Fungus or Separation????

[dap]

Hi all,

I need some opinions on a lens that I have. I have a lens with a flaw in the glass but I can't quite peg what the problem is. The pattern is definitely located between a cemented pair (not on the lens surface).

All of the fungus I have seen before showed up as dense branching blobs - these seem more sparse.

All the cases of separation I have seen have been that obvious amber ring around the element or that diffuse rainbow sheen around the edge.

It almost looks like glue between the edge of the elements on this lens has fractured. Under the right type of lighting it looks like rainbow colored branches.

What do you think?

If it is fungus I might try to separate the cemented pair and clean/re-cement. If it is separation I'll just leave it.

Thanks

PS - that visible ring around the edge of the glass that looks like separation is just accumulated dirt/grime

[redu]

If you are sure that this fault is between two cemented elements does it really matter what it is? I see two options here

1) You have to have it separated and recemented (alternatively you may try to do it yourself by relying on the information you can easily find in this forum)
2) Use the lens as it is since i think it will disappear with a slightly smaller aperture than open.

Looks to me like funghi though.

[Dominique Cesari]

Fungus

[Dan Fromm]

Fungus. Separation usually manifests as Newton's rings.

[Steven Tribe]

Is this a post WWII lens?

[dap]

Is this a post WWII lens?

Pre-WWII

[IanG]

Looks like Balsam separation.

Ian

[Steven Tribe]

I thought it might be fracture associated with the early "dodgy" synthetic cements.
Note that the paths end at similar distance from the lens edge on one side.
100% sure this is Balsam "something or other". There may be fungus spores in the paths but the cause is a balsam fault.
"Rainbow coloured" sounds like typical newtons rings from microscopic air gaps. This might be a suitable candidate for the recent discussed heat treatment?

[J. Fada]

It looks like separation to me. If this is the case, put a small drop of thin oil on it and let it wick into the gap overnight. In the morning I doubt whether you will even be able to find where the marks were. I have done this in the past. It is an easy fix instead of recementing. I have done that in the past too. Go the oil route first.

[Geoffrey_5995]

If the damage is on the surface of the glass, take a loupe and see if the imperfections are etched into the glass, it would look like engraved channels. This would indicate fungus. If the imperfection is in between the two glasses, most likely separation. I have taken apart and re-cemented many lenses that I was certain was fungus between the glasses and it turned out to be separation. Separation takes many forms, Newton rings, paisley like flowers, crystallization, crackling like a dried desert after a rain so it is easy to think it is fungus because the patterns can be quite interesting, organic looking and beautiful. But separation does not leave etching in the glass, fungus does and this etching would be a tell tale sign that I have only seen on an air spaced surface. I guess it could also appear in a cemented surface but unlikely. From what I remember, UV light kills fungus so it can be left in the sun to kill the fungus, if it isn't dead already. Hope this helps