharp thru the lens.
Also the IQ140 being a cropped sensor will be more forgiving since it not using the entire lens but the sweet spot. We usually got pretty good results from the crop sensors with both the Phase One/Mamiya 28mm and also the Schneider 28mm. IQ4 150 MP back like you are using does tend to be more demanding with all lenses so keep that in mind as well.
I bought this lens, at a very low price, some time ago from a reliable member who wasn't using it and who claimed it was sharp at f12. There was some additional discussion on the thread concerning sharpness. This image was captured at f12 on a tripod and does appear quite sharp edge to edge.
If anyone has experience with this lens, I would appreciate your input.
Stanley
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