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| p.3 #14 · p.3 #14 · DotTune: New AF tune technique, no photos required |
I have set all my lenses up by eye
I found that my ability to do this by eye, despite being careful, shooting lots of test images, was not nearly as reliable as either DotTuning or FoCal.
Case in point at one time, based on what I thought were extremely rigorous manual inspection of test images,I had a +5 value set for my Sigma 35. In real life, I wasn't getting reliable focus.
Tons of testing using FoCal, and now not very much testing using DotTune, point to the right value for my lens/camera as being -7 or -8 (-7.5 if that were possible).
What I like about the DotTune method is that it uses the very algorithms that the camera uses. Thanks to our D800's having two (three, actually) different focus methods - Contrast Detect (CD or Live View), Phase Detection Autofocus (PDAF), or manual focus by eye/enlargement - we can use CD or manual focus (with live view) to establish the base-line focus.
All DotTune is doing is getting AF Tune set so that when the camera uses PDAF it agrees with the Contrast Detect or manual focus baseline, and, importantly, agrees *for that lens*.
Based on what we know today this makes so much sense I wonder why none of the makers publishes the approach in their user manuals.
As I mentioned earlier, if I use badly aligned targets and/or poor lighting and/or insufficient distance from the target, DotTune (or any tuning approach) will give different results. Do it all correctly, and the results I've found are repeatable and repeatability is usually a good sign of being on the right track.
I probably have more confidence in what DotTune is doing because I've seen the results of Reikan FoCal's "focus consistency" test for my lenses and know there is indeed something looking like a simple curve where peak focus reliability is in the middle of the curve. At the very least DotTune is going to get you very close to the right value that should be used for a particular lens/camera combo and that is worth something indeed given how much time it can take eye-balling it. Maybe you are better at eye-balling than I am!
At any rate I'm getting very reliable results now; I wasn't before. I have confidence in the D800's AF now; I didn't before.