There goes Rufus again, falling off the wagon.
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From the mid sixties most SLR cameras have had full aperture TTL metering.
That is the iris stops down to shooting aperture at exposure, it remains open before exposure to keep the viewfinder bright for focusing. Meter coupling, and these days electronic interfaces, tell the meter how much to compensate the reading for.
So if you have an f2.8 or faster lens, the af is performed at f2.8 or faster, even if you shoot at f8 all the time.