Originally Posted by Bobfrance
You have to turn a knob which deploys a dark slide over the film to prevent the film fogging when the lens is off.
Fogging? It's to prevent the film from being exposed to light, never heard the fogging thing...
Besides this annoying contraption (which gives you a warning in the viewfinder when it's deployed, at least in the Mamiya 7), these cameras are awesome. The Mamiya 6 even kind of folds up a bit. They are great cameras, and coming from your background you'll have no problem using one.