>From: "Hans van Veluwen" <mail@xxxxxxxxxxxxxxxx>
>
>... The results are shocking! The SC lens weighs 367 gram, the MC
>version weighs 351 gram... Mind you, same lens!
>... the really shocking fact is that this
>lens is supposed to weigh, according to Olympus, printed both in the '79
>p-SIF and in the '85 Lens Handbook: 360 gram! So what's happening here?
I'm sure all list readers are familiar with "glass creep," in which glass
actually flows toward gravity over long periods. (If you measure some of
the oldest window glass, you'll find it is thicker at the bottom.)
What most people aren't aware of is that just as glass flows like water, it
also evaporates like water. I'll bet your MC lens has been out in the air
too long, while its heftier SC brother has been in an air-tight cabinet!
(When kept in a air-tight container, the glass vapor partial pressure
reaches equilibrium at "100 0lassidity," and further evaporation cannot
occur.)
So if you want to keep that precious Zuiko glass working well into the next
century, you'd better store it in a tight container! A little silica gel
wouldn't hurt, either, as it will evaporate first, raising the glassidity
to the point where your lens won't evaporate.
An interesting side-effect of glass creep is that if you consistently store
your lenses in one direction, either filter-end down, or mount-end down,
the glass creep will eventually change the focal length. (This is, in fact,
how aspherical elements are developed. "We'll serve no lens before its or
it's time!") So be sure to rotate your glass every few months, and you
won't suffer this problem problem!
(I am NOT going to explaint this 2,000 times. If you cannot simply accept
that I am right, then I'll have to just leave the list.)
(For the humor impaired ----> :-)
: Jan Steinman <mailto:jans@xxxxxxxxxxx>
: 19280 Rydman Court, West Linn, OR 97068-1331 USA
: +1.503.635.3229
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