At any rate, with the om-1 you can lift the mirror, but the diaphragm closes when the shutter goes off. The point I tried to make is that in Reese's tests there is a different outcome for the same lens (!) and different bodies. An om-1 was used and an om-2000, which has diaphragm prefire (in the 100mm 2.0 test; me bad).
Cheers, Jan