ATM Newt 20 parameters

[Carl Woebcke <carlw@telis.org>]

Thanks everyone, for your help in finding Newt 2.0,
Now that I've got it, I have a few questions:
I'm planning an 18" Dobs, and trying to determine the shortest safe
focal ratio that allows a 2.61" diagonal (to minimize contrast).  So
here's my questions:
1) What's the lowest-profile, decent, 2" focuser on the market for
strictly visual use?  The JMI NGF-2 has a height of 1.53", to which (if
I understood him correctly) Mel suggests that I add 1" to calculate to
the focal plane, but that the short height Novak helical focuser mounted
from the inside takes about 1" off the JMI distances (i.e., a TOTAL of
1.5" from the base of that focuser to its focal plane?).
2) In Newt2.0, can I therefore use 1.53" for "Focuser Height" for the
JMI NGF-2, but 0.53" for the short height Novak helical focuser mounted
from the inside?
3)  In Newt2.0, what should I put in for "Focuser Extra travel"?
4)  In Newt2.0, what does "Diagonal Offset" mean (still alluding me)?
5)  In Newt2.0, what does "Front Aperture Diameter" mean?

Thanks again(in advance) for everyone's help and for all your past help,

Carl Woebcke
carlw@telis.org