[APML]: Off axis Guiders

[charles@cjf.noli.com]

AS>A newbie question..... 

AS>What should I reasonably expect regarding guide star image quality using
AS>an off axis guider with a SCT (f/10 or reduced to f/6.3). My first
AS>impressions have been that the potential guide stars, are like looking at
AS>dim fuzzy stars through a poorly collimated scope. Is this inherent in the
AS>design of a OAG and a result of capturing only a small part of the light
AS>cone or is it a bad OAG. Help! 

Since the star images are picked-off by a small prism in the OGA they
have a distorted quality. It also depends on the quality of your IR
eyepiece. My humble advice is to start by picking photographic objects
that have a lot of bright guide stars in the vicinity, particularly
near the Milky Way. For instance, M11 is a much more richly populated
area than M13. Once you get the hang of guiding with relatively bright
guide-stars, the fainter ones seem less intimidating. It is also a
question of practice. There are little tricks to prevent the eyes from
getting fatigued, and having the guide star phase in and out of view as
a result. A pulse controller is a great gadget. Having the IR disappear
every three seconds gives the eye relief from glare, and allows one to
find a faint star that has faded from view. The big problem I have with
these guidestars is when only a faint double star is available for
guding. It is difficult sometimes to tell the components apart, and one
can easily get confused. Its quite comical actually.

Hopes this helps...

C.S.