[ATM] is mirror thermal equilibrium important

[James Lerch]

----- Original Message ----- 
From: "Alexis Cousein" <al at sgi.com>


> In these parts, that rarely happens, at least with a Dob pulling air
> (and unfortunately also dust ;) ) from close to the ground. If that
> air gets close to its dew point, it's usually by having been cooled by
> the ground, and it will have shed some of its humidity by dewing up
> the ground, not the scope's mirror :).

I know with confidence that if you come to Florida for a few days with only fans 
as your Dew Control system, Dew will shut you down by midnight.  Been there, 
Done that, Got the Dew Blaster to prove it :)

Both my Bino's (the 8s and the 16s) suffered from dew with about the same 
severity.  The 8" binos had a different design than the 16, with the 8s having a 
closed back (no mirror exposure to the ground), where the 16's are open framed 
with baffles.

 Here's a picture of the fan arrangement on the 16
http://lerch.no-ip.com/atm/WSP_05/Bino_2.jpg

Here's one for the old 8" binos (no dew heating system, only fans and dew 
blaster)
http://lerch.no-ip.com/atm/Scope.htm

Why does dew do what it does, I can't say, but here's a link to the historical 
weather for Gainesville Florida for one of the nights in question:
http://www.wunderground.com/history/airport/KGNV/2006/11/17/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA

Of interest is the 11:53 PM observation,
Temp          41F / 5C
Dew Point  39F / 3.9C
Humidity     93%
Pressure 30.04in / 1013.7hPa
Winds Calm

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
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