I am attempting to remove the shutter speed dial assembly from an Alpa 9d. I have removed the advance lever. There is a circular piece which clamps the speed indicator disc in place, am I correct in assuming that I need to remove this? I have removed the two retaining screws. Does the circular piece simply unscrew -and if so is it a left hand thread? Does the central shaft stay in place? Any help/advice would be appreciated.