AI lens
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Manual Nikkor lenses, produced from 1977 until mid 80s, introduced Automatic Maximum Aperture Indexing, designed to let the camera body know what is the maximum aperture of the mounted lens for metering. Non-AI lenses coupled to the camera's meter through a system that required a pin on the camera to be mated to a slotted prong on the lens before the lens was mounted, then the aperture ring on the lens had to be turned from one extreme to the other to index the meter to the maximum aperture of the lens. AI eliminates this entire procedure because meter coupling and indexing occur automatically when the lens is mounted on the camera. Most AI lenses made until a few years ago were also supplied with the coupling prong so they would be compatible with either metering system. With all-black barrel, rubber focusing ring and multicoated elements.
