So that's why I keep finding marbles in the bottom of my camera bag...
Jan Steinman wrote:
> >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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