Autofocus has changed so much in the last decade that older ways of judging lens performance can feel oddly outdated. It used to be enough for a lens to acquire focus reasonably fast and land accurately most of the time. Today the demands are far higher. Modern cameras track eyes in motion, detect animals and vehicles, and fire long bursts while constantly recalculating focus between frames. In video, they perform smooth continuous transitions while the microphone sits only inches away, ready to expose every mechanical click and scrape.