Shocking insight: AF is not a closed feedback loop!

Started Jul 18, 2003 | Discussions thread
OP Mishkin™ Contributing Member • Posts: 917
Is that the reason WHY AF is not implemented as a loop?

You're right, direct link between measured lens position and a signal from AF sensor allows for lens focusing on moving subject. I guess, the loop system can do this, too, but it will require extremely fast convergence of the loop and running the loop many times per second, which is probably beyond capabilities of AF systems. This is also mentioned in that Honeywell patent.

Other than that, I don't see WHY AF is not implemented as a closed feedback loop.

hyslopc wrote:

Unless I've misunderstood, you couldn't make the AF a closed
feedback loop and still support moving targets. Since many targets
move, the AF would constantly be re-adjusting itself and would
never "lock" - sound familiar? That's right, I've just described
Canon's AI-Servo mode, which constantly and continuously
re-focusses for as long as you half-press.

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