On Sat, 31 May 2003 23:47:03 GMT, Avogadro
<Avogadro@Acme.com> wrote:
>I bought a lens off eBay (35mm/2.0) and it arrived kind
of filthy, so
>I went through the usual cleanup of the barrel and
glass. This
>revealed the 30-year old specimen to be near-mint.
>
>Only thing is, there was still a film of some kind on
the front
>element. Several lens-cleaning tissues later, the film
was still
>there. Lens cleaning solution would not budge it.
>
>This film was not that bad, just enough to leave a sheen
on the lens,
>showing wipe marks. I found it annoying, though, so I
gingerly applied
>some isopropyl alcohol and wiped with the tissues. Made
no difference!
>
>What could form such a stubborn film?! What liquid do we
know that
>won't evaporate and is so persistent? Maybe silicone...
>
>I recalled that some lens cleaners for eye glasses are
made with
>silicone. Obviously not for use on camera lenses. But
who knows what
>this lens has experienced.
>
>I knew that silicone dissolves quite nicely in
hydrocarbon solvents.
>So with great trepidation, I wiped the element with a
tissue wet with
>paint thinner... let it evaporate completely... then
followed with a
>breath and another tissue. What a difference. No trace
of the film was
>left.
>
>Just thought I'd relate this... maybe someone else has
observed a
>stubborn film like this, or possibly has even caused it
by using the
>wrong lens cleaner.
>
>For clarification, the paint thinner was a low odor
hydrocarbon type,
>NOT lacquer thinner. Be careful - if you try this on
your gear, you do
>so at your own risk!
>
>Avogadro
Surprisingly, I've seen lens tissue (Olympus brand)
with silicone in it, and also "lens cleaners" with
it. It should be avoided, since good as the lens
looks soon after "cleaning", soon it doesn't look
so good, and the stuff is difficult to remove...