Hi Paul,
Quote:
Originally Posted by Lismore Bloke
Thanks for the encouragement Les,
The closeness of the alignment stars (Achernar and Al Nair) probably contributed. Need more alignment stars for the Argo!
Cheers, Paul.
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Yep, the alignment stars may well be part of the problem. They are probably a little too close to each other and maybe too similar in altitude.
With a dob, from my personal experience, steer clear as far as possible from stars close to zenith (Dobsons hole) where the encoder tics are very, very closely spaced on the sky. Pick stars as far as reasonably possible apart and at significantly different altitudes. I personally don't use stars above 60 degrees elevation (as I suspect Al Nair might have been when you aligned) for aligning at all and try and aim to have one at about 30 degrees elevation and another at about 45 degrees elevation as far apart as possible. Might I suggest this month for early evening (about 8pm) Alpheratz (Alpha Andromedae) (bottom right in the Great Square of Pegasus when you face north) and Achernar (Alpha Eridani).
When you are doing a re-align on another object (as someone suggested) bear in mind where the last thing you aligned on was. For example, if you aligned on Achernar and then Alpheratz (in that order) when setting up, and then a half hour later decided to do a re-alignment on M15 while you were observing it. The alignment objects it then works on from that point are those last two (ie M15, Alpheratz) -- and they too close to each other for the alignment to be "well sampled".
Some people tend to go a bit overboard in the accuracy with which they align, using ultra high-power reticles etc to make sure it is exactly centred at x500. I don't think this is really needed if you take my advice above. I align usually using a 12mm or 9mm Nagler at x185 or x247 and just make sure the star as close as can be easily managed to centre of field and then hit the button.
Make sure your "Fix Alt Ref" step is done properly and that the two axis of movement are at right-angles to each other (or at the angle you have set anyway).
Also, make sure your "refraction" is on too.
I'm certain you won't regret this purchase -- excellent piece of kit! Best to run it off a small lead-acid 12V battery -- they are power hungry.
Best,
Les D