Mysterious Lens Issue. Fungus? Balsam Separation? Let's get to the bottom of this.

[ApMoore]

Hello hello!

Been lurking here for a long time but this is my first thread.

I recently acquired a 90mm Sekor C for my Mamiya RB67 which has an issue with the rear element. I had though it was fungus and went to work removing the rear element to investigate cleaning it out.

Unfortunately, the issue is between cemented glass so I'm unable to get to it but...

Is it fungus? I'm not so sure... I'm also not sue if it's balsm separation either...

Would anyone have any insights on this?

And of course if there's any ingenious solutions I might not have thought of.

Picture attached.

 

[Neil Grant]

...i think it's separation. Often a rainbow colouring is seen, maybe with the lens the other way around. Not sure you can do much about it - but the lens may still work OK.

 

[ApMoore]

...i think it's separation. Often a rainbow colouring is seen, maybe with the lens the other way around. Not sure you can do much about it - but the lens may still work OK.

So this is the thing. There's no rainbow here under any light that I can see.

I think you're correct though more likely to be seperation than anything else.

 

[Steve906]

Looks like separation, sometimes cleaning or other fluid can get in making it look clearer - no rainbow, or it's just too far separated for the rainbow effect.

 

[Nodda Duma]

Lens separation

 

[ApMoore]

Lens separation it is.

Looks like I'll be sending it back!

Thanks for chiming in!

 

[thuggins]

Fungus doesn't look anything like that. Are you certain it is a cemented pair? I've seen a lot of haze on lenses, but it is unlikely (though not impossible) that haze would show such a sharp edge.

 

[ic-racer]

I don't think it is balsam, therefore, it will be difficult to fully separate and re-glue. I'd look for a donor lens. Otherwise use it as is, or try separation and re-gluing, knowing it might be difficult. Some tips here, but there are many references out there:
https://www.outsidetheshot.com/balsam-separation/


I had a Topcor/Horseman lens with separation and I was able to find a donor lens (a Caltar brand which was identical) and replace the separated elements.

 

[eli griggs]

It may be fluid between separating lens elements.

Just a few months ago, my V.A. eyeglasses, had separation between elements in the right lens, which I onlyd after I had given the glasses a good wash with Dawn and water.

The interesting thing was, when the water was clean, after additional water without soap, I had a better vision in the center of those bifocals.

I have a large format Kodak lens that has balsm separation and the glue does no make the lens look any clearer where separation exist.

Putting the lens on a sunny window sill should cause any fluid to evaporate in a day or two.

It might also be possible to use the lens defect to draw thin balsm into the void using capillarity.

IMO.

 

[Nodda Duma]

That lens is too new to have balsam holding the elements together. Balsam separation looks different.
This lens uses UV adhesive to bond the elements together, which has failed and separated. This is what that looks like...a textbook case.

 

[eli griggs]

That lens is too new to have balsam holding the elements together. Balsam separation looks different.
This lens uses UV adhesive to bond the elements together, which has failed and separated. This is what that looks like...a textbook case.

Good to know, thank you.

 

[Grim Tuesday]

Bingo on the separation. UV hardened separation is less common, so people don't recognize it as well as they do balsam (and who knows, maybe it's also because the lenses that use it are newer, so it will get more common in the next 50 years). The only other lens I've seen have this style of separation is a Rodenstock Linhof Technikar in a Linhof 220.

Also OP, don't worry too much about performance, with this type of very minor separation the worst you are likely to see is a tiny decrease in contrast.

 

[ApMoore]

Thanks for chiming in everyone. Much appreciated and glad to get to the bottom of it!