Re: ATM Composite Materials For ATMs

["Benoit Schillings" <benoit@be.com>]

>Having both a strong back and a limited budget, I'll take aluminum any 
day.
>Besides, when you're dealing with a 30 pound mirror, a counterweight, 
and a
>box filled with brass and aluminum eyepieces, a few ounces of metal 
won't


Hey, no problem if you prefere AL... I have no stock in Carbon fiber ;-
)

For me, Carbon fiber is nearly a must... 

On a 15 inch F/12 cassegrain, a change of temperature of 1 degres is 
enough to trow
my images out of focus if I use an AL truss tube... Carbon fiber rules 
for that
kind of application (unless you really want to use INVAR !).

(15 inch F/4 is about 50 inches long... AL CTE is 25 ppm... means for 1 
degres about
31 microns... with the amplication of the secondary (3x).. this means 
31 microns * (3*3)+3
= 370 microns !)....


I use a carbon pole for the main telescope structure and uses a short 
rod of Aluminum
going in the other direction for the secondary holder... that way I can 
nearly completely
athermalise the scope.


                -- Benoit