DotTune: Video Tutorial for AF tuning without photographs

Started Feb 18, 2013 | Discussions thread
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Different ranges when I change ISO
In reply to Horshack, Apr 12, 2013

I watched the video and performed the DotTune procedure using a D800 with 50mm f/1.4.  The tests were done wide open on a USAF test chart, with the camera 9 ft away from the wall.  Wireless remote shutter, sturdy tripod, non-fluorescent lighting, camera parallel to the target.

With ISO at 100, I'm getting a valid range from 6 to 11.  My midpoint would be 8.5.
With ISO at 200, I'm getting a valid range from 10 to 15.  My midpoint would be 12.5.

I did multiple tests at each ISO value to make sure to get rid of any outliers.  All tests were done in the same 1 hour time window with no environmental changes.

Any idea what might be causing me to get such a difference in values just by changing the ISO?

Any insight would be appreciated.

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