Re: [ATM] Aluminum mirror?

[GARY FUCHS <gary@rcn.com>]

Vladimir,

Thank you for your informative and insightful comments.

Cheers,

Gary Fuchs


>
>>A few days ago I found a telescope stuff vendor that offers blanks and kits 
>>for making
>>aluminum mirrors. Is there anyone in the group with experience with this 
>>material? How
> >about thermal distortion?
>
>I have no experience with aluminum mirrors but nevertheless this might help.
>Thermal distortion apart from expansion or contraction is consequence of
>temperature gradients in  material. Glass, being pure thermal conductor is 
>prone to such
>distortions. Therefore those rare ATMs that  use their scopes for observing
>are patiently waiting in the evenings for mirror to achieve thermal 
>equilibrium.
>Aluminum mirrors will  be better due to its  higher thermal conductivity
>which will bring them to thermal equilibrium (absence of thermal gradients) 
>more quickly.
>Thermal conductivity of aluminum is 200 times greater than same for glass.
>So much about thermal distortion.
>For one other possible distortion, aluminum mirror has also great advantage 
>over glass
>mirror. This is mechanical distortion, which happens when  mirror moves 
>under
> influence of  universal gravity and in the process hits the ground. More 
>often than not
> resulting mechanical distortion  is recognized as destruction (of glass and 
>self-confidence).
>This is very stressful but has nothing to do with the internal stress in the 
>glass unless
> the glass was tampered. In this particular case it is better if this 
>happens sooner than later.
>
>
>Regards
>Vladimir.
>
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