>>3455219That's just because it's not a very challenging scene to focus. You either focus on Chelsea's eyes (which will be moving with your thrusts, but predictably, so you just get into the rhythm and take the shot at the same point where you focused) or you go focus on the cock (which will be moving perpendicular to the focal plane since you can't shoot from inside her uterus, so works with plain old single-shot autofocus without any complicated technique. Except, again, you want to take the shot when the guy's dick is on an out-stroke or it just looks like their pelvises are pressed against each other and you can't really tell they're fucking per se).
Source: I've photographed people fucking before.
