Quote:
Originally Posted by naskies
Roger - You've taken some beautiful photos! The laser polar alignment approach is ingenious - I can often see the SCP by visually star hopping between Crux, LMC, SMC, and the Octans, but lining it up through the polar scope is a challenging to say the least. The laser would make it very quick and easy.
Peter - Astrotrac claims a peak-to-peak periodic error of <= 5 arc seconds. From what I've read by people who have actually tested it, this is accurate. I'd say that poor polar alignment and tripod/ballhead flexure would be the usual culprit behind trailed stars.
I've used a guide scope with the AT - very good for drift aligning, and PHD works just like with my EQ6 except it doesn't have Dec guiding obviously.
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Thanks.
Interesting to hear of someone who's done autoguiding with it, I haven't tried that myself.
FYI, PE seems to not present its self in my images, but I haven't measured it myself.
Quote:
Originally Posted by barx1963
Hi Roger
Well done on using the Astro Trac so successfully. The laser idea was one idea I had thought of when I have been considering the AT as a possibility. The issue I saw with this was how to ensure that the laser itself is accurate, so the bean is actually pointing exactly parallel to the barrell of the laser and how to mount it accurately on the AT itself.
Malcolm
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I have two theories and I think either works fine, or at least seem to for me in practice. I used the first initially but then realised the potential of the second and use that more now but can't say I've had a problem with polar alignment being off either way.
1) I always have the laser rotated the same way, positioned on the same side/place of the AT. I hence very quickly become familiar with where the laser should be pointing near sigma oct for a good alignment, so any misalignment of laser or holder end up being factored in by just knowing where it should be pointing.
2) By putting the laser in and swivelling the polar alignment arm of the AT around the mount you see the extremes of pointing error in the configuration. So, looking through the binoculars you swivel the polar alignment arm around from side to side a couple of times quickly and the centre of the circle that is drawn in the sky by the end of the laser is where the true centre of alignment is and where you need to put the south celestial pole.
Not sure if they're scientifically accurate, but they seem to work
Roger.