[ytterbium]

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First of all i choose a bad time to replace the screen. Early morning, before breakfast. This resulted in my hands shaking a little in the beginning.
First thing i could not get the screen holder to unlock. It had to be pushed in different direction than i imagined. Mirror damping foam was also obstructing access to focusing screen lock and received some pushing against it.
After few miserable attempts it accidentally popped open. Then i was surprised to see that under the focusing screen (near the mirror box) there is something like a shim (square "U" shaped metallic spacer). About 0.8mm tick.

Another scary thing was that the focusing screen is much less (almost not at all) constrained in the metallic frame than i expected. It easily moves to the sides, and slips over limiting metallic flaps falling in the mirror box or trough the lowered frame (hitting main mirror). Same goes for the weird shim. And since its metallic, every time it hit something it left a nasty scratch.
Because of this supplied finger condoms and tweezers is not sufficient to change the screen.
Another bad thing is if the shim gets a little free from being held by focusing screen it lets the frame open even more hitting main mirror.
After first install the circle was shifted to the side and up and was heavily covered with dust. Even after carefully vacuum-cleaning everything used as well as rocket-blowing.
After few trials with rocket blower and aligning i learned to successfully open the lock and move the screen without messing stuff. Ended up with one small dust (maybe just screen grain), screen centred horizontally (impossible to get it centred vertically, always stays a little too high even against frame edge) and few scratches on main mirror (not visible in viewfinder).
Pretty thrilling experience.

What questions are left?

Those who have installed Chinese focusing screens, have you managed to align them perfectly in center?

Does split prism has to be centred to correctly measure distance (at the point its pointing at if its not in the centre).
I believe that centring is more important to metering, because if the prism starts to black out you can move (centre) your eye, but the meter still get the blacked view.

What is that metallic shim in k200d between mirror box and focusing screen, should it be there?

What precision can you get/expect? I get a small front focus, should i get shims, where (links please, paypal, worldwide shipping)? It seemed like there was no protecting cover to be peeled of (the screen was in thin plastic bag, in a box).

Anyway i was pleasantly surprised, that visually it had the same brightness as original screen and even better in centre. Even without exact precision made much easier to get manual focus with in-camera confirmation.

[sinus007]

...First of all i choose a bad time to replace the screen. Early morning, before breakfast. This resulted in my hands shaking a little in the beginning.
First thing i could not get the screen holder to unlock. It had to be pushed in different direction than i imagined. Mirror damping foam was also obstructing access to focusing screen lock and received some pushing against it.
After few miserable attempts it accidentally popped open. Then i was surprised to see that under the focusing screen (near the mirror box) there is something like a shim (square "U" shaped metallic spacer). About 0.8mm tick.

Another scary thing was that the focusing screen is much less (almost not at all) constrained in the metallic frame than i expected. It easily moves to the sides, and slips over limiting metallic flaps falling in the mirror box or trough the lowered frame (hitting main mirror). Same goes for the weird shim. And since its metallic, every time it hit something it left a nasty scratch.
Because of this supplied finger condoms and tweezers is not sufficient to change the screen.
Another bad thing is if the shim gets a little free from being held by focusing screen it lets the frame open even more hitting main mirror.
After first install the circle was shifted to the side and up and was heavily covered with dust. Even after carefully vacuum-cleaning everything used as well as rocket-blowing.
After few trials with rocket blower and aligning i learned to successfully open the lock and move the screen without messing stuff. Ended up with one small dust (maybe just screen grain), screen centred horizontally (impossible to get it centred vertically, always stays a little too high even against frame edge) and few scratches on main mirror (not visible in viewfinder).
Pretty thrilling experience.

What questions are left?

Those who have installed Chinese focusing screens, have you managed to align them perfectly in center?

Does split prism has to be centred to correctly measure distance (at the point its pointing at if its not in the centre).
I believe that centring is more important to metering, because if the prism starts to black out you can move (centre) your eye, but the meter still get the blacked view.

What is that metallic shim in k200d between mirror box and focusing screen, should it be there?

What precision can you get/expect? I get a small front focus, should i get shims, where (links please, paypal, worldwide shipping)? It seemed like there was no protecting cover to be peeled of (the screen was in thin plastic bag, in a box).

Anyway i was pleasantly surprised, that visually it had the same brightness as original screen and even better in centre. Even without exact precision made much easier to get manual focus with in-camera confirmation.

Hi,
First, let me point out that I'm using katzeye w/optibright and like it very much.
The shim that you found behind the focusing screen should be 0.15mm thick. You can use them to adjust FF/BF for MF. They come in 5(?) sizes (thickness): 0.15mm, 0.20mm, 0.25mm, 0.30mm and 0.40mm. You can buy them from Pentax. In my case (I was guided by Rachael Katz) I found that 0.30mm (2 x0.15mm shims) provides the best focus. I could notice misfocus only at aperatures wider than 2.8, now focus is OK @1.4. Good enough for me: I don't have faster lenses.
I tried a chineese screen and found that the only advantage it has is the 45 deg split and the cost, of course. In my case it fit very tight into the tray and I had to play with the shims again.
Good luck with yours.

[Jewelltrail]

So sorry to hear about the problems with the screen install. I have a K20, which doesn't use shims, and the Chinese prism slipped right in--no problems. The frame for the screen both seats and centers it.

