From: "Tom Krajci" 
To: 
Reply-To: "Tom Krajci" 


>From: "Mel Bartels" 

>The design that Roy Tucker developed is very workable.  He uses three
tubes
>within tubes that have metals of different expansions so as to get the
end
>points to never change position over the range of temperatures.  A
little
>heavy and cumbersome for ultralights so I've never built it myself, but
>quite doable for a permanent scope.  He basically never refocuses going
>many nights unattended.

>See http://gpobs.home.mindspring.com/gpobs.htm for more.

What about for a scope that slews to different parts of the sky?  Does an
athermal OTA typically suffer from 'slew-induced focus shift?'  Does an
athermal OTA that is immune to 'slew-induced focus shift' cost too much, or
end up being too difficult to fabricate?

Tom Krajci
Tashkent, Uzbekistan


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