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02-05-2009, 08:20 AM   #16
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QuoteOriginally posted by jeffkrol Quote
canon's tolerances for consumer vs pro AF was "within the depth of focus" vs "within 1/3 the depth of focus" not depth of field btw.. subtle difference.
http://doug.kerr.home.att.net/pumpkin/AF_accuracy.pdf
Interesting read, but that's not really what it states.

02-05-2009, 05:09 PM   #17
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Sadly not what you want to hear, but I had my original K20 replaced by Henry's ( here in Canada ) with about 2 days to spare on their over the counter exchange policy limit.

The only time my LBA has ever served me well.

I had the same issue, real trouble with crisp sharp focus, on pretty much every lens ( some + AF adjustment some - ) most right to the max adjustment capable.

I took it back, hoping that it wasn't operator error ( and that I really was a decent photographer as my K100 suggested ! ) and three test shots with my body and the store's display model with my FA 50 1.4 and voila, new body, new warranty and an apology.

Now all is good in my K20 world............except that I have no time to use it...........or post pictures ( which makes sense, cause I'm not taking many ) or post on the only forum in all of gods internet that I really care about.

Hope this helps.

John
02-05-2009, 11:07 PM   #18
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QuoteOriginally posted by AdrianM Quote
I have been having a few problems with focus on my K20D.
I believe your camera was knocked out of calibration when it was serviced.

Nothing to do with overexposure, AFAIC.

Your focus chart shots look like they were taken under tungsten lighting which will cause some front focusing. But the amount of FF and your real world experience all lead me to the same conclusion: Your camera needs to be recalibrated. You could do some experiments to find out whether the sensor or the AF system is not in the correct position anymore but it doesn't really matter. CR Kennedy should service the camera free of charge to you and if I'm not mistaken they owe you an apology for messing it up.
02-05-2009, 11:10 PM   #19
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QuoteOriginally posted by Wheatfield Quote
My K20 is far enough out that I can't bring some of my AF lenses into calibration.
Do you intend to have it serviced?

I agree with your that QC these days isn't what it used to be with many companies. Price is a factor but also most people don't seem to bother so companies get away with it.

02-06-2009, 02:26 PM   #20
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QuoteOriginally posted by pingflood Quote
Interesting read, but that's not really what it states.
Probably not. I (mistakenly??) assumed higher precision AF modules were reserved for the "pro" models". Maybe pro and FF? Maybe not. Whatever models have the large aperature sensors.
Canon, Inc. usually states, in the published specifications for their various digital
single-lens reflex (SLR) cameras, an accuracy tolerance for the autofocus (AF)
system in terms of a fraction of the depth of focus of the camera. Often, for the
“basic” AF mode, that specification is “within the depth of focus”. For the “high
precision” AF mode that applies in certain circumstances, that specification is often
“within 1/3 the depth of focus”.
Often, users ask, “Isn’t that the same as ‘within the depth of field’ (or ‘within 1/3
the depth of field’)?” Usually the response is, “Certainly not—those are two vastly
different quantities.” But in fact the answer isn’t quite that simple.


In many of the cameras of interest, Canon’s AF accuracy specification for certain
situations (for example, for one of the center AF detectors of certain cameras when
the aperture of the lens is greater than a certain value) is “within 1/3 the depth of
focus”.
Does the happy situation we discussed


02-06-2009, 04:17 PM   #21
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Thanks for all the comments guys. I'm pretty sure that something is screwy in this particular camera. It seems to treat all lenses equally (ie badly). I dropped it off at the Pentax rep for warranty repair yesterday afternoon. I'll drop a line on the forum when I get it back. Fortunately, I still have my K10D to play with.

cheers
02-06-2009, 06:55 PM   #22
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QuoteOriginally posted by jeffkrol Quote
Probably not. I (mistakenly??) assumed higher precision AF modules were reserved for the "pro" models". Maybe pro and FF? Maybe not. Whatever models have the large aperature sensors.
Canon, Inc. usually states, in the published specifications for their various digital
single-lens reflex (SLR) cameras, an accuracy tolerance for the autofocus (AF)
system in terms of a fraction of the depth of focus of the camera. Often, for the
“basic” AF mode, that specification is “within the depth of focus”. For the “high
precision” AF mode that applies in certain circumstances, that specification is often
“within 1/3 the depth of focus”.
Often, users ask, “Isn’t that the same as ‘within the depth of field’ (or ‘within 1/3
the depth of field’)?” Usually the response is, “Certainly not—those are two vastly
different quantities.” But in fact the answer isn’t quite that simple.


In many of the cameras of interest, Canon’s AF accuracy specification for certain
situations (for example, for one of the center AF detectors of certain cameras when
the aperture of the lens is greater than a certain value) is “within 1/3 the depth of
focus”.
Does the happy situation we discussed


Most (all?) of the Canon cameras have a mix of AF sensitivities. For instance, my 1Ds2 has something like 9 cross-type (high precision) points and the rest are horizontal only. Generally the higher precision points only are high precision at a certain aperture, e.g. 2.8 or 4. The same goes for the 40D, 5D etc though in different variations... it's not that one camera gets all "pro" AF points and another all "consumer" ones
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