ATM focuser placement

["Cho, Wilson" <wcho@microsemi.com>]

Hello:

  Having followed the emails on the focuser placement,
and how critical the "xtra travel" has to be figured for 
eyepiece focusing, I have a question that maybe someone can answer.

  I am currently building a telescope and plan on using
a low profile focuser (a la the Crayford on the ATM
page). I have several eyepieces, but no Barlows at this time.  When I
finally get the Barlow (sometime AFTER I
get the scope finished), here's the question:

  How much "xtra in travel"
should I put into the measurement for 

1) a regular length Barlow; 
2) if I use a Shorty Barlow instead.
3) What are the advantages of the two types of Barlows?


  I don't dare to drill any holes or place the mirror
box until maybe the experts can possibly provide some
direction!

Keep this list goin'!  I have learned so much about
the nuances of ATM'ing, that no single book can replace!


wilson

wrcho@yahoo.com