Originally posted by Jens Lyn IV Nowhere in this process does the film or image sensor play any role in focusing. IBIS does not, and indeed cannot, affect the AF sensor in any way. The AF sensor does not move.
The AF sensor does not move, this is an empirical fact. But the Sensor does, quite a bit actually. The IBIS system needs to spool up whether you are using it to stabilize a shot or not, this process introduces lag, which is compounded by AF lag*. And all this has to happen before the mirror has even flipped up and the first curtain gets moving.
* which depends on the lens, its fastest aperture, focal length, type of AF drive, subject magnification etc etc so on, and so forth.