And just one more possibility for the focal reducer slash phase detection module. Either of these could be built into lenses independent of each other. One way to put really fast AF into mirrorless cameras might be to build a phase AF sensor into the lens itself. You could use a small transluscent mirror embedded in the optical path of the lens, and so long as it's capable of communicating the correct information with the camera, bingo, phase detection lenses! These could augment the camera's AF in certain scenarios or take over entirely depending on use.
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