Re: ATM another question

[Mel Bartels <mbartels@efn.org>]

UC007@aol.com wrote:

> IMHO the only way to rotate the focuser and maintain collimation short
> of a
> lot of very expensive machining of very expensive castings, is to
> rotate the
> whole telescope in its mounting saddle. This arrangement is non
> critical in
> so far as smoothness of bearings and concentricity is concerned. As
> long as
> the tube itself is stiff enough, the relationship between mirror,
> secondary
> and focuser remains unchanged.

On the other hand, I have used Dan Bakken's 41" f/3.9 with rotating
upper end, and it does indeed work, maintaining collimation (at f/3.9,
you would know if it didn't!).  His upper end is made with ordinary
tools.

--
Clear skies, Mel Bartels    Programmer/Analyst, amateur astronomer
Eugene, Oregon, USA         homepage: http://www.efn.org/~mbartels
mailto:mbartels@efn.org     atm, atm-digest list-owner
Motorize A Dob: http://zebu.uoregon.edu/~mbartels/altaz/altaz.html