I have borrowed a 150mm sonnar lens and a 2x multiplier and I am having problems. The lens shutter speed and fstop rings will not turn, they are locked on 4 and B and the lens will not shoot. Also there are three metal levers, one is marked with V X M next to it, what are these for. The multiplier is in great shape but I was wondering what are the adjustments for exposure, how many stops do I adjust for. I hope you guys can help, thanks............James