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Author Topic: How does Mk. III handle 2 micro AF adjustments?  (Read 9099 times)

TrumpetPower!

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Re: How does Mk. III handle 2 micro AF adjustments?
« Reply #15 on: May 01, 2012, 06:57:12 PM »
One question remains unanswered, though: how do you pick the right value for adjustment!?  :-\

There's only one reasonable answer: Reikan FoCal. It (automatically) makes multiple exposures at multiple AFMA settings and does a statistical analysis to determine the setting most likely to result in the highest percentage of in-focus shots.

As you've noticed, the system's margin of error is bigger than the smallest AFMA adjustment. Thus, if you take a single shot at 0, click the step adjustment in tethered live view three times to get it in focus, and conclude the "right" value is therefore +3...well, it could very easily be that the single shot was a fluke and you'll instead get better results with a setting of -1.

Unless you perform the type of statistical analysis that FoCal does, you'll never actually know for sure.

Cheers,

b&

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Re: How does Mk. III handle 2 micro AF adjustments?
« Reply #15 on: May 01, 2012, 06:57:12 PM »

neuroanatomist

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Re: How does Mk. III handle 2 micro AF adjustments?
« Reply #16 on: May 01, 2012, 08:04:03 PM »
One question remains unanswered, though: how do you pick the right value for adjustment!?  :-\

There's only one reasonable answer: Reikan FoCal. It (automatically) makes multiple exposures at multiple AFMA settings and does a statistical analysis to determine the setting most likely to result in the highest percentage of in-focus shots.

Yes...for the subject distance you tested at, and for a zoom lens, the focal length you tested.  I can do the same thing FoCal does, manually with the LensAlign - it just takes longer. The fact that my manual values closely match those from FoCal confirms that.  But if you change the subject distance and/or focal length, the determined value usually changes.  Unless you always shoot at a particular distance and, for a zoom lens, a specific focal length (or two, if you have a 5DIII or 1D X), selecting the AMFA (or two of them) to assign to a lens (one that's applicable to the range of distances and focal lengths) requires an informed compromise. There's more to it than 'f/ocal and forget it'.
EOS 1D X, EOS M6, lots of lenses
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TrumpetPower!

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Re: How does Mk. III handle 2 micro AF adjustments?
« Reply #17 on: May 02, 2012, 01:59:32 AM »
Quote
There's more to it than 'f/ocal and forget it'.

Well, of course the system isn't perfect. And, again of course, you should put some thought into how you use your tools. If you always shoot one particular way, optimize your system for that; otherwise, the 20x focal length is a good all-around compromise. And you need to know and understand the limits and how to work with and around them.

FoCal is the best tool I'm aware of for determining the optimum AFMA setting, but it's up to the photographer to determine the optimum environment in which to use that tool.

b&

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Re: How does Mk. III handle 2 micro AF adjustments?
« Reply #17 on: May 02, 2012, 01:59:32 AM »