Photomic F TN finder. Fungus or de-silvering

[WILL WORK FOR FILM]

My new Nikon F TN is all cleaned up and being put through it's paces but there is a nagging issue that is concerning me. After carefully removing the handful of lint and debris from the focusing screen I have a clear viewfinder with the exception of what looks like either fungus or de-silvering. It is definitely inside the finder prism. Here is an image of what I am seeing.

 

[WILL WORK FOR FILM]

I can live with it as long as it is only de-silvering. But if it turns out that I have a fungus problem, need to take care of it and separate it from my other equipment. The picture is deceiving. The right side is the reflection of the left side in the prism. While looking through the viewfinder I see it at the bottom left. I have avoided fungusy equipment till this point and am not really sure what it looks like. Would expect it to be sort of a spider web pattern if it was fungus. It looks to me more like a powdery residue.

 

[WILL WORK FOR FILM]

In working on several F's I've seen a fair number of desilvering situations.

Does this look like a typical case of desilvering?

 

[flavio81]

My new Nikon F TN is all cleaned up and being put through it's paces but there is a nagging issue that is concerning me. After carefully removing the handful of lint and debris from the focusing screen I have a clear viewfinder with the exception of what looks like either fungus or de-silvering. It is definitely inside the finder prism. Here is an image of what I am seeing. View attachment 173383

There is fungus on the side that faces the focusing screen. This can't happen on the inside of the prism, because it is by definition a solid piece of glass.

As for desilvering, it is too common on Nikon F prisms. Just ignore the desilvering problem. I always wondered if Nikkormat prisms could be used as substitute!

 

[WILL WORK FOR FILM]

There is fungus on the side that faces the focusing screen. This can't happen on the inside of the prism, because it is by definition a solid piece of glass.

As for desilvering, it is too common on Nikon F prisms. Just ignore the desilvering problem. I always wondered if Nikkormat prisms could be used as substitute!

So if I am understanding , you are of the belief that it is desilvering and NOT fungus? I can live with the desilvering.

 

[WILL WORK FOR FILM]

I just found a tutorial online that explains how to disassemble the photomic heads. It explains that the foam spacers used would degrade and damage the prism over time. An image showing the rotten foam and the pattern it leaves matches the pattern in my viewfinder to some degree. I am now of the belief that it is in fact desilvering. I will just live with it. There is no way I will ever pay $300. + for a plain prism head. I don't think I will ever try to get the TN meter fixed either. I had every intention of using this camera completely manually to begin with. Just didn't like the idea of fungus spores in my equipment.

I do have another question in regards to the F's with the Photomic heads. As I have stated, I do not intend to use the meter. There will be no batteries in the camera. Most of my lenses, except Series E 100mm f2.8, have the rabbit ears to link to the metered head. So far I have coupled the rabbit ears and set the max aperature to the desired film speed. How does the lens communicate with the camera in a way that that max aperature/ISO setting matters? In other words, Does it really matter if I match up the aperature/ISO without a functioning meter? The Prism heads don't have the rabbit ear coupler. Do they have a different means of communicating ISO speed?

 

[flavio81]

No, a Nikkormat prism will not work at all. Completely different configuration.

Hi, many thanks for the reply. So it will not fit at all? Or will fit but without the meter PCB mounted on top?

I want to repair a desilvered photomic head and will be happy with it even if i remove the meter circuits.

 

[flavio81]

In other words, Does it really matter if I match up the aperature/ISO without a functioning meter?

No, it does not matter at all.

 

[flavio81]

No, a Nikkormat prism will not do. Once you open up both you would see why. Cannot be done no matter the intent.

Thanks APUGuser19, you have saved me valuable hours of time !!