At 08:34 PM 5/15/2002 -0600, Pete Prunskunas wrote:
>Maybe someone can explain this to me. I take great care of
>everything I buy, including lenses. I only own a few lenses -
>I am only a social Zuikoinker, not a raving Zuikoholic - but
>every one is crystal clear, with no fungus or dust inside. Maybe
>I'm lucky. But in many ebay ads, the description often states
>that there is "some" or "four or five speckles of" dust inside the
>lens. Just how normal is it? Is this a sign of unclean personal
>habits, or is it a case of "dust happens"?
Pete:
You're lucky. In virtually all lenses which are not internal-focusing, the
lens tube moves in and out while you're focusing. This in-and-out movement
either sucks air into the lens tube or blows it out. Either way, eventually,
dust will enter. It is impractical (and probably prohibitively expensive) to
completely seal lenses -- even the internal-focusing ones. Of all the lens
surfaces, keeping the rear external lens face clean is probably the most
important. The front external face comes a distant second (I have a
professional photographer buddy who never cleans the front elements of his
lenses), and the internal surfaces an even-more-distant third.
Garth
P.S.: Dust between the elements (as long as there isn't a large amount)
doesn't do anything to your photos -- the images of the dust can never resolve.
If there's a *lot* of dust, then you can see a decrease in contrast; if it's
light-coloured, an increase in flare (sometimes both together).
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