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Help me up my polar alignment game?

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#1 pdfermat

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Posted 10 October 2013 - 09:11 AM

Here's my current polar alignment routine I use with my Altas (I should preface this with the fact that I have verified that my PAS is properly aligned):

1. Center Polaris in the crosshairs of the PAS.
2. Move the mount in altitude only until Polaris intersects the perimeter of the big circle in the PAS at the 6:00 position.
3. Move the mount in RA until Polaris is in the little circle of the PAS.
4. Set the RA setting circle to 0 and tighten.

I've only done 1-4 once (twice actually - to verify), now each time I align I:

5. Rotate the mount in RA until the correct hour angle of polaris shows on the RA setting circle (I get the hour angle from either EQMOD or the hand controller).
6. Use the mount's alt-az adjustments to put Polaris in the small circle of the PAS.
7. Tighten everything down and re-verify Polaris is where it should be in the little circle.

So I thought I was getting good at this - visually it seems my tracking is spot-on. What is making me think I've got to "up my game" is that I just started learning how to autoguide.

I'm using the Orion SSAG and PHD. For my maiden autoguiding voyage last night, I was able to get everything working, but I'd hear a DING! from my laptop about every 5 seconds. I know this is the guiding software telling me it is making and adjustment, but I feel like that many adjustments that often is indicative of poor polar alignment.

Here's the one caveat though - I don't have the correct shoe to mount the mini guide scope on my C8 (it's on the way), so I'm guiding the scope through the C8. I'm guessing that this puts a much stricter tolerance on the guiding in general due to the very long focal length.

Anyway - any suggestions to help me become a better polar aligner? The hand controller has an enhanced polar alignment routine, but I'm hesitant to use it because I've read that it has bugs in it due to the new EQ-G pro mount/firmware compatibility. I'm thinking maybe my next move should be diving into the polar alignment routine that goes along with EQMOD.

#2 TxStars

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Posted 10 October 2013 - 09:34 AM

Guiding with the c-8's 2032mm focal length on most small mounts is going to show every step you take and every breeze in the air.
That said any polar alignment error is also magnified.
If you must use the c-8 then just worry about large movements north & south to begin with.

#3 Cliff Hipsher

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Posted 10 October 2013 - 11:10 AM

At some point during your polar alignment you should be prompted to use the hand controller to center Polaris in the eyepiece. This is were a high power illuminated reticule eyepiece with dual cross hairs will be worth its weight in gold.

Also, keep in mind that if your mount is slewing to a star other than Polaris, you are not doing a Polar, you are doing a sky alignment... A Polar alignment affects tracking, and therefor guiding. A sky alignment affects the pointing model and in some cases cone error both of which have an affect on GoTo accuracy....

#4 Footbag

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Posted 10 October 2013 - 11:22 AM

The bottom of the linked page shows a method of polar alignment using PHD guiding. I've used it many times and it's my preferred method.

It allows you to see drift in smaller increments then you would otherwise. So you can make corrections every 10s rather then waiting 1-5m.

http://njstargazer.o...arAlignment.asp

#5 rmollise

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Posted 10 October 2013 - 04:37 PM

Your polar alignment would have to be way off to cause constant loss of the guide star. Look to your guide program settings and your connection to the mount.

#6 Phil Sherman

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Posted 13 October 2013 - 09:02 AM

A correction every 5 seconds is not unusual. I get that most of the time with my Atlas, even when my polar alignment is off by less than 2' of arc. This is caused by PhD correcting for periodic error in the mount's drive train.

It's not possible to get the mount perfectly aligned in altitude using the center of the alignment circle in the polar scope. This is an effect of atmospheric refraction which shifts Polaris a bit towards the N horizon. The amount of the effect is a function of your latitude.

You'll need to learn how to perform a drift alignment to improve your polar alignment. Once you start using drift alignment, you'll discover that it's important to level the tripod before attaching the mount. Doing this decouples the altitude and azimuth adjustments from each other and makes the iterative drift alignment process a lot easier.

Phil






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