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12-02-2011, 03:29 PM   #226
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Great thread. I have some Contax screens FS-1 -4 and -6. They work fantastic on a contax, could it work on the K5? I am thinking of converting the FS-1, with a microprism center.

Contax screens linkhttp://www.mir.com.my/rb/photography/hardwares/classics/contax/contaxrts2/manual/index5.htm

12-03-2011, 02:26 AM   #227
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QuoteOriginally posted by DogLover Quote
You might try 2 of the thin ones, if they are even usable without the thick one.
That's what I had to do. Took some attempts to get them placed straight but it's not too tricky.

I might try to replace one of the shims with some strips of tape later on if more fine tuning is needed.
12-03-2011, 03:52 AM   #228
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QuoteOriginally posted by lammie200 Quote
Anyway, I am just interested if anyone has more info about installation tips.
Original Pentax screen is ca 1.33mm (measured very carefully in plastic 0.12mm bag (for protection) by micrometer, so there could be some mistake) Katzeye is for example ca 1.63mm, didn't measure ee-S, but should be slightly thinner than Katzeye. So there is difference of ca 0.3mm, (almost visible, if you put them side by side). You have to compensate this difference with the thinner shim.

Thinner screen+shim=back focus, thicker shim+screen=front focus
Focusingscreen delivers 3pcs of 0.15mm shim and 1pc of 0.25mm. The original shim in K5 or K7 is 0.40mm ( at least in mine K7 and K5).
So you can combine them. Good method is to compare focus with the original pentax shim and without any shim. If the focus changes from front to back almost symetrically, then the right new shim has to be ca one half of 0.40mm.

EDIT: I corrected myself in post #230

Last edited by Jan67; 12-03-2011 at 07:30 AM.
12-03-2011, 05:28 AM   #229
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QuoteOriginally posted by Jan67 Quote
Thinner screen+shim=back focus, thicker shim+screen=front focus
Focusingscreen delivers 3pcs of 0.15mm shim and 1pc of 0.25mm. The original shim in K5 or K7 is 0.40mm ( at least in mine K7 and K5).
So you can combine them. Good method is to compare focus with the original pentax shim and without any shim. If the focus changes from front to back almost symetrically, then the right new shim has to be ca one half of 0.40mm.
OK, here is what may be a stupid question, but on what side is the point of focus of the screen? I tested a half dozen screens on my K20d and all of them gave proper focus, though some needed shimming to not rattle. The Chinese cut K1000 screen from Jinfinance I use now in that camera is dead on, though it is thicker than the original screen and no shims were added or removed. From that experience, I assumed the focus was on the bottom, but perhaps I was just lucky.


Last edited by GeneV; 12-03-2011 at 09:35 AM.
12-03-2011, 07:26 AM   #230
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QuoteOriginally posted by GeneV Quote
OK, here is what may be a stupid question, but on what side is the point of focus of the screen?
I have to correct myself.
Ground glass surface, used for focusing is located on the top of the focusing screen in Pentax DSLRs. So thickness of the screen can't play a role. L1 path (which ends at top of the screen, not bottom) can be influenced only by the shim.




It was already discussed several times on this forum:
--The things you learn. Katz Eye screen--
12-03-2011, 09:07 AM   #231
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I reread --The things you learn. Katz Eye screen-- and notice I actually posted in that old thread, but I guess I've slept about 500 times since then. I am the one who needed to correct my understanding--again.

If the factory shim is in the top, and the top of the focus screen (next to the pentaprism) is the point of focus, then what is happening with my Jinfinance screen in the K20d must be that with the same shim there, the focus distance is the same and the retaining frame is just being sprung a bit by the thicker screen.

It would seem that the top shim should stay the same for all screens if the focus was right originally. The only issue with a thicker screen than the Pentax is how it fits in the drop-down frame which holds it up there. A thinner screen could change the focus if it weren't shimmed from the bottom and lay there with its matte side not contacting the shim and closer to the mirror. Or again, am I missing something?