I'm not sure why you have centering problems. It could be you have the wrong sized screen, though I doubt it. If a shim came out of there, there is a good chance one needs to go back in there--it depends on the new screen's thickness. No problem though. Just measure the old and new screen with a micrometer. I would use one of those newer, plastic models on the screens. can get them cheap nowadays and they often come in handy==Sears has them, but even cheaper from large, no name tool warehouses, like Harbor Freight.

First, take a measurement of both screens' height and length--any difference here would explain the centering problem. Next, take a measurement of the width of both screens. If both screens are identical, then use the same shim. If the new screen is thicker, subtract the difference of the old screen and then you know what, if any, shim to use. And if the new screen is thinner, you know you need a shim. Just add the difference by which it is thicker to the original shim and you have the thickness for a new shim--order from Pentax. (edit:by use of the word "width," I mean the screen's thickness)

For example: new screen measures .8mm thicker than original screen--in this case you do not need a shim.]

Here are directions for installing a prism in the K200d--they are for the Katz eye, but obviously apply to other screens as well.



http://www.katzeyeoptics.com/files/install6.pdf

[octavmandru]

My humble opinion...
I have experience with cleaning one matte screen on an older camera, but is the same principle.
As I noticed on my camera the image is formed on the back of the screen (inside the prism). The screen is "matte" only on one side.

This means is not very important the thickness of the matte for the correct focus, but rather the exact positioning of the matte surface.
Normally, this is a constant value adjusted one time, when the camera is new, using the shim.

I understand you have problems aligning the screen left-right/up-down? Is the screen the same size as the old one?

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Last edited by octavmandru; 04-05-2009 at 09:15 PM.

[ytterbium]

Thank you for your responses.
I must agree with octavmandru, that the screen thickness dosnt change matted plane distance.
I can only estimate in which direction i have to adjust screen from infinity or auto focus.
I think the factory installed shim was just within the error margin for auto focus preview and composing, knowing that stock screen has more DOF.
When measurbating its even OK for split screen, unless your subject gets further than measurbation distances. Then you can get >1 meter front focus @ F1.8.

Anyway there is no place nearby where i could get/order shims nor can i find such place in Google. Any help would be appreciated.
I remember someone mentioning a shim kit...

Interestingly that every time i remove the screen i manage to reduce dust in screen and do less damage. Just checked if i haven't left some protective film or let any of the screen sides slip off the frame, thus moving a little away from focal plane. Btw. The frame securing screen seems a bit bent when released. Should it be perfectly flat or have some curvature (towards clip end)?

[Lowell Goudge]

somewhere, and I don't know the exact post anymore, these were mentioned as available through pentax.

I did not have an issue as I have a K10D. the split image went straght in and focusing is spot on.

the only complaint I have is that if anything, I think my metering on the K10D is worse now than with the standard screen,

Also, I find that with the jinfinance version i bought, the screen blacks out at F5.6 and you need to be carefully alligned at F4.

[ytterbium]

It gets darker at F5.6 and requires very good alignment at F8 but certainly dosnt black out. SHoot-ing version. At F9 i start to see aberrations and aligning eye becomes a pain.

What do you mean as available throgh Pentax. I dont see anything like shims listed in DSLR acessories. Closest thing i could find in Pentax store was tweezers:
PentaxWebstore - Viewfinders Accessories

It seems that it might be easier to try to make something on my own.

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Last edited by ytterbium; 04-06-2009 at 12:33 PM.

[Jewelltrail]

ytterbium: It seems that it might be easier to try to make something on my own

.

Pentax sells them, many people here have said so. Call the phone # in Golden, Colorado--I'm sure they will help you.


PENTAX Imaging Company
600 12th Street , Suite 300, Golden , Colorado 80401
tel: (1) 303 799 8000
fax: (1) 303 790 1131

[Jewelltrail]

Lowell Goudge: Also, I find that with the jinfinance version i bought, the screen blacks out at F5.6 and you need to be carefully alligned at F4.

My experience with the jinfinance screen. @ 5.6, is the screen just begins to lose its utility and I have to adjust my eye to compensate.

[Jewelltrail]

ytterbium: It seems that it might be easier to try to make something on my own.

Ytterbium, regarding focus screen shims, please read through thread if you have not already.


https://www.pentaxforums.com/forums/pentax-dslr-discussion/45309-shims-focus-screen-k10d.html

[ytterbium]

Seen that. As you can see from there, Pentax CO sends only to US. I need EU. Anyway i'm affraid that even if they could ship, sending would cost many times more than the shim itself.

Didnt noticed it before but there also was talk about DIY post-it shims being affected by humidity, so this is not an option.
I should use some thicker Aluminium foil i guess.
Btw i mailed jinfincance and asked about shims, he told me that they do not sell them but he might try to make some.

[Gooshin]

i would like to chime in with my personal experience completly unrelated to the digital and the chinese screens

i ripped out the focusing screen from my pentax super program and even though dimensionally it was about 1% smaller in width and height i put it successfully into my pentax mz-s, although the first time i put it upside down since there is no tab to guide me.

in the viewfinder you can even see a cut corner and i'm quite certain that alignment is off...

however focus is bang on, and so is the exposure.

so.. i dont know, just wanted to throw that out there..

[WerTicus]

yeah i had no trouble with my k20d it was easier than expected... it just fell into place and i closed it and it was perfect and i thought wow that was it