Unfortunately it seems that the FCP is not "usable" on my Nikon D850 DSLRs with my old Nikkor 28-70mm, that previously worked perfectly with the WACP-C....
Looking the chart port Nauticam for the FCP, it seems that the 28-70mm is usable only from 35mm to 70mm ... so the angle of view is only of 122° and not 170° at 35mm...
With the WACP-C this angle was 130°... more or less....
I am very sad... because I have already sold my WACP-C... 🥴