Nikon lenses perform flawlessly shooting directly towards light. They are sharp, but with less micro contrast than the Leica R lens, for example. Highlights have a beautiful slight glow.
In 1977 Nikon introduced a new system for coupling the lens to the camera’s exposure system. This new coupling system was called Automatic maximum aperture indexing or AI for short.
The AI-S lens was created in 1982 when the aperture mechanism of the AI lens was enhanced to feature automatic aperture control.
The big difference between AI and AI-S is that the relationship between how much the camera moves the little lever that closes the aperture and how far the aperture closes is now standardized.