PhaseOne P 65+ User Manual page 61

Mirror Up
Mirror up operation is only recommended if using Mamiya's own double
cable release.
The adaptor plate connects to the Mamiya body, and the switch
underneath is set to the L position (locked).
If you are using the Mamiya RZ Pro II adaptor you should set the Shutter
latency to "Zero latency"
It is possible to use Normal latency on this camera, but only when shooting
tethered from the Capture One application using the capture button.
P+ back for Hasselblad V mounted on the Mamiya RZ67 PRO II with a
Phase One adaptor.
For further information on the mirror-up on Mamiya RZ please consult
the relevant camera users guide.
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