From: "Mel Bartels" 
To: 
Reply-To: "Mel Bartels" 


>>>
What have you heard about athermal optical tube assemblies...do they
maintain focus tolerance as the scope is moved to new targets...or is the
concept of an athermal optical tube assembly more market hype than
practical use to the amateur with a finite budget?
<<<

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.

Mel Bartels

--- BBBS/NT v4.01 Flag-4