Yellow patches

[ruben]

Can you explain how the yellowish color or the yellow patch is formed?

Is it possible to have a home proceeding designed for the cheapos, I mean taking into account the risk, to renew or strengthen the yellow patches in our old cameras ? It could be fantastic.

BTW, I know the pirat viewfinder proceeding of Rick Oleson, it is something, no doutbt, yet not enough.

Thanks,
Ruben

 

[Pherdinand]

it's a matter of coating the component that reflects the light into the vf. The problem is, those coatings are extremely thin, mostly metallic(i think) layers of a few nanometers only. A gold coating of 15 nm is already completely opaque.

You need to find someone working in thin film technology who can do it for you... 😀

 

[Pherdinand]

Now that you've reminded me...maybe i'll try to do it one day. We waste lots of resources here in the lab anyway😀

 

[Ash]

wow. if someone could manage to revive those patches, then a helluva lot of old camera's could be restored.

I'm sure theres money in it for someone who could work out a cheap process

 

[P C Headland]

On some cameras it is fairly easy to replace the half-silvered mirror in the RF. There are several places around that sell the half-silvered mirror (astronomy and optical supplies, surplus stores, etc). The other option is to grab the mirror out of a similar but dead camera.

I bought a couple of small sheets (one gold, one blue, cost less the US$5) and cut a new RF mirror for my Agifold camera (uncoupled 6x6 RF), since the old one gave a very patchy patch. The difficulty I would imagine is in re-adjusting coupled RFs so that they are accurate again, especially if the new RF mirror is of a slightly different dimension.

 

[Pherdinand]

I don't have any rf's that require this assistance, but if someone is ready to send me the piece of glass that has the fading/damaged/... rf patch from a whatever rangefinder, I would be prepared to try recoating it. No experience, no guarantee, so don't take your Leica apart yet!

 

[Ash]

I'm currently using the sticky-tape method.

Althought I could see the vague second image, it was really difficult to focus.

I followed the little instructions on someone's RF website to cut out a square of tape and place it over the front of the VF, so that the patch is more visible.


Any more details you can give on replacing the mirror bit?

 

[P C Headland]

Any more details you can give on replacing the mirror bit?

In my camera's case, it was pretty easy, as everything was very easy to access.

I looked around for some half-silvered mirror the same thickness as the existing RF mirror. I can't remember exactly what the spec of the mirror was, whether it ws 50/50 or 75/25 (reflective/transmissive). I then removed the RF housing and the old RF mirror and cut a new piece the same size. I then reset the RF for infinity and then checked the intermediate distances.

 

[Ash]

I think I'll wait til I have a spare body to destroy, as I'm afraid I'll have a very damaged Zorki and no rangefinder to use otherwise!

Thanks for the links

 

[Ash]

Zorki-4k.

I'm unfamiliar with most of the workings of rangefinders, but the yellowy focus patch on mine is very faint (serial number says it was made in 1975 if that makes any difference)

 

[Ash]

ah fair enough. any idea how to make the focusing any clearer? Aside from sticky tape?

 

[Ash]

I'm a little afraid of knocking the whole camera out of sync. Everything else is fine, and I'm not confident in myself enough to butcher the cam just yet