From: Mark Holm 
To: dbates59{at}yahoo.com, atm{at}shore.net
Reply-To: Mark Holm 


Bob May wrote:


> Make sure that you have the autofocusing off
> for the program or it will refocus to get the best shape and that will be a
> problem in reality as the focus will then change as the attitude changes.
>


I can't agree with Bob here, at least not entirely.  If you will be using
the scope for visual observing, the focus shift isn't going to be a big
problem. You
will probably refocus or change eyepieces more frequently than would be required
by this phenomenon anyhow. Even for photographic and ccd work, I think too
much has been made of this focus shift due to Plop's refocusing.  The
numbers typically come out less than 0.05 mm.  How many telescopes have
tubes/trusses temperature compensated to produce less than 0.05 mm of
movement during a long exposure?  How many are stiff enough to prevent this
much movement during a long
exposure?

Mark Holm
mdholm{at}telerama.com

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