At 10:25 PM 01/11/2001 -0800, you wrote:
So how do dust get into the (older) lens? I can see fungus growing due to
moisture content, but dust? Or may be they are paint and whatnot from the
interior of the lens?
Lenses are open tubes, generally (this allows them to change their length
in focusing operations). As you move the tube back and forth during
focusing, air gets sucked in or blown out, and with it, dust. The only
exception to this are "internal focusing" lenses, which still have moving
tubes, but are enclosed in an outer tube of fixed length (so it can be
'completely' sealed). Even with sealed tubes, there are still mechanical
linkages which allow small quantities of dust in over long periods of time.
The dust is generally harmless, although large quantities of it can lower
contrast significantly. The dust particles do not resolve in the image.
Garth
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