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12-10-2008, 11:14 PM   #1
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K20D- more ff/bf issuses question

I recently received my K20D and never tested it until tonight.
The test constisted of 4 lenses. 77 limited, Sigma 105 macro, tamron 28-75 and Voigtlander nokton. This is the first time I have ever done a test like this so this is why I am asking questions. Did I do something wrong, how to test properly?
Tungsten light.
77 seems to focus properly, mabey very slight ff, Sigma the same. tamron very severe ff, same for the Voigtlander.

I set the camera on tripod at an angle ( not measured ) and used Nikon d70 test focusing chart. Of cousre 3 of the lenses tested are AF and I used Af for the test with these lenses.

I also tested lenses on my K10D and all focused properly.

My big concern is the Voigtlander manual focus. this would show that it is not AF system at fault wouldn't it?

I know I should do more thorough testing I guess. But how should \I proceed from here.
Thanks
Oren

12-10-2008, 11:40 PM   #2
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My K10D will front focus with tungstone light, or any light that has a high infrared component.

You might want to try the focus test in daylight.
12-11-2008, 12:04 AM   #3
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Same for me as KungPow. Test your camera in daylight or flourescent, tungsten has a tendency to confuse my K20D.
12-11-2008, 12:32 AM   #4
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Is there any downloadable charts and guides that show you how to do this properly.
Also is there a guide for adjusting the ff/bf in camera to suit different lenses.
I have read that this can be done but don't know how.
I have a K20D with a Sigma 17-70, 2.8-4.5 lens, I think it has good focus but would
like to check just to be sure that its correct.

12-11-2008, 01:16 AM   #5
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QuoteOriginally posted by ozzi-paul Quote
Is there any downloadable charts and guides that show you how to do this properly.
Also is there a guide for adjusting the ff/bf in camera to suit different lenses.
I have read that this can be done but don't know how.
I have a K20D with a Sigma 17-70, 2.8-4.5 lens, I think it has good focus but would
like to check just to be sure that its correct.
My recommendation is to forget about the chart (it has inherent flaws when used with Pentax AF IMHO), and set up some objects (I use DVD cases - something with print and a planar surface) on a table like this..

top view looking down.
\
| <----------------------------------------camera
\
This gives you a planar surface to focus on and easily shows FF/BF tendencies.

Here's an example shot although this was not very usable as there was so much glare from the window on the right...
12-11-2008, 01:21 AM   #6
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So if a camera (k20d) is found to be out, what is the best method of adjustment.
12-11-2008, 01:44 AM   #7
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QuoteOriginally posted by heliphoto Quote
My recommendation is to forget about the chart (it has inherent flaws when used with Pentax AF IMHO), and set up some objects (I use DVD cases - something with print and a planar surface) on a table like this..

top view looking down.
\
| <----------------------------------------camera
\
This gives you a planar surface to focus on and easily shows FF/BF tendencies.

Here's an example shot although this was not very usable as there was so much glare from the window on the right...
I like the idea of this method. I'll give it a try tmw. Everytime I use a focus chart I get different results??? Thanks for sharing Josh
12-11-2008, 06:30 AM   #8
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Thanks for replys,
I had heard tungsten light was a problems with the Af system but why is the Voigtlander FFing.
We have a shortage of sunshine at the moment so I might have to purchase a different light. What about using flash?

I see someone likes South Park I will have to try this method also.
Another concern is that the camera is new so I don't have that long before I have to send it back for replacement. But I don't want ot send a perfectly good camera back.

ozzi-paul, there is AF adjustment in the menu. I played around with this but even -10 didn't do it.
Of course I couldn't adjust the manual focus Voigtlander. So again, does the light make a difference when manual focusing?

12-11-2008, 09:58 AM   #9
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QuoteOriginally posted by OrenMc Quote
Thanks for replys,
I had heard tungsten light was a problems with the Af system but why is the Voigtlander FFing.
We have a shortage of sunshine at the moment so I might have to purchase a different light. What about using flash?

I see someone likes South Park I will have to try this method also.
Another concern is that the camera is new so I don't have that long before I have to send it back for replacement. But I don't want ot send a perfectly good camera back.

ozzi-paul, there is AF adjustment in the menu. I played around with this but even -10 didn't do it.
Of course I couldn't adjust the manual focus Voigtlander. So again, does the light make a difference when manual focusing?
I'm guessing you might be better off sending it back - or in for warranty work (don't know your time constraints). From what I've read - if just the AF was off, it would point to the AF system, and if just the viewfinder focus was off it could be the shimming of the focus screen, but if their both off, it could be that the light is traveling a different distance to the viewfinder and focus sensor than to the sensor... I don't remember where I read that, or what the causes might be - sorry.

