[ATM] is mirror thermal equilibrium important

[James Lerch]

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

> Quite correct - but the dew hits the secondary first, does it not?

Indeed it used to prior to the dew heater upgrade.

> That one
> *is* small enough to radiate into the sky efficiently enough to dew up 
> (through
> the primary acting as a mirror). And fans may not make any air flow around it

I have a 2" fan blowing directly across each secondary, and it has a LOT of air
flow, but it still dewed over.  Here's a picture:
http://lerch.no-ip.com/atm/UpperFan.jpg

Prior to this years dew heater upgrade, dew would form first on the secondary,
then by midnight it would be forming on the primaries.  I have plenty of ambient
air flow over each optic.  So much so a comment was made by a fellow observer
one night that "The wind keeps changing directions" :-)

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)

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