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p.24 #18 · DotTune: Autofocus Fine Tuning in under 5 minutes  
schlotz wrote:
snapsy,
I've reread Marlanne's workaround and it still confuses me (maybe I'm just slow). Her example of defocusing slightly followed by coming up with a value of 4 is clear enough BUT the next step starting with "Then put the lens back at perfect focus" does not make sense. Putting it back to where you started just sets the AF range back to over +/20 so how would it now come up with 15? Just does not make sense to me.
Could you explain? I've added the text from her workaround below so others might benefit.
Thanks,
Matt
Marlanne's Workaround:
Offset the lens focus a bit, so the AF finetune values that give you the two rangefinder transition points will be closer to 0. Then you can determine how many finetune values it takes to move from one transition point to the other.
For example, if you defocus the lens slightly so that the AF finetune values at the limits of the "green dot" are at +2 and 6, then you know the difference is 8. Half of that difference, or 4 away from either transition point will be the correct adjustment.
Then put the lens back at perfect focus. Find the finetune value at the available transition point. Your ideal finetune will be 4 values further away from 0; that is, if a finetune of 15 brings you to the edge of the "green dot" range, the ideal value will be 19....Show more →
The full procedure with her workaround is this:
* Perform a DotTune to find the confirmed range. Let's say it's +15 through +20 (ie, still confirmed at +20)
* Slightly defocus the lens so that the confirmed range shifts to within the +/ 20 AF tuning scale
* Perform a 2nd DotTune with the defocused lens to find the full width of the confirmed range.
* Apply the 2nd DotTune range to the 1st DotTune range to establish the full range, take the midpoint
Example:
* 1st DotTune produces +15 through +20 (still confirmed at +20, so 6+ point range)
* 2nd DotTune with defocused lens produces +5 through +12 (8 point range)
* The effective DotTune range is +15 through +22 (+15 starting point, with 8 point range from 2nd DotTune applied). Midpoint is 18.5 (use 18 or 19)
