DotTune: AF tune technique without taking photos

Started Jan 31, 2013 | Discussions thread
Marianne Oelund
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In reply to michaeladawson, Feb 1, 2013

michaeladawson wrote:

Horshack wrote:

michaeladawson wrote:

The flaw in the method...

The technique is dependent on the left arrow and the right arrow boundary points being within the -20 to +20 range. You're probably SOL with this method if you have lenses that require AF fine tune values above say -15 or + 15.

I think you might still be good - it's just that for the purposes of the midpoint calculation one end of the range will be fixed at -20 or +20, giving you a little less wiggle room for midpoint accuracy.

Sure. Just saying that there is a limitation to the method. I have a couple of lenses that require a number round -18. I'll have to see how this method treats them.

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Mike Dawson

Offset the lens focus a bit, so the AF fine-tune values that give you the two rangefinder transition points will be closer to 0.  Then you can determine how many fine-tune values it takes to move from one transition point to the other.

For example, if you defocus the lens slightly so that the AF fine-tune 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 fine-tune value at the available transition point.  Your ideal fine-tune will be 4 values further away from 0; that is, if a fine-tune of -15 brings you to the edge of the "green dot" range, the ideal value will be -19.

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Qualities possessed by God in infinite proportion: Love, Grace, Power, Righteousness, Wisdom, . . .
Qualities possessed by humans in infinite proportion: Ignorance.
- Marianne

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