AF Fine Tuning - Dot Tune method, Trials, Tribulations and Focus Tune

Started Nov 4, 2015 | Discussions thread
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Bill Dewey Veteran Member • Posts: 7,910
AF Fine Tuning - Dot Tune method, Trials, Tribulations and Focus Tune

Yesterday I decided to try the Dot Tune method of AF Fine Tuning. I have been using Focus Tune for several years with good results, but have heard that Dot Tune yields results as good or better and is faster and easier to do, so I decided to give it a whirl. I use a Nikon D810 and D7200, and wanted to tune my 400 f2.8 AFS-1, 300 F4 PF and 70-200 F4. To make this even more fun, TC-14E, TC-17E, TC-20E. 3 lenses, 3 TC's and 2 bodies, 12 combinations for each body.

I had started on Saturday with Focus Tune for lenses I could do in my house, basically 400mm and less due to distance. Finished yesterday outdoors at 50-70 feet for the longer lengths. For both methods I was using the Focus Tune target.

Watch the video more than once for Dot Tune. Not hard, but you do want to get the steps correct. Be sure to start at zero, I think, my results were more consistent that way. I also found that lighting on the target does matter. As the day got later my target was in shadow and my results sucked. Brought out a light from the garage, lit the target, much better.

The worst problem I had was keeping my *$(%* finger off the back button. Muscle memory wants to use that thumb, not the half-press the shutter. Tape your thumb to your hand, this will save you time.

Pay attention to the video where it speaks to getting a "feel" for the "flicker". Once I got this, things went quicker.

One change I made is that moving by 1 step at a time seems silly, so I would jump by 5 or 10 to find limits more quickly, then move by 1 or 2.

My findings were interesting. Between the two methods there were several times where the settings were identical, and where they were not identical they were 1 or 2 points off. To me this validates both. Dot Tune is faster, if for no other reason than you don't have to copy a bunch of files to the computer and run the software. Given how close the results were, speed wins. The nice thing about Focus Tune is that it gives you a nice graph, I'm just not sure what it all means, but it sure seems empirical.

As a last test I took test shots using the Focus Tune ruler to validate all the settings. I did adjust a few my a couple of points, not sure this was really needed but it seemed like a reasonable validation. One thing this did show me is the AF variability. At times I could see a shot to shot difference on the ruler.

I do have a couple of questions about the process, and will send a PM to the "inventor" inviting comment.

1. The Target - I saw on the video that a new target is recommended. As noted above I used the Focus Tune target, how large should the target be printed?

2. Is the distance to target affected at all by the size of the target?

3. As noted above I did notice differences when the light was less, is it better, even in daylight, to add a "fill" to remove shadows?

As a general note, I have been VERY skeptical of the whole notion of this Dot Tune method, almost to the point of commenting that it can't be "as good" as other methods. Consider this my public apology, thanks to the inventor for educating me a bit as well as for providing something that just plain works.

I will cross post this to the "other" site to be sure of the broadest possible coverage. If you have any specific questions you would like to ask, feel free to ask here or send me a PM.

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Bill Dewey

Nikon D7200 Nikon D810
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