Question about D4 and D800 auto focus capability while shooting video

Started Feb 20, 2012 | Discussions thread
AgentHEX Contributing Member • Posts: 676
Re: Question about D4 and D800 auto focus capability while shooting video

MrSkelter wrote:

AF in photography has to lock once and then the shot is taken.

Video requires continuous focus. That means when DOF is low a decision has to be made either to move the focus point, or allow slight drift.

Again, so does AF in general.

when the drift becomes too great in an important region of the frame the focus is adjusted.

Camera's do not have the processing power to make that subtle a focus decision.

So how does regular af do it?

They simply track. This causes problems when slight movements should be ignored, and can lead to mistakes when the wrong part of the image is being tracked.

I.e. If a man kicks a ball towards the camera you may want to keep his face in focus and the camera may track the ball.

Again, how is this any different from the problem with ANY AF? Remember no AF can focus on two planes at the same time.

With a still shot you can choose your focal point in advance. With video your focal point has to move over time meaning changing the focal point during a shot is greatly complicated.

AF in video can work. It's just very, very difficult at the moment. If you're shooting quality video you focus manually.

So, basically, AF is hard, except it's been done quite well on just about any SLR. Hey, they even know which direction to focus and how far off they are.

F*cking cameras, how do they work?

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