Another brilliant aspect of Canon’s Dual Pixel CMOS AF technology is that its developers realized from Day One that to work effectively, it would have to provide the AF that video users need. Not just simply “getting things in focus,” but getting it done the way a pro video camera operator would want to.
When we shoot still images, we normally want the fastest focus response possible. We press the button on the camera, and we want and expect that the image will jump into focus, without hunting back and forth, and without indecision from the AF system.
But video is different. If the sharp focus during a live video recording just instantly jumps from one distance to another, it’s normally a very jarring visual experience for viewers. Think about it: this is rarely done, unless for a very special, sudden visual impact, in movies or most TV shows. Instead, professional-recorded video normally smoothly transitions, or “racks,” from one distance to another. There’s usually a smooth and much slower progression as focus changes from a foreground to background, or vice-versa.
Canon’s Dual Pixel CMOS AF does the same thing, when Movie Servo AF (sometimes labeled “Servo AF”) is active. Focus is deliberately slowed down, so that changes have a professional, smooth look to them.
And, on advanced EOS models (like the EOS 80D and 5D Mark IV), you have additional menu controls: