Re: [ATM] The Challange and the limit

["Tom and Beth" <tomandbeth@theriver.com>]

DHA352 wrote (in reference to mirrors being thinner than 1:6 ratio )

"...for permanent environment controlled settings I
just don't see the advantage. "

Very few of us live in an area where the temperature does not deviate
more than a degree or so (1) over the time that the telescope is in use. So
while you may be able to control the environment during the day, it is 
difficult
to achieve the same effect while the scope is in use. In general, as the 
diameter
(and therefore thickness) increases, there is a benefit to increasing the 
ratio from
1:6 into the 1:xx or higher independent of the reduced weight-> mobility 
aspect.

(1) Numerous articles have been published (Sky and Telescope has several)
which discuss the temperature profiles of glass as a function of thickness.
These articles also discuss that more than ~ one or two degree difference 
between the mirror front and the surrounding air set up a turbulent boundary 
layer immediately in front of the mirror.

Hope this helps

Tom
Tucson, AZ

Date: Sat, 12 Mar 2005 16:36:35 EST
From: DHA352@aol.com
Subject: Re: [ATM] The Challange and the limit
To: atm@atmlist.net
Message-ID: <126.58afc9c8.2f64bae3@aol.com>
Content-Type: text/plain; charset="US-ASCII"


In a message dated 3/11/2005 11:38:02 PM Eastern Standard Time,
jdbaterson@msn.com writes:

>I think this 1:6 business of diameter to thickness must be a relic of
foolishness, >since we know that it needs be possible to produce the 
self-standing
form that is >very thin and maintains itself.

Call me a newbee.  But, I think all of this depends on your goal.  For one
person portables - I agree.  But for permanent environment controlled 
settings I
just don't see the advantage.

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