I have a Mamiya Sekor 45mm f/2.8 manual lens and when I use that on the Phase One XF camera body, a correct exposure reads -5 on the exposure meter. In other words if I use a new AF lens and set the exposure to zero on the meter for a "correct" exposure and I then mount the manual lens and set the identical exposure, the meter shows -5... I've just gotten used to this. In any case, I don't think your problem is unique
Thank you for your reply, E.J.
I also don't really think, that my problem is unique, but it's definitely different then you have) Besides the thing that in normal condition - to get a right exposure, I need to set exposure compensation to -1.7, this value is "jumping" occasionally from -1.7 to +1.0 and this is what I'm trying to resolve.
Also I'm not 100% sure that this spontaneous exposure change is depend of an aperture value, as I wrote before. It seems like, but I need to experiment a little more with it - to be sure.
However, I really hope, that this issue might be resolved by changing some custom settings in the DF camera body. My firmware version is 1.59, so the latest one, btw.
p.s: I also have Sekor 45mm 2.8, what I'm using on DF with P25 back. Love it a lot)