Headline - DSLRs have imprecise focusing due to their mirrors

Started Apr 5, 2014 | Discussions thread
Martin.au
Martin.au Forum Pro • Posts: 11,911
Re: Your faulty logic

Lee Jay wrote:

Martin.au wrote:

Lee Jay wrote:

peevee1 wrote:

Lee Jay wrote:

Greg A A wrote:

Lab D wrote:

Lee Jay wrote:

conceptually, the optical paths cab be different lengths leading to consistently missed focus, and single-shot focus can be open loop.

In practice, I use closed-loop AI-servo and all of my cameras and lenses are calibrated right out of the box meaning I get 99% or so in-focus shots in the most difficult conditions. My contrast-detection cameras can't come close to matching that even with much more depth-of-field and much easier conditions.
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Lee Jay

http://www.lensrentals.com/blog/2012/08/autofocus-reality-part-3b-canon-cameras

1. Phase-detection autofocus (even using still targets and center-point only) wasn’t nearly as accurate as contrast detection.

2. The contrast-detection autofocus was about as accurate as the most careful manual focusing.

There have been many tests by unbiased sources showing Contrast Detect is usually more accurate.

For those who missed it here is a test that contradicts the test results you posted.

"The contrast detect results on the 5Dmk2 and 7D show a big focus error with a reasonable amount of variability between the shots too. This just translates to out of focus shots – plain and simple" - from:http://www.reikan.co.uk/focalweb/index.php/2012/12/af-consistency-comparison-nikon-canon-phase-detect-contrast-detect/

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f8 and be there

So 2 PDAF cameras do not perform well in Live view/CDAF mode? 2 cameras designed touse PDAF and have CDAF as an afterthought. Do you see your faulty logic? The other 2 cameras designed to use PDAF actually performed well in CDAF mode (although all 4 of them are very slow and do not have the best logic).

Sorry, but your link does NOT contradict the test results. It only show that when camera makers add CDAF as an afterthought, it may not work very well. The CDAF designed cameras are still as accurate as you can get.

On large, contrasty targets. On low contrast targets where precision is required, they often fail.

Exactly like PDAF, and for the same reason.

In my experience, dedicated PDAF is at least one, if not two, orders of magnitude better on such targets.

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Lee Jay

And yet the only cameras that are rated to focus in EV -4 are Panasonics using CDAF.

I said low contrast, not low light. Also precision (where the target occupies less than 1% of the frame).

-- hide signature --

Lee Jay

Seeing as neither of us have any experience with Panasonic's cdaf, I think it's probably irrelevant. I think one should be rather careful in applying their experience with one camera to an entire class of cameras.

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