On Apr 4, 2012, at 14:27, George Sinos wrote:
> OK, I found my answer, and some animated examples here.
> <http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html>
>
Cooool. Thanks!
> The short story is that phase-detection measures the error and tells
> the lens which direction and how far to move to get into the correct
> position. It's faster, but depends on everything being calibrated.
> Sort of like saying "go three feet to the east and you'll be there."
> If you both have accurate rulers and compasses it will work fine.
>
> The contrast detection method used with live view is iterative and
> keeps sending correction messages until the image is focused. Slower,
> but more accurate.
>
I've noticed the differences when watching the focus dials. In Live-View
(contrast-detect) mode the camera swings wide and then bumps back and forth
over the line in smaller and smaller iterations until it stops at the focus
point.
In phase-detect ('standard') mode, you hit the AF button and it pretty much
just jumps to the final spot. There is a little very-quick fine-tuning once
it's there, but nothing like the wide swings you see when it's focusing in
live-view.
-Charles
--
Charles Robinson - [email protected]
Minneapolis, MN
http://charles.robinsontwins.org
http://www.facebook.com/charles.robinson
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