Beginner question about Polar alignment

[Fenris]

I just bought a SW star adventurer and FINALLY there's mostly clear skies, so i wanted to try it out between the fogspells. The Polar scope has a dial with marks that looks like a clock. I have the polar Align app so i know where Polaris is supposed to be, so i got it as close as i could. My question is this: when i now have turned it on celestial tracking, if the alignment is good, then Polaris should just follow the dial around the "clock" right? And how long do i have to wait before i can see if it's good to go for AP? Is this what you call drift alignment?

[Tinker1947]

If you have polaris position correctly, turning the SA on its axis Polaris should stay on the circle for a full turn, depending on the kit you are mounting on the SA a DSLR plus Lens should give you 5 minute images with no star trails, if you do get star trails look at the balance this needs to be very good.......

[Juel]

Yes with good polar alignment, Polaris shouild stay on the circle as the mount tracks. However, it would make one full turn in 24 hours, so looking through the polarfinder to see if alignment is good is impractical at best. Instead, once you think you have a good alignment, take a test shot with your camera. Zoom in on the photo and look for star trails and thus decide if your aligment is acceptable. This is done easiest with a shot of the sky towards the horizon, as the movement of the stars are more pronounced there.

[glowjet]

All you have done is carried out a first basic Polar alignment, drift aligning is something totally different. I suggest you Google drift aligning and have a look at the many tutorials on the subject, enjoy the forum

[Astrosurf]

Have a look here for drift alignment:

http://www.cloudynights.com/page/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760

I agree with what's been said. Ensure your altitude is as accurate as possible with the altitude dial. I make sure my mount is level too, so it's not dipping forward or back. I then get Polaris at its current position on the larger circle using Polarfinder, as you said, and ignoring the little circle. Then I rotate the mount's RA to check Polaris isn't drifting off the circle (obviously with no telescope mounted!) then attach the kit and balance. Oh, and quickly check again that the weight change hasn't moved Polaris off the circle. I use terracotta plant pot saucers under the tripod feet to stop them sinking into grass. My hubby drilled a depression in the centre of each so the feet don't slide. Good luck!

Alexxx

[Fenris]

Good idea about the pot saucers!

When i get Polaris on the circle there it's supposed to be, could i also check alignment by rotating 180-360 degrees? If i have good alignment then the star should stay on circle while i turn right? Or maybe that would be completely wrong since Polaris is supposed to be the one to move... Haven't finished the book Deep sky imaging Primer yet, so probably a couple of stupid questions

[Astrosurf]

Good idea about the pot saucers!

When i get Polaris on the circle there it's supposed to be, could i also check alignment by rotating 180-360 degrees? If i have good alignment then the star should stay on circle while i turn right? Or maybe that would be completely wrong since Polaris is supposed to be the one to move... Haven't finished the book Deep sky imaging Primer yet, so probably a couple of stupid questions

Yep, as I said, rotate the right ascension part of the mount and see if Polaris drifts off its circle. It has to stay on its circle as that shows its 24hr motion.

[gnomus]

I just bought a SW star adventurer and FINALLY there's mostly clear skies, so i wanted to try it out between the fogspells. The Polar scope has a dial with marks that looks like a clock. I have the polar Align app so i know where Polaris is supposed to be, so i got it as close as i could. My question is this: when i now have turned it on celestial tracking, if the alignment is good, then Polaris should just follow the dial around the "clock" right? And how long do i have to wait before i can see if it's good to go for AP? Is this what you call drift alignment?

You might also want to consider the inherent error and tolerances in polar scopes (that are a relatively cheap piece of kit).  I'd use the polar scope exactly as you have been doing to get 'roughly' polar aligned.  I wouldn't try to set polar alignment by watching polaris track round the circumference of the circle while you rotate the mount head (you are probably not trying to do that).  Your 'rough' alignment may be good enough for your purposes on any given night.  If you need a greater degree of accuracy then do a drift alignment following the tutorial that has already been linked.  There are other ways of getting aligned - check out the video on this page: http://www.alignmaster.de/

Purists will tell you that drift alignment is more reliable than software methods.

Also remember that even if you get your polar alignment perfect all this means is that the mount is set up correctly.  You are then faced with the various tolerances built into the mount itself.  Even with a perfect polar alignment, therefore, you will still need to have some form of guiding if you want to get long exposures (unless you buy one of those 10 micron or similar mounts).  My guess is that there will be some folks (ahem, ahem) who started off with only a rough alignment and were able to get reasonably good 5 (and possibly 10) minute subs without getting the polar alignment fully nailed.

[Fenris]

I tried it out last night (finally) and got 4 min exp with 13mm. I know this isn't much of a test, but i only wanted to see how easy/difficult PA would be. Positively supriesed since i have heard that i wouldn't be able to check PA after mounting the camera. I used the L-bracket and just held the illuminator in front of the polar scope. No problem, and i managed to fix the small deviance after attaching the camera and counterweight. With a little modification i should be able to attache the illuminator even with the L-bracket on the mount too (if i bother). This took me about 3 minutes to set up. Now i have to wait for about a week before i can test with longer focal lengths since the weather won't cooperate... Blah...

Astrosurf: really good link. I see that he says that his description is for a fork mount using alt/az but that the same procedure can be used with eq-mounts. I assume i only switch alt/az with ra/dec? But which is which? Does alt=ra and az=dec?

And thanks for all good advice everyone!

[Astrosurf]

I wish I could help. I've never done drift alignment!