Re: Feather tracks in lens coatings - any preventative?

Dear Kevin and other members,

There is an excellent way to check what the etching on the lens coating is
and how it relates to the fungus and the kind of coating by looking at the
"feather" pattern using a good SEM.

There is a frequent contributor to this group who has assured me he will
use his superb instrument to take a look, provided he is supplied with a
suitable sample.

Is there anybody in this group who has a piece of optical glass showing
the discussed pattern which could be looked at using an SEM? Needless
to say that this will be destructive testing, that is the sample will have
to
be taken apart und a small enough piece be obtained for the described
purpose.

If you have a sample and like to contribute it, please let us know.

GR.


"Richard J Kinch" <kinch@xxxxxxxxxxx> wrote in message
news:Xns9AC3250261C23someconundrum@xxxxxxxxxxxxxxxxx
Kevin Cunningham writes:

Richard, the kind of damage is not cleanable on either a camera lens
or a microscope. The stuff is permanent.

The fungus itself can be cleaned off. If it has etched the glass, then
the glass is gone and yes, the damage is permanent. But fungus often
grows without etching the glass, and cleaning is possible without
permanent damage. This much I know from personal experience. Why it
sometimes etches and sometimes does not, this I do not know, nor have I
seen scientifically explained. Maybe it is the species of fungus, the
humidity conditions, the type of food, temperature, how old the fungus
has grown, who knows? It would be nice to know.

As regards Florida, I have to stick up for my home and assert that
humidity is a problem everywhere, because 60 percent RH is the magic
threshold for fungal growth, and temperate climates are frequently above
that. Indeed, Florida indoors can be dryer than up north, since people
here inevitably have air conditioning. Northerners also have damp
basements where they store things like cameras and lenses, which we
don't have here. So except for desert climates, you're not immune or
even less susceptible.

Dessicants are not trustworthy, either. They all saturate sooner or
later short of storing in a hermetically sealed container. Dessicants
in a porous container are ineffective. And people believe containers
are vapor-tight when they are water-tight, when it just isn't the case.
Polyethylene film is vapor porous, for example.

.

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