Quote:
Originally Posted by ausastronomer
It is also worth mentioning if you are limited for time, you can do a short pointing run of about 5 stars, carefully selected, just use the Index Error (IE) term only and pointing accuracy will usually be improved to put everything into the FOV of a medium power eyepiece. Clearly, the larger the group of stars sampled the better the pointing accuracy attainable, but it is comforting to know that this shortcut offers a good improvement, if you don't have much time.
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Hi John,
Thanks for the post,
A little background as to what is going on here might be helpful.
As you know, the encoders used are incremental encoders and have no
zero reference point. As it turns out, one needs to establish the zero reference
point for at least the Alt encoder. This is the job of the FIX ALT REF step.
FIX ALT REF has a powerful feature called AUTO ADJUST, whereby after
performing a two-star alignment, the ALT REF point is automatically adjusted
based on the information obtained from aligning on those two stars.
When one uses TPAS and the mount type is set to ALT/AZ DOBSONIAN,
something interesting happens when at least four stars have been sampled
and the IE term is set to COMPUTE. The IE term is the Index error in Elevation
term and is analogous to what AUTO ADJUST would normally do. What happens
is that rather than adjusting the Alt encoder zero reference point based on
the position of just two stars, one is now using all four stars. As the number
of sampled stars increases, all can be used to contributing to the establishment
of the Alt encoder zero reference point. In other words, TPAS effectively
provides a "super auto adjust" function.
In practical terms, as you point out, sampling just a small number of stars,
say four or five and just fitting IE can make a dramatic improvement to the
pointing performance of some scopes.
Best Regards
Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au