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03-18-2013, 03:55 PM   #1
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Shimming focus screens (+/-)

I have a question for those of whom have replaced their stock focus screens with any third party focus screens that required shimming.

I've replaced the focus screens on the K20D but did not require shimming but the KatzEye focus screen for the K-5, do need shimming. I am trying to save some unnecessary work: The AF focus indicator lights up but the split prism do not line up. I need to turn the focus very slightly towards the MFD side, do I need to add or subtract shim from or to the focus screen to align the focus indicator with the split prism?

Thanks,

03-18-2013, 04:15 PM   #2
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QuoteOriginally posted by excanonfd Quote
I have a question for those of whom have replaced their stock focus screens with any third party focus screens that required shimming.

I've replaced the focus screens on the K20D but did not require shimming but the KatzEye focus screen for the K-5, do need shimming. I am trying to save some unnecessary work: The AF focus indicator lights up but the split prism do not line up. I need to turn the focus very slightly towards the MFD side, do I need to add or subtract shim from or to the focus screen to align the focus indicator with the split prism?

Thanks,
What I suggest is to totally ignore the focus indicator light, it is not accurate at all.
do your calibration on a tripod, and use live view to confirm focus, then check each pic at full size on your monitor. Once your happy with that, check what the split prism is doing, and shim it until it is even. I found with my K5 that I needed to use a piece of tape for a shim as the supplied ones were either too thick or too thin...

I hope that helps

Cheers

Chris
03-18-2013, 06:14 PM   #3
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The AF focus indicator is not affected by the focus screen. If what you see in the viewfinder matches what you get in output, the focus screen is aligned correctly. (You may have to try different apertures to find the one that most closely matches the DOF of the screen.)
03-18-2013, 07:06 PM   #4
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With any camera brand, if I could afford to I'd just pay someone to zero my screen period. If I hit the lottery I'd buy some new things and send my familiar ones off to be calibrated. New cameras expect us to accpt optical margins of error. Fact is, I think they could leave the AF off entirely if they'd just make the finder accurate. (This is why I never touched an AF camera since Canon switched mounts. Why bother.) Even at my age it's faster to just do it myself than tell a compuer what to do.

I mean, I finally got a chance to handle a fairly modern camera, even by digital standards. It'll maybe focus on the wrong damn thing in milliseconds. And I'm like, 'IThank you for your input but I'm trying to get a shot here.'


Last edited by Ratmagiclady; 03-18-2013 at 07:16 PM.
03-18-2013, 08:14 PM   #5
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Obviously the output is not matching up with the split prism screen in the viewfinder, hence my question. Shots taken with AF indicator whether with AF or MF lens, are sharp enough in my eyes. The same shot when viewed in the viewfinder, the split prism do not match up. I have to physically turn the focus ring slightly towards MFD to make the split prism match up. This is the case with every lens I have shot so far, indicating to me the split prism viewfinder is not aligned properly with the true focus point.

Do I need to add more shims or subtract the shims when the apparent focus as indicated by the split prism is in front of the true focus point?

Thanks,
03-18-2013, 08:22 PM   #6
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The Katz Eye aligns to the same plane as your original screen. In all likelihood, the original was not properly colimated. Having properly assigned blame, you now want to calibrate your screen against live view using a magnifying loupe, not the AF system. The AF system is much less precise than the split image on your Katz Eye. Another option is to download one of those moire' targets to use with Live view.


Steve

(...have remained very glad that my Katz Eye did not require any adjustment...)
03-18-2013, 11:09 PM   #7
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QuoteOriginally posted by stevebrot Quote
The Katz Eye aligns to the same plane as your original screen. In all likelihood, the original was not properly colimated. Having properly assigned blame, you now want to calibrate your screen against live view using a magnifying loupe, not the AF system. The AF system is much less precise than the split image on your Katz Eye. Another option is to download one of those moire' targets to use with Live view.


Steve

(...have remained very glad that my Katz Eye did not require any adjustment...)
That's what I thought too, the KatzEye focus screen for the K20D had no issues at all with focusing. Having acquired a used K-5 and a KatzEye screen for the K-5, I figured 'drop it in and shoot'... Oh well, I guess I am going to have to go through with this tedious testing process if I want to get the most out of the camera.

03-19-2013, 02:18 AM   #8
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I got a set of shims from pentax US, the process had been around 2 hrs, with several time changing.
Be careful when you pickup the katzeye. Dust also a factor. I tested the shims first, then when it is ok, I open up and clean the dust.

Asking Katzeye support, they claim that their screen should not require any shim. Guess they never installed one themself.
03-19-2013, 04:43 AM   #9
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QuoteOriginally posted by excanonfd Quote
Do I need to add more shims or subtract the shims when the apparent focus as indicated by the split prism is in front of the true focus point?
Add shim.
03-19-2013, 01:27 PM   #10
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QuoteOriginally posted by baro-nite Quote
Add shim.
The previous owner of my K-5 must have removed the shim because there was none inside. I am in the process of trying to obtain some from Pentax Canada.
03-19-2013, 03:00 PM   #11
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Strips of Post-It make a reasonable temporary solution.
03-19-2013, 07:35 PM   #12
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QuoteOriginally posted by baro-nite Quote
Strips of Post-It make a reasonable temporary solution.
Thanks, that might be the route I have to take if I don't hear from Pentax Canada soon.
03-19-2013, 08:24 PM   #13
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QuoteOriginally posted by excanonfd Quote
The previous owner of my K-5 must have removed the shim because there was none inside.
Considering that manufacturing tolerances aren't perfect, it makes sense to plan the specifications such that a 'medium' shim is normal. With that scheme, shims may be added for either a plus or minus correction as needed. If no shims were the original design goal, adding shims could only correct in one direction. That's not an efficient or economical design.

I'm always suspicious that either someone didn't understand the instructions for screen manipulation/exchange or that the camera was a initially a marginal assembly of out of tolerance parts at 'birth' if no shim is found on first inspection of the screen.

H2
03-20-2013, 09:44 AM   #14
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same but opposite problem

QuoteOriginally posted by excanonfd Quote
Obviously the output is not matching up with the split prism screen in the viewfinder, hence my question. Shots taken with AF indicator whether with AF or MF lens, are sharp enough in my eyes. The same shot when viewed in the viewfinder, the split prism do not match up. I have to physically turn the focus ring slightly towards MFD to make the split prism match up. This is the case with every lens I have shot so far, indicating to me the split prism viewfinder is not aligned properly with the true focus point.

Do I need to add more shims or subtract the shims when the apparent focus as indicated by the split prism is in front of the true focus point?

Thanks,
With my old ME super screen I have to turn slightly away from MFD. I would really like to get this aligned: anyone help with obtaining shims in UK??? I know I need a thinner shim so excanonfd you certainly need a bit more...NB when I first installed mine it wasn't quite seating perfectly and resulted in same problem - check that!
BTW just acquired an original Asahi 2x viewer magnifier
http://www.tremyfoel.co.uk/photography/PentaxViewer3-800.jpg
my initial impressions of this are good but now I really need to get the shim issue sorted
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