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Astrotrac polar alignment?


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Hello I was out with the astrotrac for the first time and found polar aligning it abit of a faff, I lined up Polaris into the indicated position, my question is the extended lines that go to the stars in Ursa Major and Cassiopeia how accurate do these have to line up? As it can be hard to see as you can't see the constellations in the polarscope?

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You won't be able to see ursa major in the polar scope. If you can't see the other two alignment stars as indicated in the manual, and you need a more accurate polar alignment, you'd probably need to drift align or some such varient.

There is no such thing as very accurate, quick and cheap polar alignment in my limited experience; it takes time.

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As already mentioned above, you can't actually see any of the constellation stars in the polar scope. It wasn't very clear to me when I first started polar aligning the AstroTrac, but after a few attempts you get to grips with it. What can confuse things a bit is that when looking through the polar scope, everything is inverted, so up is down, left is right etc.

Here's the procedure I follow:

1) Find Polaris and aim the tripod north. I try to do it with one tripod leg facing north.

2) (optional) Level your tripod if it has built in levels.

3) Rotate the polar scope arm out and kneel back looking though the hole in the polar scope arm.

4) Without the polar scope fitted try to get Polaris in the middle of the hole by moving the tripod and adjusting the alt/azi or equivalent of your geared head. Move your head back and forth to use parallax to align it as close as possible.

This gives you a coarse alignment with Polaris.

5) Attach your camera and lens and point it in the direction you are going to image.

6) Insert the polar scope into the polar scope arm and turn it on, not too bright.

7) Find Ursa Major and Cassiopeia with the naked eye.

8) Look through the polar scope and rotate it until the illuminated reticule matches how you see them positioned in the sky.

9) Adjust the alt/azi controls of the head until Polaris is in the gap. At this point you will also be making slight adjustments rotating the polar scope.

This gives fairly accurate alignment with Polaris.

10) Turn the polar scope off, or set it to very dim (see below).

11) If you look through the polar scope you should at least see the second alignment star, roughly in position. I can see it from my light polluted garden with a street light blasting in my face. If you can't see another star, even with averted vision, then you can't continue.

12) If you can see the 2nd star, make sure the polar scope is very dim

13) Tweak the alt/azi adjustments and try to get Polaris and the 2dn star in place, you will have to rotate the polar scope as well slightly to achieve this.

14) Once the 2nd star is aligned, do the same with the 3rd star, it is fainter and harder to see, but even this one I can see out my light polluted back door

15) Each iteration will be a smaller and smaller tweaks to the alz/azi controls and rotation of the polar scope.

Once you have all three stars in position, it is as good as it gets. Don't forget to turn off the polar scope.

Alternatively learn how to do drift alignment.....which I currently don't use due to not having views of the south horizon (or any south for that matter).

Some notes:

The 2nd and 3rd alignment stars are quite obvious once you have got Polaris pretty well aligned after step 9 as they should be in the vicinity of the three lines and are the brightest in their respective areas.

The polar scope needs collimating for steps 5 and above to be of any use - see here: http://stargazerslou...t/#entry1858491

The polar scope arm needs aligning for steps 10 to 14 to be of any use.

The polar scope can be dimmed further by removing the illuminator and inserting a tiny piece of paper/sticker in front of the LED

Make sure you use some method of retaining the polar scope to prevent it from falling if knocked. Many people use pipe lagging to keep it in place, I use a lanyard. See here: http://www.progressi...a1298471fb52ffc

Main thing is to practise, the more you do the easier it becomes.


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