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| p.7 #20 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes |
Why should I not use AI Servo mode while checking the "Dot"? I am in MF so I can't see any difference between AI Servo and One Shot Mode. Shouldn't I use the mode that I most use with that lens?
You actually might be able to use AI Servo since the mode may not affect the dynamics of the VF confirmation. I just happened to use One-Shot for all my testing and so didn't want to introduce an unknown variable into the procedure.
I took my initial readings under good light but when the lighting started to lessen I repeated the measurements
just for fun. Interestingly, I got basically the same "median" setting but the outside points were much less of a range. That stands to reason (I think) given that, since it has less light and therefore less contrast, the body can't read the focus as well and gives less confirmation dots on either side of the one that truly is the best focus. Does it make any sense to test under "less than optimum" light? Or is the above all false logic?
The light levels, temperatures, and subject contrast definitely affect the width of the confirmed range. In my testing the range width increases as target quality/light decreases.
Lastly it would seem that, if Dot-Tune is truly showing what it purports to, it proves that, at least in MF confirmation, these cameras are pretty darn inaccurate. Does that explain why I have had less than stellar results when using MF and depending on the confirm Dot to assure proper focus? Of course Dot-Tune does nothing to improve MF accuracy since the range of confirm Dots remains the same!
The width of the confirmation range is actually not an issue for DotTune since it only cares about the midpoint, which correlates to the maximum phase correlation and thus best focus. I actually think Canon/Nikon might intentionally be making the range wider than it needs to be to aid in faster manual focusing - if the range were too tight then some photographers might have trouble in dynamic shooting situations. For your MF lenses I suggest DotTunning them, and then whenever you shoot just try to pick the center of the VF confirmation range when focusing.