With higher resolution HD images, achieving focus takes longer and is more difficult than ever. Since focusing errors are also more noticeable, precise focus is of paramount importance.
Understanding this fact, Canon developed its new Instant AF system. Instant AF offers accurate auto focusing at ultra-fast speeds.
Instant AF employs a unique combination of two AF techniques: TV AF and External AF. TV AF systems, although very accurate, are slow to respond when a subject changes or moves. Incorporating additional high-speed External AF sensors into the lens allows Instant AF to rapidly spot changes in the subject, identifying its position and distance accurately and at speed. This frees the TV AF sensor to perform the necessary super fine focusing adjustments vital to the best quality images at HD resolution.
Put in simple terms: Instant AF makes capturing super-sharp HD video easier than ever before.