>>4418455>AI: auto apertureI believe *all* F-mount lenses are "auto aperture", meaning they support being wide open during focusing and automatically stopping down when snapping the photo.
AI is "Auto indexing", it simplified the lens mounting procedure by changing how the meter knows what aperture the lens is set to. Non-AI lenses use the "rabbit ears", AI use a cut on the back of the lens. Most AI-compatible cameras physically cannot mount non-AI lenses.
>AI-S: idk the difference with AFOnly Ken Rockwell fucking knows.
Another thing about AF and AF-D is if the camera supports "highlight priority metering", it only works with AF-D or better, not AF, AI-S, AI, etc. Or at least the D750 is like that..