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where you will find lots of excellent info on this and other topics. Basically, F mount up to late 70's where you had to twist the aperture ring to set indexing and the rabbit ears had no holes in them. AI (automatic indexing) followed up to early 80's, mount was modified to set aperture index, rabbit ears with holes, minimum aperture number on ADR scale is white. Followed by AIS allowing program mode with certain cameras, holes in rabbit ears, minimum aperture number on ADR scale is orange, groove milled in mounting plate. D lenses transmit distance information to camera. G lenses have no aperture ring (Nikon's new wave of forced incompatibility). Cheers. Greg.