Well I had a Nikon F modified so that I have the option of it having 2 steps when taking an exposure.
A Rangefinered F? My friend, Pete Smith, turned my shutter button into a two step process. First step takes the shot, then the second punch on the shutter button slaps the mirror. This allows me to, 1. Make my shot almost totally silent and 2. there is virtually no vibration, allowing me to shot at 1/15 or even 1/8 of a second without shake. After that I just press the shutter button again to allow me to advance the shot. Voila it really works very nicely. Of course I can always just shot the old fashion way by pressing the shutter button a little harder for the full deal. Cool?