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07-09-2008, 10:50 AM   #1
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Pentax DSLR focusing screen

Hello,
Does anyone know what the thickness of the focusing is, or could measure a spare screen? I have a couple FF screens from other brands that I would like to rework, but I would like to check the thickness before I pull my screen out. Also here is a good site with instructions on modifing a FF screen for Pentax.

Dave

K10D, new split focusing screen - a set on Flickr


Last edited by Big Dave; 08-10-2008 at 03:44 PM.
07-09-2008, 11:07 AM   #2
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i can tell you the dimensions of a K100D screen....
07-09-2008, 12:13 PM   #3
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I believe it is 1.42 mm for K10D.

Reference: Some seller in ebay selling split focus screen and he was claiming that the normal ones on ebay for Pentax are 1.8mm thick whereas Pentax uses 1.42mm. So the one he supplies are the modified K1000 focus screen which is between 1.35~1.37mm.

Cheers
Nish
07-09-2008, 03:50 PM   #4
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Nish,
That is very useful information. It make me think that the performance differences between sources may be due to slight errors in screen position, due to screen thickness. A thin shim may be necessary with some screens to produce accurate focus. Very interesting.

Dave

QuoteOriginally posted by bnishanth Quote
I believe it is 1.42 mm for K10D.

Reference: Some seller in ebay selling split focus screen and he was claiming that the normal ones on ebay for Pentax are 1.8mm thick whereas Pentax uses 1.42mm. So the one he supplies are the modified K1000 focus screen which is between 1.35~1.37mm.

Cheers
Nish


07-09-2008, 05:46 PM   #5
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QuoteOriginally posted by Big Dave Quote
Nish,
That is very useful information. It make me think that the performance differences between sources may be due to slight errors in screen position, due to screen thickness. A thin shim may be necessary with some screens to produce accurate focus. Very interesting.

Dave
Dave, I know that some of the "Hong Kong" screens being sold come with shims because they're too thin. Good luck with getting the screen "right"!!
07-09-2008, 07:41 PM   #6
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Thanks for the tip Chip. Dave

QuoteOriginally posted by ChipB Quote
Dave, I know that some of the "Hong Kong" screens being sold come with shims because they're too thin. Good luck with getting the screen "right"!!
07-09-2008, 07:54 PM   #7
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Big Dave:


I just measured my original screen for my K20 with a digital micrometer--it is 1.4mm thick, precisely.

I have the screen out because I changed to a split focus prism, one from China. If I recall correctly, from the research I did, the K20 screen is the same thickness but please verify this. Good luck.



Regards,

Ernest
07-09-2008, 11:41 PM   #8
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Jewelltrail, could you measure other two dimensions of the K20 original focusing screen?

07-10-2008, 01:41 AM   #9
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After looking at the flickr tutorial it seems that he did not bother to replicate protruding tabs on the K10 screen. For what purpose are those? Probably positioning. Does that mean that reworked screen could posibly move inside?
07-10-2008, 04:07 AM   #10
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QuoteOriginally posted by Big Dave Quote
Nish,
That is very useful information. It make me think that the performance differences between sources may be due to slight errors in screen position, due to screen thickness. A thin shim may be necessary with some screens to produce accurate focus. Very interesting.

Dave
Yes, you would need a shim if you use modified K1000 screen. However many users have used 1.8mm thick Chinese screens and as a result they have lost some brightness on their viewfinder, however they claim that this loss of brightness can be managed with.

I believe the thickness also affects your metering, but not sure,

Cheers
Nish
07-10-2008, 04:35 AM   #11
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I ordered mine from Focusing Screen and will receive it from Singapore next week normally.

Focusing screen don't affect AF. But from the site, there is some difference regarding specifications between K10D and K20D.
07-10-2008, 06:05 AM   #12
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QuoteOriginally posted by Big Dave Quote
Hello,
Does anyone know what the thickness of the focusing is, or could measure a spare screen? I have a couple FF screens from other brands that I would like to rework, but I would like to check the thickness before I pull my screen out. Also here is a good site with instructions on modifing a FF screen for Pentax.

Dave

K10D, new split focusing screen - a set on Flickr
I suggest if you have the full confidence, detach your original screen and measure it by a precision ruler.

But it should be noted that different "focusing" screen will affect the accuracy of the light meter, as well as the accuracy of manual focus at the matte area too. For details of some of those cases, read this:-

RiceHigh's Pentax Blog: When the Focusing Screen Lies (for Focusing and Metering)
07-10-2008, 10:51 AM   #13
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QuoteQuote:
gamgee: "Jewelltrail, could you measure other two dimensions of the K20 original focusing screen?"
I measure 25.1 mm for the length, and 17.5mm for the width--not counting the extra width the locating tab would add.

My split prism begins to darken even at f5.6, forcing me to focus at large apertures. I bought from a seller who was recommended by others in this forum. The split prism screen did not come with a shim.

Regards,

Ernest
07-10-2008, 12:37 PM   #14
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Thanks Rice, Your information is very helpful. Dave

QuoteOriginally posted by RiceHigh Quote
I suggest if you have the full confidence, detach your original screen and measure it by a precision ruler.

But it should be noted that different "focusing" screen will affect the accuracy of the light meter, as well as the accuracy of manual focus at the matte area too. For details of some of those cases, read this:-

RiceHigh's Pentax Blog: When the Focusing Screen Lies (for Focusing and Metering)
07-11-2008, 04:35 AM   #15
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QuoteOriginally posted by Big Dave Quote
Thanks Rice, Your information is very helpful. Dave
You're welcome :-)
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