Hi,
More thoughts about fungus.
This time only the spider-webby kinds, (not the yellow - green blobs in the
"middle" of the lens).
After you notice the fungus spreading over the optical surfaces of your
precious glass, where it will eventually affect image quality, what else is
there to notice?
What I've seen is that all infections start from the periphery. Now; why would
that be, I wonder?.
At the edge of the lens, it is mounted in the (metal) lens holder. There,
almost certainly, is an annular cavity. A ring-shaped cave of minute
proportions. Nice and cozy.
What I think happens is this.
A fungus spore gets inside the whole lens. That's not difficult, considering
that spores are TINY and everywhere. Every time you focus the lens, unless
it's an IF (internal focussing mechanism) lens like some Nikon lenses that
John Shaw writes about, air gets sucked in or expelled from the internal lens
cavities. And whatever is in the air comes along for the ride.
Sometimes water droplets must form inside the lens. Or, if the lens gets wet;
no problem; lots of water. Some of this will pick up fungal spores. What will
happen to the water? Some of it will get to the edge of the lens and then,
hey presto, capillary action will suck it into the annular cave VERY quickly.
Spores too.
So, what have we got now?
A moist little cavity that WILL NOT dry out easily because there is minimal
exposure to the outside air - even to the air void within the whole lens
system. The entrances to the little cave are truly minute. And a spore in the
cavity.
So, given this moisture and a little food, the fungal spore will germinate in
the
cavity. And grow. Eventually, sheer population pressure will lead it to find
the
few ways out, and start wandering over the surface of the glass where it can
pick up more moisture and food, and transport that nutrition back along the
hyphae to the home-base.
What next? A camera owner peers through the lens and spots the
wandering threads. OUT OUT damned spot! Off to a CLA with you.
And so the glass surface gets the treatment and swabbed and rubbed.
Return to the relieved camera owner.
All is well. Or is it?
Did the CLA give extra treatment to the source of the infection? Was the
glass-mount ring given treatment too?
I suggest that the ring (what ever it is called) that holds the glass element,
AND the edge of the glass element itself, are the very important places to
clean and disinfect, after the optical surfaces have been attended to.
Probably the most important, because the oldest hyphae are there, and
attached the firmest - to the rough edge of the glass and the metal.
This annular cavity is the important place within which to put fungicides,
because that's where spore germination will probably take place, and that's
where re-growth will originate from.
What do you think?
What do those on the list who repair cameras and lenses think?
My 2 cents worth, to copy another list-member.
Brian
----------------------------------------------------------
Brian Swale e-mail bj@xxxxxxxxxxxxxxx
140 Panorama Road URL = http://www.caverock.net.nz/~bj/fern
Christchurch 8008
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