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Old 25-09-2008, 12:59 AM
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gary is offline
Join Date: Apr 2005
Location: Mt. Kuring-Gai
Posts: 5,430
Originally Posted by ausastronomer View Post
I would be turning atmospheric refraction "off". If you are doing "normal" Deep Sky and Planetary observing it is not necessary to use it. Whilst it's a nice feature to have in some cases for certain specific purposes, it is not necessary in most normal observing situations. With refraction turned off and a good TPAS model established both my scopes point with an accuarcy better than 10' even very low down.
Hi John,

Thanks for the post.

You are absolutely correct in that most Dob owners could get by with REFRACTION
set to ON. As you are aware, refraction effects becoming larger as you near the
horizon and most Dob owners shun this part of the sky. However, we still recommend
to keep it ON as a matter of course and in particular when you perform a TPAS

As it turns out, the NPAE and CA terms are hard to distinguish unless you
take a reasonable number of samples spread over the sky but in particular
having a good spread in Altitude, from near the zenith down to the horizon.
As the effects of refraction can be extremely significant near the horizon, it
is important for the TPAS analysis that REFRACTION be switched to ON.

Best Regards

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