Fungus on a non-coated lens: your thoughts, please.

[Lachlan 717]

I have found an old 8" Pentac f2.9 lens (old aero lens?) that has a dose of fungus.

It is a non-coated lens. My understanding is that fungal blooms' big danger is the hyphae ruining the coating(s).

So, my question is: What damage occurs to non-coated lenses when Fungi attacks?

[Dan Fromm]

The fungus etches the glass. The etched surface scatters light. Hence, more flare, lower contrast.

[steven_e007]

Hi,

I have a Dallmeyer lens of similar vintage and uncoated, which also had a fungus problem (Mines a Serrac)

There are several different types of fungus, some worse than others. The worse kinds will quite happily etch the glass itself - sometimes giving spidery streaks - sometimes giving a frosted effect. Alas, mine was the latter - the edge of the glass looked like it had been sand blasted. Fortunately it is only the very edge, so the lens isn't completely ruined - but it might be a bit soft at full aperture...!

Best thing is to thoroughly clean the lens and then asses the damage. If you are lucky there may be none. If there is any - nothing much you can do, but at least it shouldn't get any worse as long as you store the lens so the fungus growth doesn't return (clean, very dry, cool). I cleaned my lens by dismantling the elements and washing them with detergent, warm water and a cotton bud. I was careful not to soak the housing in case water was pulled inside by capillary action. I then dried them quickly and thoroughly with warm air before a conventional clean with cotton and solvent (to remove the drying marks). The lens looked much better afterwards, but alas the fungus had done a little permanent damage.

Other types of fungus attack include growths in the balsalm, which is a different problem altogether and very difficult to do anything about. Best you can do is get plenty of UV sunlight through the the lens.

[Steven Tribe]

I have never seen an example of fungus attack (with surface damage) on old glass (pre-schott/1889).
I have never seen an example of fungus attack (with damage) in old balsam. I have seen changes that looks like fungus growth - but these were apparently due to the changes in the balsam itself. There may be uncoated "modern" glass which gets etched by fungal attack - but, again, I have never seen it.

By contrast, I have seen lots of glass etching from fungal attack in post WW 2 coated objectives. Seems pretty logical - coatings contain fluorides which converted to fluoric acid by the clever fungus - and this acid is the "best" etcher of glass there is.

[steven_e007]

I have never seen an example of fungus attack (with surface damage) on old glass (pre-schott/1889).
I have never seen an example of fungus attack (with damage) in old balsam. I have seen changes that looks like fungus growth - but these were apparently due to the changes in the balsam itself. There may be uncoated "modern" glass which gets etched by fungal attack - but, again, I have never seen it.

By contrast, I have seen lots of glass etching from fungal attack in post WW 2 coated objectives. Seems pretty logical - coatings contain fluorides which converted to fluoric acid by the clever fungus - and this acid is the "best" etcher of glass there is.

I, too, have never seen a fungal attack on the very early lenses, with their flint and crown glass (Rapid Rectilinears and Petzvals and such). It may happen, but I've never seen it myself, even though I've cleaned up some lenses that were in a filthy state and stored in damp conditions for decades. I have seen it in some lenses from pre WWII, though. My damaged Serrac is probably circa 1920...

[Lachlan 717]

Thanks, all. I need to have a good look at the lens (friend of mine had a look at it and she says it has fungus). It's cheap enough to buy anyway ($40), so could be a good test/project lens.

[sun of sand]

i have an uncoated retina xenon with extensive damage on one group and it still takes good photos

maybe the earlier lenses dont get attacked as much because the lenses are simpler-more air space or whatever between groups
thats my guess and im correct

[Brian Stein]

maybe the earlier lenses dont get attacked as much because the lenses are simpler-more air space or whatever between groups
thats my guess and im correct Or the ones that got hit bad ended up in the trash sometime in the last 50-60-70+ years leaving only the survivors... (the Darwinian approach to antiques?):)

[Lachlan 717]

Or the ones that got hit bad ended up in the trash sometime in the last 50-60-70+ years leaving only the survivors... (the Darwinian approach to antiques?):)

I like that, Brian!

Turns out that I purchased the lens for about $30, got the Exit Mold and a couple of cotton buds out and got myself a good piece of glass!

No damage to the surfaces; guess no coating was the key.

[Steven Tribe]

"Or the ones that got hit bad ended up in the trash sometime in the last 50-60-70+ years"

I am sure there is no difference in the quality of glass between those that were thrown away and those that turn up on that site. No matter how pitted and corroded the brass is, the lenses are always perfect ( apart from mechanical damage and brown balsam ).

Some years ago, an ocassional contributor to these pages - with a gift for fables - and who delivered an set of lens cells to me in a bar in Copenhagen in person - and who has seen more lenses than I have had bottles of Carlsberg - said that "old glass doesn't get surface damage from fungus - it is coated lenses that do". My experience since has only confirmed this.

[steven_e007]

"Or the ones that got hit bad ended up in the trash sometime in the last 50-60-70+ years"

I am sure there is no difference in the quality of glass between those that were thrown away and those that turn up on that site. No matter how pitted and corroded the brass is, the lenses are always perfect ( apart from mechanical damage and brown balsam ).

Some years ago, an ocassional contributor to these pages - with a gift for fables - and who delivered an set of lens cells to me in a bar in Copenhagen in person - and who has seen more lenses than I have had bottles of Carlsberg - said that "old glass doesn't get surface damage from fungus - it is coated lenses that do". My experience since has only confirmed this.

I wholeheartedly agree that very early lenses seem to be almost fungus proof. I rescued a Ross Rapid Rectilinear from a shed with a leaky roof that could have been there for many decades.... It was absolutely filthy and the brass was green with verdigree. After I scraped this off the metal was very heavily pitted and corroded. But, after careful cleaning, the glass is completely unharmed.

I'm not sure about the difference being coated or not coated, though. I think it is certain types of the later anastigmatic glass that are vulnerable - whether coated or not. All of the lenses in my collection that have fungus problems (not many, actually) are uncoated. Coating may add an extra layer of potential trouble - but you certainly can get problems on an uncoated lens.

[Marko Trebusak]

Some years ago, an ocassional contributor to these pages - with a gift for fables - and who delivered an set of lens cells to me in a bar in Copenhagen in person - and who has seen more lenses than I have had bottles of Carlsberg - said that "old glass doesn't get surface damage from fungus - it is coated lenses that do". My experience since has only confirmed this.

OK, I have to disagree with your theory Steven. I got Cooke Series II from 1912-1914 period, that was etched severely by fungus. And this was non coated (obvious) air spaced objective! It probably sat somewhere in the basement of some freak who like to see how objectives deteriorate. He also helped the process by miss screwing the threads and he did some other unpleasant things to poor thing. I got it for 70 quid. A friend of mine cleaned the fungus off and polished the damaged lens and corrected the threads, I had to correct a few other bits and peaces, but it's in good working order again. And I like that objective a lot.

Cheers,
Marko

[Steven Tribe]

I am no oracle! But, there are a number of early "new glass" objectives which are made from glass which did not stand up well to air and moisture. This was well known at the time, too. A number of designs made sure that the doubtful glass was as protected from the atmosphere as possible. I would guess that 1 or more of the TT&H Cooke triplet is made of new glass. General atmospheric degradation of the surface will provide an excellent growth medium for fungii - but surface damage was probably there already!