Shel Belinkoff writes:
> I don't know how accurate that is. It seems that a lens has to
> be vented in some manner to allow for air to move when
> temperatures change, or when element groups are moved when
> focusing.
I think the elements themselves are generally sealed pretty airtight until you
get to the aperture where mechanical couplings need to get in. This is
based on having cleaned out an SMCP 50mm f/1.4. IIRC, all the glass in
front of the aperture can be unscrewed as a unit; the same applies to all the
glass behind the aperture.
As you say there does need to be some kind of venting to allow the thing to
focus. When applying this to FREE lenses I get worried. With non-FREE
lenses, dust inside the body can be blown out or removed off the rear
element easily, but with these lenses dust could easily get onto the inside of
the rear element. When you consider the large extension of the FA100/2.8
macro, a lot of air is going to get sucked into that thing. Having said that,
mine isn't showing any problems yet.
Cheers,
- Dave
David A. Mann, B.E.
email [EMAIL PROTECTED] * http://www.digistar.com/~dmann/
"Why is it that if an adult behaves like a child they lock him up,
while children are allowed to run free on the streets?" -- Garfield
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