If there is no level then the camera can't control the aperture on G lenses. There is a level. It's inside the flange (not outside like the aperture feeler tab which the FTZ doesn't have). This level exist in all F mount Nikon and originally it's called the stop down level. Originally it will stop the lens down to the set aperture on the aperture ring during the actual exposure. Later on when Nikon introduced the FA this level became the aperture control level that is leaving the aperture ring in the minimum position would allow the camera to use this level to stop the lens down to any aperture. When Nikon introduced the G lens with no aperture ring this level is the only mean to control the aperture. With the new E type lenses with electronic diaphragm there is no need for this level but the FTZ has to have it to operate the G type lenses which are the majority of the Nikon F mount lenses out there.