adjusting focussing screen on Pentax KM

[timo832000]

Since a couple of years I own an old full mechanical Pentax KM in pretty condition, only the focussing screen needs an adjustment to give a correct distance measurment.

How would you do this? Is there a standart method for adjusting focussing screens on analog cameras without having special tools?


best regards


Timo

[Gardener]

I am fairly certain that on Pentax K models you have to go through the top to access the focusing screen. Are you sure it is the screen?

[cooltouch]

Yeah, if you're having focusing issues, like for instance the distance scale on the lens isn't even close to where the lens is focusing when looking through the viewfinder. This could be caused by the mirror bumpers being worn out. It happened to my LX.

I own a KM, but honestly I don't know if it has interchangeable focusing screens. I would assume that it does not, since neither the K-1000 nor the KX has this feature. This means you have to remove the top of the camera and then the prism and other stuff just to get to the screen, which is permanently mounted in there. I don't see how a focusing screen would easily be moved out of position. But the mirror is exposed and more susceptible to being bumped around. Or the stops may have simply rotted away (like they did on my LX).

[timo832000]

What else could affect misfocussing?

[timo832000]

Ok, sounds logical....
So maybe I only have to replace those foam bumpers?


best regards


Timo

[cooltouch]

Yeah, probably so. But they aren't foam -- at least they aren't on my LX. They're little pieces of fairly hard rubber -- or some rubber-like substance.

[chhayanat]

[timo832000]

This is what it looks like, so aktually there is no rubber or foam. Just clean, black painted metal.




Timo
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[timo832000]

After a second inspection today my conclusion is, there is no bumper at all, just a fixed "hard stop". So what else could cause the problem?

By the way, the focus offset is not that big, It`s just a tiny little bit.


Thanks for your help

best regards

Timo

[Sciolist]

[timo832000]

Yes ofcourse, I have tried several lenses.
But logic already tells me that it`s about the camera because there is a diffrence between the focussing screen and the film plane.
I have already tried to mound a sheet of white paper in the film plane while camera back was open.
Difference was also clearly visible.

So what do you think what is wrong?

[Sciolist]

[timo832000]

New theory:

I believe it could be possible that the focussing screen is mounted in reversed position.
Maybe thats it. Does anyone have a KM or K1000 to tell me wether the rills are on the up- or the downside?

Best regards


Timo

[Gardener]

I am not sure what the rills are, but flat, matte side should face the mirror, and polished, convex side should face the prism.

[timo832000]

Everything else is excluded, another interesting thing is, that the camera looks like it has never been used, maybe it has never worked properly.

When I have enough time I will dismantle it, there is nothing to lose.


best regards,

Timo

[Gardener]

The repair manual for K1000 says that there are 3 set screws that control the position of the focusing screen and they are accessible from the front of the camera. I do not want to look for a KM in the Pentax pile but I have a K2 close by and indeed, there are two screws in the front corners of the screen and one in back, in the center. It looks like it might be a tedious process with a lot of trial and error, but it seems doable.

[timo832000]

Thx, I did not have that information yet!

[timo832000]

To give you an update: The camera is at Mr Stemmler (hopho.de) for repair now.
I am excited about what he is going to indentify as beeing the cause for the focussing problem.

[visualopsins]

It's fixed! http://forum.mflenses.com/pentax-km-smc-pentax-m-1-4-50-t79764.html

Please, what did he identify as the cause?