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The way of controlling the aperture by the camera body is easy! The aperture of the lens is stopped down to the preset value. The image on the left shows the Nikon F while exposing. If you press the shutter release button the aperture lever travels completely down, the mirror flapps up and the shutter opens. With a small screwdriver I simulate the camera's aperture lever - the aperture is fully open. The aperture ring of the f/2.8 lens on the right is set to F8. If you look through the viewfinder of your Nikon camera, the aperture of your lens is kept open by the aperture lever of the camera body (see arrow). It even would have been reliably possible for AI-S lenses, but that is another discussion. I guess Nikon rated this trick as unprofessional for themselves - the professional F4, introduced in 1988, offers no S or P mode with non-CPU lenses. It was a trick, which made us to believe that AI lenses could work in shutter priority mode. AI oder AI modified lenses don't allow that.

The truth is: only AI-S lenses allow the control of the aperture. In the "Nikon News", a magazine of Nikon Germany and Nikon Switzerland, they tried to explain us the advantages of the AI-S lenses in conjunction with the FA, but they only beat around the bush.

On the other hand Nikon's marketing department told us, AI-S lenses would be the perfect match for the FA. Even here everything works with AI lenses, too. Not a bit of it! The P mode of the FG works with every AI-S, AI or AI modified lens! More than that: in 1983 the semipro FA was introduced, the first Nikon with shutter priority mode (not counting the DS-attachments for the F2). We all expected that the P mode only works with AI-S lenses. In 1981 the replacements were completed and Nikon announced the FG, the first Nikon SLR with P mode, for which the camera body must control the aperture. In that time some German photo magazines reported about changes in the F-Mount and assumed that the "new" lenses allow the camera body to control the aperture. In the following months they replaced all their AI lenses with AI-S counterparts without talking it up. In 1979 Nikon began to build the first AI-S lenses: the series E lenses. But you should read this one: Using older lenses on your Nikon DSLR Thus, if you like to use older lenses on your modern camera, this article is not of interest for you.

To begin with, every Nikon DSLR or Nikon SLR introduced after 1988 does not distinguish between AI and AI-S lenses.

The difference between an AI lens and an AI-S lens