Re: [ATM] undercorrecting?

["tony gondola" <acgna@comcast.net>]

I was under the impression that this myth had been busted a long time ago. 
Seems to me that there are simply too many variables involved here, 
thickness, mass, material, mounting, OTA design and orientation, speed of 
temp shift and in which direction. If the shifts are as large as the numbers 
you're showing then the effect should be easy to see and document via the 
star test.

Tony

----- Original Message ----- 
From: "J H M Gastel" <jhm.vangastel@wanadoo.nl>
To: <atm@atmlist.net>
Sent: Thursday, August 03, 2006 5:50 AM
Subject: Re: [ATM] undercorrecting?


>I read part of his articles and read hat the difference in Strehl ratio for 
>a slightly undercorrected mirror, warmed 2 degrees Celcius at the back 
>side, goes from 0.66 to 0.99. The Strehl of another, cooled mirror, went 
>from 0.51 to 0.79 after the same warming-up at the back side. He also says, 
>that the radiation gives a 2 degrees C difference in temperature between 
>front and back side of the mirror, so, according to Rohr, the effect is 
>large. I don't know of any other research pointing in the same direction. 
>Anyone else maybe? Or maybe evidence that it's not true?
>
>
>
>
>
>> Datum: 03/08/06 11:55 AM
>> Van: "laurence vincent"
>> Aan: atm@atmlist.net
>> CC:
>> Onderwerp : Re: [ATM] undercorrecting?
>>
>> hello
>> I already heard this assertion on behalf of proffessionel, to check it is
>> more difficult.
>> Look the work of Mr Wolfgang Rohr
>> http://www.astro-foren.de/showthread.php?t=6454
>> http://rohr.aiax.de/strehl-verb.htm
>> Franck grière
>> www.mirro-sphere.com
>>
>> ----- Original Message ----- 
>> From: "J H M Gastel"
>> To:
>> Sent: Thursday, August 03, 2006 8:57 AM
>> Subject: [ATM] undercorrecting?
>>
>>
>> > Sometimes the topic of deliberately undercorrecting large mirrors comes
>> up. On a Dutch mailinglist someone writes undercorrecting is necessary,
>> because a mirror, even a mirror cooled with fans, will never reach
>> equilibrium because of radiation of heat from the alumiumized surface of 
>> the
>> mirror into the kosmos. Reason why the face of the mirror will always be
>> cooler then the back side, which will deform the mirror. Maybe there is 
>> some
>> radiation, but I can't imagine that, in the case of a well cooled mirror
>> (well placed fans of sufficient capacity) the effect is so large that it 
>> is
>> necessary to leave a large mirror undercorrected. Did I miss something?
>> > Jan van Gastel
>> > http://home.wanadoo.nl/jhm.vangastel/Astronomy/
>> > _______________________________________________
>> > ATM mailing list http://www.atmlist.net/
>> >
>>
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>>
>>
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