Major frustration in D800 AF Tuning even with DotTune Method

Started Jan 24, 2014 | Discussions thread
Horshack Veteran Member • Posts: 7,240
Re: Major frustration in D800 AF Tuning even with DotTune Method

Sounds like you're doing everything right. I'm not sure why you're midpoints from test-to-test at the same distance have outliers but if I average your results for each distance I get 1.58 for distance "137" (so use either +1 or +2), -.25 for distance "167" (use either -1 or 0), and -1.66 for distance "236.5" (so use -2 or -1). Even with the outliers you seem to be getting a pretty consistent average midpoint across all distances, and the average midpoint looks good.

Regarding your midpoint outliers, try this target in place of the Atkins target and see if you get more consistent results from test-to-test. I've been doing experiments with different targets and found the cross-hatch one to produce the most consistent results. Please report back on whether it helped you.

As for focus distance, it is true that the shorter distances produces the lease DOF and so intuition might say that shorter is better since it would reveal focus differences more. In practice I've found the opposite is true - even though longer distances have more DOF, long distances also many times reveal the need for AF tune much more than shorter distances do. At first blush this makes the short vs med/long distance results look like distance-specific tuning variation (and thus the impulse is to average the midpoint distances), but in actuality I've found that the tune value derived at the mid-to-longer distance works well for short distances as well whereas the opposite is not true (using the short-distance tune value for other distances doesn't work well). My conclusion then is to try tuning at mid to long distances for cases when the short distance seems to produce a significant different midpoint than other distances. As for what specific distance to use for "mid" to "long" distance...for some lenses (like the 50G f/1.8 and f/1.4), I've actually found infinity sometimes works best...and so I have to use a outdoor targets in these instances (like a far tree, house, etc...).

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