Looking for clarification on something. Plan to use Nikon FM for night photography, where I want to leave the shutter open for a few hours to capture star rotation. The exposure meter will not be needed. If I use the film advance lever to advance the film, and cock the shutter, once I lock down the shutter button with the cable release, is it necessary to leave the film advance lever in the stand off position, where the exposure meter is still active? I would like to be able to close the advance lever to preserve battery life. Thank you in advance to anyone knowledgeable on this subject.