This is really baffling, and have tried unmounting and remounting the lens at all different apertures. The window reads f/5.6, and I cannot get the aperture ring, when mounted, to mode from f/5.6, despite being a f/2.8. It looks like the rabbit earts engage with the pin, but then I cannot cycle through the other apertures to get it to index. It just sticks at f/5.6. My 50 1/4 Ai, 50 1/8 Ai, and 35 3.5 AiS, all couple and aperture perfectly.

Is there anything I have to do on the Photomic head, or on the lens, to get this combination to couple, meter, and work?