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03-30-2008, 05:16 AM   #1
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K20D Front Focusing Issues

G'day all,

I purchased my K20D last week and so far have been impressed. After playing around tonight with it I suspected there may be some front focus issues. I downloaded the Focus Test Chart and sure enough it seems to be front focusing between 30mm & 40mm on all lenses tested. With the sharpest of the results almost always at 40mm. I tested the K20 with the 16-45, FA50 & Tamron 18-250 with identical results within this range. I also did the test on my K10 and it came up perfect. This is my first real issue with all of the equipment I have purchased so it leaves a little sour taste.

Is there any way I can resolve this issue myself or will I need it to be fixed or serviced through warranty. I'm in Australia and will be contacting CR Kennedy to find the best course of action. It would be nice if the store where I purchased from just did an exchange but it was a special order so I dont think that will happen, I'll be directed through warranty is mt hunch.

The biggest pain is that i'll be shooting a wedding next week and if the camera goes off for service I won't get it back in time. Some consolation is that 30-40mm won't make hardly any difference to the wedding shots I will take.

Any experiences, advice and suggestions would be greatly appreciated.

Cheers,

Matt

03-30-2008, 05:24 AM   #2
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I thought the K20D had a lens "matching" option that could store up to 10 profiles?

This is used to eliminate such problems.
03-30-2008, 05:56 AM   #3
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I've read the manual and applied the fixes. I tried both options for individual and apply to all. I took the slider all the way to -10 to take the focus backward. It did make some very slight improvement but the sharpest part of the image remains between the 30-40mm range on all lenses. The most noticable difference was with the FA50 @1.4 the improvement was 20mm but the focus was still 20mm off the acceptable range. Unlucky for me the slider doesn't go all the way to -20 otherwise i'd be OK!
03-30-2008, 01:13 PM   #4
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Hi
I have the same problem with my k20d. I bought it a cople of weeks ago and when I shot with kit lens, it seemed OK, but then I bought 24mm/f1,8 Sigma and there was a problem to get focused shots.
After that I made focus tests and I found that my camera has front focus! I tried to adjust it thru custom menu and for kit lens the setting -8 was ok - auto fokus now worked properly. But for sigma I tried maximum adjustment -10 and there still was about 6mm front focus!
Last friday I took my camera back for waranty service. But they said that I have to wait for camera about 3 weeks because there isn`t pentax service center in Latvia and they have to send my camera for service to Germany.
Now I have only my old Canon S3IS point-and-shot camera

03-31-2008, 07:33 AM   #5
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Any sample photos to show for the supposed FF for real objects (not the test chart)?
04-01-2008, 10:54 AM   #6
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QuoteOriginally posted by RiceHigh Quote
Any sample photos to show for the supposed FF for real objects (not the test chart)?
There are sample photos from Sigma 24mm@f1,8
Attached Images
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PENTAX K20D  Photo 
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PENTAX K20D  Photo 
04-02-2008, 06:46 AM   #7
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I think there are two more things to note, which could cause AF errors:

1. The AF sensitivity area is larger than the red illumination mark and actually it is as large as the Spot metering bracket for the central AF point;

2. The AF sensor may not be perfectly aligned against the viewfinder mark

A full illustration for the case can be found here: RiceHigh's Pentax K100D Full Review

I suggest to do the AF test on a flat object (instead of on an inclined large object), which should be parallel to the film plane of your camera (i.e., perpendicular to the lens' optical axis), then you can know if there is really any focusing error, or not. An example of an AF accuracy test on flat objects can be seen below:

Pentax *ist DS AF Dependency on Kelvin & Exposure Value
04-02-2008, 06:04 PM   #8
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The best way to test for Front or Back focus is to pick a flat object, fill it up the whole frame then shoot. It's almost like a newspaper shot.

Today I just do a newspaper shot (not exactly newspaper) for the 1st time. And I found out that my K20D has front focus issue with all of my lenses. Usually, I do manual focus so I didn't notice this problem. I proceed to do the AF adjust on the camera for each lens. Magically, I just need to dial -10 and all of them were fixed.

These are the sample shots before and after on my FA* 85

Test Subject:



Quick Eye-Ball Manual Focus:



Autofocus before Adjustment:



Autofocus after Adjustment:



I have a few more lenses to go, but so far so good. The DA* zoom is fixed for all focals.

Edit: The DA 12-24 turns out to have Back-Focus instead. So I dial +5 and things work just fine.


Last edited by aegisphan; 04-02-2008 at 06:43 PM.
05-12-2008, 09:20 PM   #9
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aegisphan,

I discovered the exact same thing tonight. I guess I never noticed it in pictures because DOF was adequate. -10 adjustment on all my lenses nailed it perfectly. I am glad the k20d has this adjustment. If anything, I wish it were larger (just in case). I don't know if that is something that could be added to a firmware upgrade.
05-13-2008, 02:40 AM   #10
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-10 with all lenses

was an issue with my first K20D, it was replaced under warranty in 2 days (kudos to local Pentax guys :-). My K20DMkII is almost spot on (various lenses have +- small adjustments).
Best and happy tweaking, JR
05-13-2008, 02:37 PM   #11
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Strange, when I first posted about my 35mm F2 FFing on dpreview they said I was seeing things, now that it has a -6 adjustment it's perfect, some other lenses needed a +8 to -7 to get working right.

I'm just glad they put the af adjustments in the cam. I'm sure with sample variations some probably BF rather than FF but all in all unless you run out of adjustments you can fine tune every lens to be perfect.

BTW msot FF or BF issues seem only to apear on subjects past 10 ft or so, almost every lens I tried at first focused correctly spot oon up to 5ft and on some charts won't be noticed unless you go a bit farther.
05-17-2008, 01:08 AM   #12
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OK, I officially hate that focus chart test. I followed it to "perfection." As posted before it said all my lenses were front focussing, so I made the adjustment in my k20d. Well what do you know, I was shooting my daughters recital tonight, and the camera started back focusing, so I turned the adjustment back off.

Anyone else have similar problems with the test chart?
05-17-2008, 03:09 AM   #13
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So what could we do if we need more than -10 and/or +10 adjustment on the focus settings? Is pentax able to calibrate the k20D to get say -15 or +25?
05-17-2008, 09:18 AM   #14
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QuoteOriginally posted by PentaxPoke Quote
Anyone else have similar problems with the test chart?
I am suspicious with the test chart. For one because of the 45 inclination (I know the arguments why it should still work...), for another because of the relatively short distance.

What about a correction bracket (21 images corrected from -10 to +10) of a test chart hanging off a wall? Does it give you different results from the test chart? I am really curious to know.
05-17-2008, 09:21 AM   #15
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QuoteOriginally posted by RiceHigh Quote
The AF sensitivity area is larger than the red illumination mark and actually it is as large as the Spot metering bracket for the central AF point;
RH has a valid point here. A camera will always seem to frontfocus on a subject like this. Because there are nearer objects with high enough contrast within the center sensor's (relatively large) area.
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