Re: [ATM] asymptote to ambient

["matt" <mariusrf@bellsouth.net>]

see
http://medusa.as.arizona.edu/lbtwww/tech/ua9502/ua5.htm

and go to paragraph 5.2.3 "Tracking ambient", which states:
"The rule of thumb is that a 1.0 ° C temperature difference will introduce
0.3 to 0.5 arcsec of image degradation"

also see fig 5:
http://medusa.as.arizona.edu/lbtwww/tech/ua9502/fig5.htm

which shows a graph for rms wavefront error vs. various parameters .

the whole page is very interesting with references and quantitative data .

best regards,
matt tudor


-----Original Message-----
From: Don Clement <clement.focuser@verizon.net>
To: atm@atmlist.net <atm@atmlist.net>
Date: Tuesday, February 08, 2005 10:50 AM
Subject: Re: [ATM] asymptote to ambient


>
>
>
>> I read in a recent review of dew heaters that a mirror can drop below
>> ambient by radiative cooling.  If this is also below the dew point, dew
>> forms.  So by considering only conduction with the air, the approach to
>> ambient is asymptotic.  But by adding in radiative cooling, it is
>reachable.
>
>Sounds like mirror temperatures can be all over the place. Above ambient -
>below ambient -  thermal gradients within the poor thermally conducting
>glass   How close to ambient does the mirror have to be to not effect
>seeing? If the air in front of the mirror is sufficiently homogenized, is a
>large deviation of mirror temperature from ambient moot with respect to
>seeing effects?
>
>Don Clement
>Running Springs, California
>
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>

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