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04-28-2014, 09:22 AM   #1
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AF Fine Adjustment - Live View

Does anyone know if there is a different method for AF fine adjustment for live few vs standard view? I have an adjustment chart and in live view this particular lens appears to be excessively front focused, while in standard view it focuses perfectly. Yet when I use the fine adjustment menu, it has absolutely no effect on the live view focus. I can go +10 or -10 and it has no effect. This is on a K-3 body with a Pentax 18-250 lens. I'll check through the manual some more, but just wondering if any of you know what's up.

Thanks,
Will

04-28-2014, 09:58 AM   #2
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There is no adjustment for Liveview AF. The AF fine tuning only works on the view finder focusing system. The theory is that Live view cannot be out of adjustment as it uses the sensor itself to focus. I don't know if that is 100% true, but I have never found a lens that was not accurate using Live view.
04-28-2014, 10:29 AM   #3
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QuoteOriginally posted by jatrax Quote
There is no adjustment for Liveview AF. The AF fine tuning only works on the view finder focusing system. The theory is that Live view cannot be out of adjustment as it uses the sensor itself to focus. I don't know if that is 100% true, but I have never found a lens that was not accurate using Live view.
Well, that explains a lot. Thanks! I have been playing a bit and found some interesting results. When I use spot focus, LV is right on. When I use multiple points, even though I'm focusing on a small flat chart on the wall several feet away, LV is very out of focus. Can't even read the letters. Same with tracking, out of focus. All done with tripod, IR remote trigger.
04-28-2014, 11:01 AM   #4
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QuoteOriginally posted by jatrax Quote
I have never found a lens that was not accurate using Live view.
Two separate optical effects, field curvature and focus shift,
could cause live view CDAF to become inaccurate.

04-28-2014, 11:15 AM   #5
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QuoteOriginally posted by theWags Quote
When I use spot focus, LV is right on.
I never use anything except spot focus which might explain why I never saw any issues. Maybe I'm not thinking straight but would you not want to use center point when testing a lens? I would think multi-point would have the chance of introducing other variables. But then I use a lens-align device not a flat chart so that might be different.
04-28-2014, 01:27 PM   #6
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QuoteOriginally posted by jatrax Quote
I never use anything except spot focus which might explain why I never saw any issues.
I actually saw quite a few 3rd party lenses had AF accuracy issue on K-01, and I also saw quite a lot threads post here complaining AF issue on K-01. Tamron 28-75 is one of them gets a lot complain.

I have tested many time, and have excluded the possibilities of AF point selection and SR related problems. And usually more obvious when the lens is stop down than wide open, unless the DOV is wide enough to cover the problem.

And it is not 3rd party lenses only. My DA55/1.4 has similar but much minor BF on K-01. The lens is very very sharp even wide open, but I was surprised to see less so at F 1.8 and 2 on K-01.

interestingly, live view (contrast detection) AF on K5II is just fine. I noticed this problem on K-01 only. I even returned a K-01 for that reason but the 2nd came with same problem. I use small primes on K-01 only so not an issue for me. Apparently, the AF chip on the camera could make mistake, even using live view.
04-28-2014, 01:47 PM   #7
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QuoteOriginally posted by grahame Quote
My DA55/1.4 has similar but much minor BF on K-01. The lens is very very sharp even wide open, but I was surprised to see less so at F 1.8 and 2 on K-01.
That sounds like focus shift.
04-28-2014, 01:55 PM   #8
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QuoteOriginally posted by lytrytyr Quote
That sounds like focus shift.
That was what I thought. But strangely it happens on K-01 only. On K5II, it is just fine with both phase (with a little AF adjust) and contrast section AF. I expect same behavior on both if it was focus shift . Plus, if I manually focus them on K-01, with small F, focus is always fine. So I will say probably not focus shift. It is rather an AF calculation issue, and somehow, someone 3rd lens are not being able to talk to camera appropriately.

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