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[OM] Re: Fungus

Subject: [OM] Re: Fungus
From: Garth Wood <garth@xxxxxxxxxxxxxxx>
Date: Thu, 31 May 2001 08:30:31 -0600
At 06:00 PM 5/31/2001 +1000, Oben Candemir wrote:
>I may as well ask these questions perhaps for the benefit of everyone:
>
>In my questions I'm assuming the ordinary amount of fungus... which is 
>typically spiderwebby and affects one or two lens elements.
>
>1. How significant a problem is fungus? ie. wil it affect any and all lenses 
>with time?

Ultimately, yes.  In practise, people who live in relatively dry climates (or 
who store their lenses and other glass in relatively dry conditions) may never 
see *significant* amounts of fungus on their optics.  The reason it's a 
potential problem for everyone is that fungal spores are everywhere, and can 
exist for millenia in a state of "potential" to establish fungal bloom.

Edmonton, Alberta, Canada (where I live) is a relatively dry climate.  I have a 
pro photographer friend who has never stored any of his glass in special 
conditions, and has no fungal problems with his optics to this day.  Some of 
his glass is over 25 years old.

On the other hand, I once stored some filters in my basement *without* humidity 
correction for about a decade, and found them coated with fungal bloom when I 
retrieved them.  The bloom came off with Windex and a good scrub with toilet 
paper, though I don't recommend this treatment for the faint of heart.  ;-)  
(Since Windex is ammonia-based, it *may* attack the metal coatings on coated 
optics; mind you, several of the filters that I cleaned were coated, and I 
noticed no problems [and still use the filters to this day]).

>2. How much does it really affect picture quality?

As the age-old answer goes, "It depends."  Is the fungus light or dark?  Does 
it cover a very small percentage of a single element's surface, most of one 
element's surface, or the surface of several elements?

>3. When cleaned how commonly does it reoccur? Sometimes, always, never, 
>depends on how you treat them?

See answer to "1" above.  Spores are everywhere, always.  Given the right 
conditions...

>4. Apart from the link on Siddiq's page on fungus.. is there any other links 
>or references to the fungus problem?

Probably.  Search Engines Are Your Friends.  (Hint hint).  ;-)

 *****

So, some summation (and opinion):

1. Fungal spores are omnipresent.  They're already in your glass.  Whether they 
ever "bloom" is a function of light, temperature and humidity.  Magic numbers 
for humidity are approx. 40% relative or higher.  Low light and cool (but above 
freezing) temperatures assist in this process.  Ultraviolet kills spores, but 
there's always more where they came from, and it's difficult to "bathe" the 
interior surfaces of the lens with high levels of UV for sufficient periods of 
time.  Also, "bathing" the lens with UV may cause damage to other (non-glass) 
parts of the lens in question.

2. Fungus, like any other intrusion into your optics, may or may not affect 
your picture quality.  The only way to know for sure is to have two samples of 
the same lens (one free of all detectable traces of fungal bloom) and compare 
two pictures from the two lenses under the same shooting conditions.  If in 
doubt, I'd assume that, at the very least, you'll lose some picture contrast (I 
have several photos where exactly this has happened, if anyone cares...).

3. It can be cleaned.  If the fungus has been there for a long time, it may 
have exuded a certain amount of acid to establish and anchor itself on the 
surface it's blooming on, which means damage to your glass and/or coatings.  
The only way to know for sure is to clean the lens and inspect it.

4. Humidity control, in my personal experience, is a *surefire* way to prevent 
spores from blooming (I had a Tokina AT-X 28-135 zoom which I stored in my 
basement, in a hermetically-sealed bag with dessicant, for over a decade, right 
alongside the above-mentioned filters, and it was pristine when I pulled it out 
and inspected it [Thank God]).  Some people have expressed unease with this 
method of control, fearing that dessicant will "dry out" the lens glues.  My 
opinion is that this is a false fear -- I'd be *extremely* surprised if lens 
glues were water-based or depended on certain humidity levels for their 
continued reliability, since that would invite instability in various places in 
the world where the humidity was either extremely high or extremely low.  I 
would've thought lens glues were one-part resins (possibly aliphatic, though I 
doubt it) which cured without water chemistry of any kind, but I don't know.  
It just doesn't seem reasonable to me.

My $0.02 worth.

Garth


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