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Author Topic: AF accuracy - some good articles by Roger Ciala  (Read 959 times)

ErikKaffehr

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AF accuracy - some good articles by Roger Ciala
« on: August 03, 2015, 01:28:10 am »

Hi,

Roger Ciala of LensRentals published some interesting observations a while ago:
"Conclusions
This really wasn’t a “conclusion” post; our intention was to just demonstrate some autofocus basics that most people know already.

Live View (contrast-detection) AF on a still target is more accurate than phase-detection AF. It should be so. Contrast detection is using the actual sensor to determine focus; phase detection is not. Overall we found about one shot in ten was out of focus with phase detection.

Live View AF is as accurate as Roger View MF. You may be better than this, or you may not.

Phase-detection AF has more shot-to-shot variation than contrast detection. It’s not huge, but it’s real. This shouldn’t surprise anyone. Phase detection was developed for fast AF speed and to detect subject movement. It wasn’t developed to be more accurate.

Microfocus adjustment pulls good phase-detection AF results up to a par with Live View, but it doesn’t eliminate the small amount of shot-to-shot variation that phase-detection AF has." From this article: http://www.imaging-resource.com/news/2012/07/23/autofocus-reality-part-1-center-point-single-shot-accuracy

The image below shows latest generation AF technology from Canon:


While the image here shows and older generation of AF technology:


All from this article:
http://www.lensrentals.com/blog/2012/07/autofocus-reality-part-ii-1-vs-2-and-old-vs-new

Best regards
Erik Kaffehr
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Erik Kaffehr
 

AFairley

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Re: AF accuracy - some good articles by Roger Ciala
« Reply #1 on: August 03, 2015, 10:50:56 am »

It would be interesting to see if PD autofocus has improved in the 3 years since the article was written.  Anyone who has used Michael Tapes' LensAlign focus tuner software has seen the shot to shot variation that occurs with AF.  However, though his software shows the variation, I have no idea of how to tell if the amount shown is significant.
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