Quote:
Originally Posted by mick pinner
the majority of my goto's are now very good however it will not get close to Eta Carina Neb, 5-6 targets in a row will be spot on and then try Eta and it only just appears in the finder. what l did try was centering Eta and then going to M42, perfect, now go straight back to Eta and as l said just in the finders fov. any ideas?
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Hi Mick,
Thanks for the post.
Eta Carina the star or Eta Carina Nebula (aka NGC 3372)?
Keep in mind the nebula is extended and the center has a different
co-ordinate position to the star. Since the centers of many non-stellar
objects are determined by a weighted average, often from photographic survey plates,
and since the plates were sensitive at different wavelengths to that of the human
eye, what one may see visually through the telescope may not be
the complete picture compared to what was imaged photographically.
If you are after the star, use MODE CATALOG, BRIGHT STARS, CAR ETA
which is also the point many observers think of when they think of the nebula.
Now that you have established pointing, in some session in the near future,
you might want to perform a short Telescope Pointing Analysis System (TPAS)
run.
Here is a quick tutorial of how to perform a short run which acts as an
introduction to TPAS.
Stick to the GEM EXACT ALIGN setting.
Set MODE SETUP, SETUP MNT ERRORS, ACQUIRE DATA, SAMPLE MODE=ON.
Polar align the mount in your normal way (say to within a degree or better).
Align on one star.
DIAL up MODE CATALOG and the using ENTER, drill down through the
menu whereby the star you just aligned on will be the default
object that appear when you enter that menu. Eventually you will
see the GUIDE display appear. Press ENTER. The word
'DESCRIPTION' will be blinking. Spin the DIAL until it says
SAMPLE. Center the star you just aligned on and then press
ENTER to 'sample it'.
Now DIAL up MODE IDENTIFY, FIND STAR, FAINTEST MAG 3, IN ANY
CONSTEL, WITHIN 360 ARC and point to any other bright star in
the sky you are familiar with. Argo Navis should then display
its name in the top line and the bottom line will say 'FOUND'.
Hit ENTER and the GUIDE display will appear. Center the star in
the eyepiece. Hit ENTER to sample it.
Repeat the steps in the above paragraph for at least two other
stars (a total of at least four).
Go to MODE SETUP, SETUP MNT ERRORS, DEFINE MODEL.
Using the DIAL and ENTER button, set -
DEC INDEX ERROR ID=COMPUTE
HA INDEX ERROR IH=COMPUTE
POLAR LEFT-RIGHT MA=COMPUTE
POLAR VERTICAL ME=COMPUTE.
Make sure all other terms in the DEFINE MODEL sub-menu are set
to DON'T USE. Press EXIT.
In the SETUP MNT ERRORS submenu, dial up COMPUTE ERRORS and press
ENTER.
Argo Navis will scroll some information with regards the errors.
Hit ENTER at any time and successive times where it prompts you
with each of the four error terms above (ID, IH, MA & ME) and
accept them as USE NOW.
What you have done up to this point is computed and put in place
a simple model whereby the polar misalignment and what are
called the index error terms are the only terms within the
model.
If you want to get fancy, sample another star or two, or three
and in DEFINE MODEL set -
COLLIMATION ERR CH=COMPUTE
then once again, use the COMPUTE submenu and put the model 'IN USE'.
The above alone will probably make a dramatic improvement to your pointing!
To utilize the full power of TPAS, one needs to spend one evening performing
what we call a long sampling run. This entails sampling the position of
say anywhere between 40 to 100 stars across the sky. All this extra
data forms the ingredients for further analysis and may reveal other
pertinent systematic fabrication errors within your mount/OTA. TPAS then
allows you to save the value of any additional persistent error terms into
non-volatile memory. Then, on a subsequent observing run, you can re-sychronize
the model by sampling as few as two to five stars and you will then achieve
similar pointing performance as what you did on the night of the long sampling run.
TPAS is an advanced topic and is covered in the Argo Navis User's Manual in
the section on SETUP MNT ERRORS.
See
http://www.wildcard-innovations.com....mentation.html
for the User Manual online in PDF format.
The magic of TPAS is that it can cut through the tangled knot of geometric,
gravitational flexure and eccentric bearing errors within the mount and
take effects such as polar misalignment and refraction into account at the
same time.
Since your mount has the 4096 step encoders, as discussed on the telephone,
at some point in the future, you might consider upgrading them to the 10,000
steps effective solution. What the higher resolution encoders do is assist TPAS.
Since the significant pointing error residuals in many mounts result from
what would be seemily small mechanical errors within the mount,
such as tiny geometric angular offsets, the higher resolution encoders
help TPAS measure and characterize them with more certainty.
Best Regards
Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Phone +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au
Argo Navis Telescope Pointing Analysis System (TPAS)
