[Don Hoey]

This mount carries over the Aperture Indexing ring from older pro series cameras and does not make use of the EE servo post, so there is no switch on the lens mount perifery.
The AI tab is a solid part of the ring so once again unmodified pre AI lenses cannot be used.

With D type lenses the aperture needs to be set to minimum for metering to work. Aperture is changed by the mode dial. Inclusion of the aperture ring on these lenses is for backwards compatability. They even have an AIS groove that is not used on any of the modern cameras.

The aperture indexing ring comes into its own when using AI/AIS lenses and auto bellows.
With AI/AIS lenses the camera can be used in manual or aperture priority mode with metering. As these lenses do not contain a chip to provide communication of the selected aperture, the AI ring serves that purpose and enables aperture display in the viewfinder.

Don