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07-06-2010, 07:14 PM   #1
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Contrast Detect breaking down?

Normally, contrast detect seems very accurate, due to the nature of the algorithm and its horrendous speed. However, while doing focus testing with my Tamron 70-200mm and wanting to see what exact focus would look like and how sharp it would be, I decided to use contrast detect.

I don't have access to my photos I took with it, but it was this same setup on a tripod with 12s timer as this one:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/105666-normal-...ml#post1098728

However, from what I remember, it was at somewhere between 10mm and 20mm front focused. This is with repeated tries, resetting the focus, etc. I didn't try different apertures or focal lengths at that time.

This was center point focus with nothing else even close to the center as seen from that picture.

When does CD break down and why?

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