Help. I've just received a Vivitar 75-205mm Macro lens with a Canon FD fitting along with a separate X2 Matched Multiplier. I've just noticed that many Vivitar lenses for Canons have a mount that pushes in and then locks with a screw fitment, silver gripped. The new lens and both my adapters have this. Problem is that I can't get the aperture blades to close and I want to make sure it's nothing I'm doing wrong before I return the lens. I can see the blades close on a 50mm lens using an adapter but not this 75-205. Anyone have any clues that might help, perhaps I'm missing the obvious. Adapter pic attached showing silver screw tightener.