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Archive 2012 · Testing AF and problem assessment

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p.1 #1 · p.1 #1 · Testing AF and problem assessment

I returned my 1st D800 due to left AF problem. I just got the 2nd replacement D800 and have been doing AF testing using byThom testing process.
Here are the results:
24 F1.4 lens, 1.4, ISO 100, shutter speed 100- Left, Center, Right are all blurry compared to Live View. The acceptable sharpness of test images were with AF Fine Tune setting at -10 to -15. The test results were inconsistent, if AFT was at -10, the L focus was sharp, but the right AF was not quite sharp.
50 F1.8 lens, 1.8, ISO 400, shutter speed 100- Left, Center, Right are all blurry. The best images/acceptable sharpness was with AF Fine Tune setting at -5 to -10.
I am a bit confused on how to interpret the results. Do I have left or overall AF problem?

Aug 08, 2012 at 11:33 PM
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p.1 #2 · p.1 #2 · Testing AF and problem assessment

Tune the center AF point first, and be sure to get it as precise as possible. Then using that tuned value, take the following sequence of photos for the Center, Extreme Left, and Extreme Right AF points (repeat for each):

* 2 Live View Photos
* 10 Phase Detect (Viewfinder) photos, rack focus between each photo

Load images into your computer. For each set of photos (per AF point), pick the best of the two Live View photos, then compare that to each of the 10 phase detect photos. There is shot-to-shot variability of phase detect AF, so some "misses" can be expected within your set of 10, ignore those. Use the best 5 photos against your Live View photo to evaluate the focus. If you have the Left AF issue, it's likely your center will be the sharpest relative to its Live View photo, followed closely by your Right AF point, with your Left AF point being noticeably blurry. Keep in mind that at wide apertures lenses are softer at the edges than the center, so don't compare the sharpness across AF points; only compare the relative sharpness of the each AF point's Live View photo to its Phase Detect photos. Here's an example of good focus:

Aug 08, 2012 at 11:43 PM

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