Archived posting to the Leica Users Group, 1997/09/24

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Subject: Re: Filters
From: Eric Welch <ewelch@ponyexpress.net>
Date: Wed, 24 Sep 1997 22:34:33 -0500

At 09:52 PM 9/23/97 -0700, you wrote:
>Probably true on old soft coated lenses. I do not believe modern lenses are
>soft enough to worry about. Just be somewhat careful. How do you know when
>you have cleaned away the filter's coating? You could be, without knowing
>it, shooting through uncoated glass.

Actually, some high diffraction, low and anomalous dispersion glass is very
soft. Optical glass for the most part is pretty soft, but those are
especially. (Some of them). And they can be scratched very easily. One must
be extremely careful not to ruin the front element's coating, because once
it is, not only is the dollar value much less (no biggie for most users)
but the performance degrades. 

Leica in some books or brochures has said that obsessive cleaning has more
detrimental effect than the slight accumulation of dust on a lens. 

=============
Eric Welch
St. Joseph, MO

Maintenance-free: When it breaks, it can't be fixed