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Polar Alignment

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#1 Pete GLA

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Posted 28 February 2010 - 07:43 PM

Hello All,

I'm wondering, after setting up and doing a 2 Star Align followed by a 3 Atar Calibration...followed by a Polar Align...And redoing the 2 Star Align with 3 Star Calibration.

Is there a benefit to do a 2nd Polar Alignment?

And do for the 3rd time a 2 Star Align...followed by a 3 Star Calibration?

This thought has come to me (given that 90% of the time it is cloudy and the mind just seems to be wondering).

Thanks for your time,
Pete

#2 drksky

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Posted 28 February 2010 - 08:31 PM

Only advantage I could think of for doing a repeat polar alignment would be to increase the alignment's accuracy.

#3 JadeSmith

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Posted 01 March 2010 - 11:01 AM

If I'm doing AP, I usually do 2 polar alignments. So far, I have not had to drift align using this method and it's close enough that my SSAG can keep up with any errors.

#4 CounterWeight

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Posted 01 March 2010 - 11:14 AM

Just curious which mount you are using, if permanent mount and do you have a PA scope. There's a process somewhat like you describe called iterative polar alignment. I used a modified Kochab clock, half distance version. Agree with above post, with my CGE (when it works) doing 2 iterations worked well enough for doing 9-12 minutes guided (in reality my LP encroached too much above 9 minutes most nights).

#5 Chris Rowland

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Posted 01 March 2010 - 12:12 PM

It's my opinion that multiple align - polar align cycles will not give any real benefit.

Each cycle will give slightly different results because of slightly different errors in centering stars but the second or subsequent alignment errors won't actually be better, just different.

Chris

#6 Pete GLA

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Posted 01 March 2010 - 04:21 PM

I have a CG-5 GoTo mount. I haven't tried the 2nd Polar Align yet, but, my guess is that it will improve on tracking and have less field rotation...

I'm a new kid in the Equatorial Mount, so I'm asking the more experienced, if it's worth the extra 15min-20min for the 2nd Polar Align, especially on the AP side.

I've not upgraded the software.

Thanks for your input,
Pete

#7 Chris Rowland

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Posted 01 March 2010 - 05:08 PM

My alignment technique is:
Do a two star alignment plus calibration stars.
Stop adding calibration stars when the next one is under the cross hairs of the reticle.
Do a polar align, following the instructions for choosing a star near the meridian.
Use the scope, including for imaging.

My evenings are too short and too rare to spend most of them aligning.

I do use the very latest software.

Chris

#8 neptun2

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Posted 01 March 2010 - 08:22 PM

As far as i know both the cgem and cg5 do not have polar scope included so initial polar alignment error can be pretty big. If so the dec drift of the stars due to polar misalignment can be pretty fast during the first 2-star align.This in turn can make it difficult to precisely center the stars. so i think that second goto alignment and polar align adter the first ones is a good idea if you intend to do long exposure astrophotography.

#9 Pete GLA

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Posted 01 March 2010 - 09:03 PM

My evenings are too short and too rare to spend most of them aligning.

Chris


Chris,
I'll 2nd & 3rd that. Since Nov 17th, I've gone out 3 times.
The wx man is forecasting clear skies this Wed-Sat.

I usually get out the Nexstar 8SE for visual observation...
The CG-5 I'd like to use it for AP. (I prefer the CG-5 for visual as well, since it being more stable than the Nexstar mount).
So if there are ways of making the CG-5 more precise in Alignment, Slewing and Tracking, (for AP nights) it is worth the time and patience.
Considering that I must set-up and tear down each observing session, it does make me want to get up and run as quickly as possible.
This is the advantage of the Alt-Azm mount, quick set-up and very convenient/comfortable positions for observing.

Once again thanks,
Pete






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