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Path: utzoo!utcsri!greg
From: greg@utcsri.UUCP (Gregory Smith)
Newsgroups: net.rec.photo
Subject: Re: Using lenses in cold weather?
Message-ID: <2229@utcsri.UUCP>
Date: Thu, 27-Feb-86 14:35:55 EST
Article-I.D.: utcsri.2229
Posted: Thu Feb 27 14:35:55 1986
Date-Received: Thu, 27-Feb-86 15:32:44 EST
References: <41600002@hpfcms.UUCP> <2208@utcsri.UUCP>
Reply-To: greg@utcsri.UUCP (Gregory Smith)
Organization: CSRI, University of Toronto
Lines: 26
Summary: 

[Not to be taken away]
In article <2208@utcsri.UUCP> hofbauer@utcsri.UUCP (John Hofbauer) writes:
>> What about lenses?  I've read that if I take a lense out in the cold,
>> I need to put it in a plastic baggie before bringing it back into the
>> warm house.  Is this true?  How cold is "cold"?  Any tips would be
>When you bring something into a warm environment from a cold one
>water will condense on it. Recall what happens to your eyeglasses.
>By placing it in a plastic bag and evacuating as much air as 
>possible will prevent the warm room air from coming into direct
>contact will the cold surfaces and so the condensation will occur
>on the outside of the bag. After a few hours the equipment will

Mostly true. When you bring a cold object in, water condenses on it. This
is because inside air has a higher _absolute_ humidity level than outside
air, and the object's temperature is below the dew point for the inside air
but not for the outside air. Sealing a lens in a baggie _before_ you bring
it in seals all that nice dry air in, preventing condensation. Note that
the _relative_ humidity is usually lower on the inside in the winter,
because heating air increases its capacity to contain moisture, thus
lowering the relative humidity even if the same amount of moisture is
maintained ( Relative humidity is (amount of moisture)/(max moisture) %,
where (max moisture) is the most moisture that can be carried without
condensation. This increases with temperature ).

Greg Smith
University of Toronto