I've just bought a DP-3 finder on the 'bay as an upgrade over my DP-1. On the front right bottom corner (when viewed from the nameplate side) there is a chrome tab sticking down with a small cylindrical tip. What is that for? For clarity, I'm not referring to the pin that indexes with the prong on the lens. I've checked the MIR site and didn't see any reference to this tab -- the best I can figure from the photos there is that this tab might have something to do with the DS-2 EE aperture control.