Last edited by GeneV; 12-03-2011 at 10:43 AM.
12-03-2011, 10:40 AM   #232
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Paunel wrote on another thread "K5 focusing screen":

Thanks, Quicksand!
But I must say mr. dlacouture, the thickness is important. The optic "way" from the mirror reflexion till the upside matte screen focus surface must be kept to the same value as before changing the screen. This way has 2 components: one in the air (d1) and one in the plastic glass of the screen (d2). Optic way is d1+ n*d2 where n is the optic index of the refractive screen (about 1.5 for perspex). If the new screen has a major thickness than the old one, the new (d1) must be decreased to preserve the sum. That means need for shim of the difference: old (d1)-new(d1). But if the new screen is thinner than the old one, it must be positioned upper (closer to the pentaprism) and if there are no shims to be removed (with the needed correction) is no chance to obtain a good focus. This explain the different results on the forum regarding the change of the focus screen.
For exemple the old screen thickness is 1.3mm and the new one is 1.5mm. The optic difference is (1.5-1.3)*1.5[refractive index]=0.2*1.5=0.3mm. You must compensate adding shim(s) of total thickness of 0.3mm.
The downside surface of the screen is a Fresnel lens (a plane lens) and if the focus length is different changing the screen then is a change in the resulted exposure because more or less light is distributed on the exposure sensor in the front of the pentaprism. The Katzeye screen with optic coating (like the lens coating) is more luminous and the result is an underexposure that must be compensated in camera. But if exist also the effect of different focus of the Fresnel lens the compensation can be in every sense (over or under). This must be tested, I only give you a simple theory implied in this process.
And, to prevent various "observations" here, I must say I'm licensed in physics.
12-03-2011, 02:04 PM   #233
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QuoteOriginally posted by WWWench Quote
A sane method, is to create a DXF file in AutoCad or any 2d vector application. A trivial job using only offsets, lines and a radius entry.
Do you have such a file, and would kindly share it with us maybe? :-)

12-03-2011, 02:08 PM   #234
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Thanks for the explanation. Finally I know the right reason for different shims.
12-03-2011, 03:12 PM   #235
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QuoteOriginally posted by Alcazar Quote
Do you have such a file, and would kindly share it with us maybe? :-)
If you have the exact dimensions I could make a DXF file in Illustrator.
12-03-2011, 03:25 PM   #236
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Screens for K7-K5 17,9 mm.x 26 mm.

Picture will not show, try the link for drawing: http://www.bhphotovideo.com/bnh/controller/home?O=ProductDetail&A=showItemLa...=640680&is=REG

Last edited by Pontax; 12-03-2011 at 03:32 PM.
12-03-2011, 06:14 PM   #237
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Here's a link to the file. The B&H link provided didn't work, so I went to the site and got a screen capture of an M60 screen and scaled it to the dimensions given. It was only low res, but I was only using it for the radius of the corners (which it turns out weren't rounded, but only beveledóconfirmed by checking a Katz Eye I had lying around) and position and size of the tab, which I don't think is hyper critical. The result is a dxf file of 26 x 17.9mm. Here's hoping that it is of use to you.

If someone has access to an AutoCad program, I'd appreciate a double check. When I open the dxf file back up in Illustrator it doesn't come in at the right size. I know the file was built properly but I don't know if the size is going bad when I export from Illustrator or when I bring it back in. If EPS files are usable, that might be a preferred option. I've included an EPS file as well.

Focus Screen.zip
12-04-2011, 02:20 AM   #238
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Sorry that the link did not work, it did not work either for dlacouture (the founder of this thread).

The eps. file looks great, I will presented to my friend who works at are place, which has are CNC laser cutter. Maybe water jet is better or a router?

Can't open the dxf. file
12-04-2011, 05:18 AM   #239
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QuoteOriginally posted by G_Money Quote
If someone has access to an AutoCad program, I'd appreciate a double check. When I open the dxf file back up in Illustrator it doesn't come in at the right size. I know the file was built properly but I don't know if the size is going bad when I export from Illustrator or when I bring it back in. If EPS files are usable, that might be a preferred option. I've included an EPS file as well.
I opened the .eps file, matches your dimensions and is in 1:1 scale. I couldn't open the .dxf, but it could be my program.

T
12-04-2011, 06:36 AM   #240
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QuoteOriginally posted by G_Money Quote
Here's a link to the file. The B&H link provided didn't work, so I went to the site and got a screen capture of an M60 screen and scaled it to the dimensions given. It was only low res, but I was only using it for the radius of the corners (which it turns out weren't rounded, but only beveledóconfirmed by checking a Katz Eye I had lying around) and position and size of the tab, which I don't think is hyper critical. The result is a dxf file of 26 x 17.9mm. Here's hoping that it is of use to you.

If someone has access to an AutoCad program, I'd appreciate a double check. When I open the dxf file back up in Illustrator it doesn't come in at the right size. I know the file was built properly but I don't know if the size is going bad when I export from Illustrator or when I bring it back in. If EPS files are usable, that might be a preferred option. I've included an EPS file as well.

Focus Screen.zip

I opened the dxf , it measures 26.0002 mm x 17.8999 mm and the sides are perpendicular (measured at 90.0000degrees)

The 4 chamfered corners aren't absolutely perfectly uniform (~ < 0.1mm out) but this shouldn't make a difference
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