AF tunning what actually happens?????

Started 11 months ago | Discussions thread
Robin Casady
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Re: AF tunning what actually happens?????
In reply to Roy Kikuta, 11 months ago

Roy Kikuta wrote:

Roy Kikuta wrote:

I've used about a half dozen nikon DSLR models thus far, but have never seen the AF system (using PDAF) do more than a single focus operation to achieve (what it thinks) is in-focus status. Looking thru the VF as I press the AF-ON button, I would expect to see something akin to "hunting for focus" operation if the AF system really performs a close-loop feedback operation to do iterative phase detect comparisons and issue multiple drive commands as necessary to achieve perfect focus - and I've never seen this. All the bodies I've used so far perform one continuous focus operation, lights up the green focus confirmation dot in the VF, then stops - unless you're in AFC mode and the the subject is moving - on static subjects, never. I guess I'll keep on looking for more info. Thanks for the discussion. Aloha!

I guess you've never used a Micro-Nikkor 105mm f/2.8 VR lens.  I've certainly seen AF hunt for focus.

It looks like I have to eat my words re. how many iterative phase comparison/drives are performed in a PDAF operation according to this article by Roger Cicala of LensRental: http://www.lensrentals.com/blog/2010/07/how-autofocus-often-worksAccording to Roger, the PDAF system is so fast it CAN perform multiple cycles of phase comparison/drive commands in order to achieve perfect focus. Faster than I could see when looking thru the VF, anyway I'll have to take time to read the article a couple of times to digest it fully. Cheers!

In my limited experience writing code of an Arduino running a stepper motor, I would expect a simple check phase-move-check phase loop to run fast enough to seem like one smooth movement.

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Robin Casady
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"Get your facts first, then you can distort them as you please."
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