Can you imagine trying to photograph a horse with a manual focus lens? How about a racehorse? How about an entire horse race? How about the finish line at the Kentucky Derby?
That's exactly the situation that sports photographers used to find themselves in. Back in the days when the best sports cameras had no autofocus whatsoever – let alone subject tracking and animal detect and algorithmic AI processors – and fired about 6fps on a good day, getting any shot in focus required true skill.
