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03-27-2009, 03:22 AM   #1
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k20d requires -20 af to be 'close'

My k20d anti shake started playing up a while ago, actually adding shake to every image fail and ruining pictures, so it went in under warranty and they replaced its guts as far as i'm aware...(Im looking for the report back with the camera atm)

I've used this test chart:

PENTAX DSLRs: PART-2. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35

and tested the k20d under ambient sunlight, the target is printed on very high quality paper and is razer sharp and contrasty.

And I find my FA 50 1.4 prime at f2.0 is best at 'all lenses' set to -10 and the 'current lens' set to -10. (which i can only assume 'stacks' since you can put both on at the same time.)

I have a sigma 24-70mm f2.8 as well and this is best at -10- 10 also. ( feel it still is slightly front focused even then.)
So here are the FA 50 test images, (ill upload the sigma in a moment.)








So what do you guys thing? back to the shop?

03-27-2009, 04:29 AM   #2
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Okay here are the sigma results.

I get the impression both lens's should not be this badly off and they are both in need of more than the available adjustment so im well within my rights to take this back to the shop?




03-27-2009, 05:49 AM   #3
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Chart

Hi Werticus,
That does sound like a heck of a lot of adjustment. I used the same chart to calibrate all my lenses to my K20D, too, but none of them were off by more than +/- 3 or 4, EXCEPT my Tamron 70-200/2.8 which was off something crazy like -10. My own FA 50 only required -3.

That being said, it's hard to tell by your crops, but it looks like maybe you're not at the right angle to your chart. Perhaps that is the reason you're needing the overall camera adjustment PLUS individual lens adjustment? Of course I could be completely wrong, like I said, it's hard to tell by the crops. So if my perception is wrong I apologize, but the chart is supposed to be viewed at an angle, and the beauty of this particular chart (by Yvan Bourque), is that you don't need to fiddle around measuring distances and angles; just raise or lower your tripod until the big oval looks like a circle. In your cropped photos it still looks to me like a big oval.

So hopefully it's something simple like that; I know I'd sure hate to be waiting around without a camera while it was out for repair, with Spring now upon us! Good luck.
Paul
03-27-2009, 06:27 AM   #4
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a valid point neversatisfied, but I did follow the instructions exactly, even with respect to the focusing on the white and bring it down gradually to ensure its focused just on the edge of the border... and its at 45 degrees spot on and does look more or less exactly circular...

but yes i didn't trust the charts result (since it was such a bad result), but when i took the result out to the real world they seem to give better results so it looks like the chart is working.

03-27-2009, 02:03 PM   #5
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What is -10 -10 adjustment? The adjustment values only go to 10, and the "Apply to All" value does not get added to the "Apply to One" value.
03-27-2009, 02:13 PM   #6
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My question is simply this: Are you using multipoint AF or spot AF? I noticed that my sigma 24-135mm was badly back focusing when I had multipoint AF enabled, I had to adjust it -6. When I set to spot AF, my sigma was spot on at 0 again. I think the multiple AF points are messing with the AF and not choosing the point that you are necessarily wanting to focus on. That's a maybe of course just from my own observations.
03-27-2009, 02:33 PM   #7
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QuoteOriginally posted by krypticide Quote
What is -10 -10 adjustment? The adjustment values only go to 10, and the "Apply to All" value does not get added to the "Apply to One" value.
Correct. If there is an apply to one value entered it overrides the "apply to all" value. -10 - +10 is all you get.
03-27-2009, 04:00 PM   #8
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To get more reliable results I suggest using a set up with printed text taped to three CD covers as shown below:




03-27-2009, 06:11 PM   #9
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Actually, almost all your FA50 shots looks *really* soft. You didn't forget to turn off SR when putting the camera on the tripod, did you? Actually, you should have used the 2-second timer to get MLU. Check out the one with no adjustment on the fencepost.
03-27-2009, 08:30 PM   #10
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I used 2 second timer on the camera when the shots were on a tripod, which automatically disables shake reduction. SR would be on for the shots of the fence and wire and the flower seed thing. But the shutter speed was decently high.

I also never take my camera off centre point focus.

when I say -10 -10 i had both settings to -10 as i was not sure it added the two values together or not and i could see the one -10 value was not really enough.


I think my results show that my camera is out by more than -10 total and really needs a service adjustment. (the chances of two new lenses being out that much is remote). Would you guys agree?
03-28-2009, 11:32 AM   #11
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It's kind of hard to say given how soft some of those images are, but really, the ones with -10 adjustment look like the target is within the zone, if a bit further toward the back than one would expect. I'd personally leave it at that unless the thought of being without the camera a few weeks and having it possibly come back not much better seems more attractive than having a focus target that is maybe off by a millimeter or two but still within the zone. I guess I'd have to do a bunch more tests (*controlled* real world tests, like the CD one Stratario posted, not the ones where you are presenting a complex target to the AF sensor) to see if I could live with it or not.

But frankly, if that's the best the FA50 can do, I'd sent *it* back, as that looks significantly softer than what others post from it wide open. Not a focus problem, but an overall sharpness issue.
03-29-2009, 03:28 PM   #12
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Yep I had/have a problem with my Sigma 70-200 f2.8. At -10 adjustment it still front focusses. This only shows when doing close up work at wide aperture (eg. less than 3m away). I sent it and the camera in for service but it came back pretty much the same. Sigh.

FWIW my other lenses are similarly affected, but not to the same degree (from memory, -3 on the FA50 and -7 on the Tamron 17-50).

As others mention, the "Apply All" setting acts as a default for all lenses. Once you tweak a particular lens using the "Apply One" setting then that setting will override the default.
03-29-2009, 06:14 PM   #13
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yeah its only for close up focus that you can even notice a problem, at -10 it seems mostly acceptable. Im just not happy that it needs its maximum adjustment to be with in range. Normal every day shots turn out great ....
03-30-2009, 07:57 AM   #14
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Got a K20 body from B&H on Friday to have as a second body. Sent it back today. When it found something it was able to focus on it was right on, but it wouldn't focus, even in natural light, on things like newsprint, bricks, things that you would expect to be ideal subjects. If I took 3 or 4 pictures of the same thing, re-focusing each time, it would eventually stumble onto the right focus but there was no "middle of the road" or "sort of" focused. It was either (rarely) dead on, or wayyyyy off. Fortunately, as I said, it came from B&H and they e-mailed me a pre-paid shipping label and gave me the option of waiting until they received it to ship another, or shipping another one today (over night at that, as I had received the first one that way) and then crediting my CC when they received the return. I have never had anything but OUTSTANDING service from B&H!
03-31-2009, 10:34 PM   #15
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i got a focus screen today and its wonderful - so ill be running some more tests.
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