Quote:
Originally Posted by h0ughy
Gary,
say the argo is fitted, lets say you are out by heaps in finding the SCP, could you use the AN to precisely find the SCP instead of drift aligning?
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Hi h0ughy,
Thanks for the question.
Indeed, Argo Navis can do precisely that.
If you had no idea where to find the SCP whatsoever, there is one procedure
using the ALIGN function alone that will assist you in homing in it.
Once you are within a couple of degress, you can then use the polar alignment
feature of TPAS to further refine the polar alignment,
For example, if you are like me, you simply go outside, naked eyeball the
Cross and the Pointers and plonk the scope down. I can usually plonk the
mount down within a couple of degrees of the SCP. I will then perform
a one-star alignment and sample the position of anywhere between four
to six stars. The system will then report to me the amount of polar misalignment
in azimuth and elevation for the mount. What I then do is tell TPAS
to switch off the polar misalignment errors and I then GUIDE to a star.
The star will not be centered. I then adjust the mount in azimuth and elevation
until the star is centered. I am then polar-aligned.
The problem with a drift test is that it does not take into account the
geometric, gravitational flexure and any eccentric bearing errors within the
mount/OTA. These 'mount fabrication errors', along with polar misalignment
errors are entangled in a very complex way. What TPAS can do is magically
untangle all these errors for you. Most importantly of all, it then reports to
you its results in statistical terms. I cannot over empasize how important
a feature that is in any mount error and analysis correction system.
This statistical information can provide you with degrees of confidence in
the reported results. Without it, you could never be really sure whether
that the reported corrections are to be believed or not.
By way of further background, to use TPAS to its fullest, typically one
devotes one night to performing a long pointing test. For a mount like
a G-11, you might devote one Full Moon night to sampling perhaps 50 to 100
stars. TPAS will then provide statistical information on the mount's pointing
performance as well as what error terms contribute significantly to the
pointing model. Based on the information TPAS provides, you may even choose
to make mechanical corrections to the mount itself. For example, if it reported that
the OTA was not orthogonal to the Dec axis, you might decide to shim the OTA.
(If you don't, there will be a region around the pole your scope will not
be able to point). Alternatively, you may decide to not mechanically adjust
anything and simply let TPAS provide a pointing correction. The system allows
you to save a model from a long pointing run for use on a subsequent night.
When you take the mount out again on a subsequent night, you then typically
peform a short pointing run of perhaps four to six stars. This allows you
to re-synchronize the model and to re-determine the polar misalignment
terms.
Large professional observatories using nearly identical analysis techniques
as discussed above to improve the pointing performance of their scopes.
Like most users, I find TPAS faster and more convenient than a drift test
as well. There is no need to own a polar-alignment scope nor any
requirement to find Sigma Octanis.
You can read more about TPAS on pp 115-142 of the Argo Navis User's
Manual. See
http://www.wildcard-innovations.com....n/argoman8.pdf
Remember, if you ever see a system that claims to provide mount error
correction or polar correction but
does not provide statistical feedback,
treat the results with scepticism. There are many reasons for this, but
one of the most important attributes of a model is its predictive behaviour.
For example, it is one thing to have a pointing model that provides
corrections for the mount on one night. However, ideally the model should
be able to provide corrections for subsequent observing sessions in the future.
Only with statistical results can one have any level of confidence in a model's
worth at some point in the future.
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
![[1ponders]'s Avatar](../vbiis/customavatars/avatar45_9.gif){kind=avatar}
doesn't make sense to me. 
. I have yet to read the manual on anything and I have just sent away for the upgrade to version 4 for the gemini
