Re: [Paddlewise] Waterproof Binoculars

M. Lenon wrote:
> 
> >Does anyone have a recommendation for waterproof binoculars?
> 
> Hi Chris,
> 
> Go to: http://www.gwi.net/sing/BVD.html
> 
> This is a wonderful site where I learned more about binoculars than had I
> gone to the library. 
[snip]
 
> Most, if not all, waterproof binocs are "nitrogen purged." This is somewhat
> ambiguous. What the lens barrels are actually "purged" of is normal air.
> They are then FILLED with nitrogen and sealed with O-rings. Nitrogen is an
> inert gas that cannot hold moisture, and does not react to temperature
> changes, thus maintaining an even pressure.  (In motorsports, Indy cars, for
> example, use nitrogen in their tires, rather than air. That way, hot or cold
> tire temperatures do not affect the inflation pressure because the nitrogen
> doesn't expand when the tires are running at their normal 200+ degrees
> operating temperature. Tire pressure greatly affects handling. Neat, huh?)
> Back to your binocs. Air holds moisture. Sudden temperature changes like
> bringing cold binocs into a warm room can cause condensation to form on the
> lens surfaces just like on a cold drink glass in hot, humid weather. 
[snip]

Hi, Bruce:

A couple of small corrections to an otherwise excellent treatise on
binocs:

1. Nitrogen can hold water vapor, and in the same concentration as any
other gas.  Air has no special property which allows it to hold more
water vapor.  I think the binocs manufacturers purge (then fill) binocs
with DRY nitrogen, which has had all moisture removed from it.  Then, as
long as the O-ring seal is not compromised, no moisture can enter the
binocs, and, voila!, no condensation on the inside.  Nitrogen is used as
the purge gas (most likely) because dry nitrogen is useful commercially
and is more available than dry air.

2. It's not true that nitrogen will not expand when heated (re: comment
about Indy sports cars).  The Ideal Gas Law applies equally to all gases
(and, mixtures of gases) at the sorts of pressures and temperatures in
tires.  I am puzzled, nonetheless, why they would bother to inflate with
nitrogen, unless they are concerned about oxygen-stimulated degradation
of the tire rubber.  That seems unlikely, given the short lifetime of
Indy rubber.

Thanks for an otherwise informative and authoritative treatise on
binocs.  (I just invested in a waterproof pair of Canon binocs, after
many years of avoiding a dunking for my Nikon TravelLites.)

-- 
Dave Kruger
Astoria, OR
sea kayaker -- and chemist
***************************************************************************
PaddleWise Paddling Mailing List
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.gasp-seakayak.net/paddlewise/
***************************************************************************