I wouldn't think the light would matter for MF, but I could be wrong.
12-11-2008, 10:19 AM   #10
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QuoteOriginally posted by ozzi-paul Quote
Is there any downloadable charts and guides that show you how to do this properly.
Also is there a guide for adjusting the ff/bf in camera to suit different lenses.
I have read that this can be done but don't know how.
I have a K20D with a Sigma 17-70, 2.8-4.5 lens, I think it has good focus but would
like to check just to be sure that its correct.
A chart many people like is at focustestchart.com, but I don't like using it that much. Part of the problem is that I read in this thread and elsewhere that you should use a distance of about 5 feet (1.5m) when testing focus, but using that chart with a wide angle lens at 5ft., it's impossible to be sure whether you've locked the sensor on the "focus here" line or one of the other lines on the chart which would render the results worthless.

To make changes to the focus adjustment in the K20D, go to the custom menu, and on option 35 change the setting to 'on', and you'll end up in the adjustment menu. Apply All changes the adjustment across the board for all lenses, while Apply One will remember that model of lens and apply the adjustment to that lens only. Personally I adjusted each lens using apply one, 'till I found that all of them needed around -7 on my camera, so I made -7 the default and then changed the "apply one" to 0 or +1 or -1 as necessary for each lens. That way when I get a new lens, it will be close to right out of the box because the -7 seems to relate to my camera.
  • Higher adjustment numbers (+) move the focus closer to the camera
  • Lower adjustment numbers (-) move the focus farther away.

So my camera front focus by default, so -7 moves the focus point further away about the right amount.
12-11-2008, 08:45 PM   #11
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Thanks again heliphoto,
I'm just a little frustated because I don't have the time and the light I would like. I will be alright in the end though. It may just take a little extra effort but I am sure there is something to learn thru all this.

I will get back and share my results.
12-11-2008, 10:53 PM   #12
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QuoteOriginally posted by OrenMc Quote
I had heard tungsten light was a problems with the Af system but why is the Voigtlander FFing.
Because the focus screen is incapable of showing you DOF as shallow as you are actually getting, meaning there wil be things that look in focus in the viewfinder but not in the picture, and you are therefore not necessarily focusing on what you think you are focusing on. Basically, the rear of the apparently-in-focus zone will end up OOF, so the center of the in-focus zone will appear to have shifted forward.

QuoteQuote:
So again, does the light make a difference when manual focusing?
I'm not sure if there is anything physical going on, but my perception is that in poor light, I'm more likely to focus such that things in front of the subject are in focus as much as my subject. Meaning the center of the apparently-in-focus zone may be in front of the subject. Whereas the issue I mentioned above suggests that one should be trying to make things *behind* the subject appear in focus - that is, to keep the center of the apparently-in-focus zone behind the subject, so that when it shifts forward on taking the picture, all is well.
12-12-2008, 05:41 AM   #13
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QuoteOriginally posted by OrenMc Quote
Thanks for replys,
I had heard tungsten light was a problems with the Af system but why is the Voigtlander FFing.
We have a shortage of sunshine at the moment so I might have to purchase a different light. What about using flash?
Definitely do your testing under natural and artificial light. You don't need sunshine, you just need a bit of daylight from the window and no other light source. You're on a tripod, so you don't have to worry about shutter speeds.

In your testing, also check the effect of aperture. I found a front-focus issue in tungsten light, that was severe at F1.4, slight at F2.8 and gone at F4 with all four lenses. The front focussing was present with manual and auto focus in tungsten light, and none of the four lenses tested had a problem in natural light at any aperture. Have a look at this thread, https://www.pentaxforums.com/forums/pentax-dslr-discussion/42773-front-focusing-done-death.html, and especially this post https://www.pentaxforums.com/forums/408527-post24.html.
12-19-2008, 02:18 PM   #14
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Just an update. I was able to get out today and take a couple shots with some sunshine.
I forgot that I had set the camera AF adjust -5 and when I took the first shot I said to myself
" S*#T, now its BFing ", then I checked the AF adjust.

Tungsten light is not a good idea for running tests!!

Camera set at -5 AF adjust


Reset to 0


I don't think I like the focusing chart either.



I'm a happy camper now.

Last edited by OrenMc; 12-19-2008 at 05:27 PM.
12-19-2008, 04:53 PM   #15
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I just received my K20D yesterday and ran some lens bf/ff tests today. One surprising result (as least to me) was how my (older version) Sigma 70-200mm f2.8 focused. It front focused at 200mm and back focused at lesser focal lengths. I'm still trying to figure that one out. Do I need to send the lens to Sigma for servicing?
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