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This is the photo of the lens mount of an F-mount Tokina 10-17 mm (taken from online). What is the lever that I marked in red for? Note that this is not the aperture lever (which you can also see on the bottom right).
The extra lever is the "Maximum Aperture Indexing Lever" or "Lens Speed Indexing Lever". It was added on some AI-S lenses to transmit the maximum aperture information to the camera body.
It was only used on FA & F4 camera bodies for more accurate automatic multi-pattern metering.
Required, but never shown