#21  
Old 22-02-2010, 03:28 PM
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Another Polar Alignment Method

Hi Tim

I don't believe that it would be that critical for the mount to be dead set level but also depends on how far you were out when making the passes.
Last night I went out and did some further testing, see my last posting.
I feel it's more likely to be Alt position as I found this can really play havoc with this method when testing last night.
Once I returned the Alt back to the setting I originally had I was able to get Epsilon and Beta to pass through the cross hair.

Cheers
Dave
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  #22  
Old 26-02-2010, 02:39 PM
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Quote:
Originally Posted by Davelrkn View Post
Hi Tim

I don't believe that it would be that critical for the mount to be dead set level but also depends on how far you were out when making the passes.
Last night I went out and did some further testing, see my last posting.
I feel it's more likely to be Alt position as I found this can really play havoc with this method when testing last night.
Once I returned the Alt back to the setting I originally had I was able to get Epsilon and Beta to pass through the cross hair.

Cheers
Dave
I think your right - yesterday I WAS able to get them pretty close - or at least in the center of my telrad. I had a lot of trouble getting it dead center of a reticle though.
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  #23  
Old 27-02-2010, 12:22 AM
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Hi Dave, I tried this method tonight and it works.
I aligned both stars and checked my polar scope and there was octans, slightly off though my mount was a little off level but still very close.


Cheers Daniel.
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  #24  
Old 27-02-2010, 03:41 AM
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telemarker (Keith)
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Dave, I tried this method tonight and my mount was way off when using the crosshairs on the finder (on both the Alt and Az settings). What I did do though was to adjust one star with alt, move to the other and adjust the azimuth. By moving between the stars and adjusting only one setting at each of the stars, I had them passing through the crosshairs on a RA traverse in a couple of minutes. I'll try this again soon to see if I can replicate it.
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Old 27-02-2010, 06:40 AM
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Dave, I tried this method tonight and my mount was way off when using the crosshairs on the finder (on both the Alt and Az settings). What I did do though was to adjust one star with alt, move to the other and adjust the azimuth. By moving between the stars and adjusting only one setting at each of the stars, I had them passing through the crosshairs on a RA traverse in a couple of minutes. I'll try this again soon to see if I can replicate it.
This is a correct way to do it.
However, the method will converge faster if you do polar axis elevation correction on whichever star is lower or higher in the sky.
The azimuth of the polar axis is then done on the other (whichever is more to the east or west).

Ideally, the stars should have RA difference of ~6 hours... and at the time the alignment is done they are positioned in the sky such that one is exactly above or under the SCP and another one to the left or right.

BTW, this method of polar alignment is exactly equivalent to the use of polar scope, except the above mentioned stars are much brighter than Octans stars and the accuracy could be better if higher magnification eyepieces were used. However, to achieve the maximum accuracy, the DEC difference between the two stars (01'40" or ~1/20 of Moon diameter) should also be considered and eventually corrected.

Last edited by bojan; 28-02-2010 at 08:16 AM.
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  #26  
Old 28-02-2010, 12:18 AM
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another star pair

another pair of bright (mag 2) stars that are close in DEC (1'51" apart) and meet the 6 hour criterion are:

mirzam in Canis Major (west of Sirius) and diphda in Cetus.

I'll try them out when the rain stops in Alice Springs!
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Old 28-02-2010, 12:28 AM
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Thanks for the explanation Bojan. Sort of puts the method to my madness

That's interesting Andrew, handy to know. Might look to compile a list of pairs to use later in the year while the cloud is hanging around.
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Old 28-02-2010, 08:54 AM
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... BTW, this method of polar alignment is exactly equivalent to the use of polar scope....
However, to achieve the maximum accuracy, the DEC difference between the two stars (01'40" or ~1/20 of Moon diameter) should also be considered and eventually corrected.
This way of thinking could be extended a bit further, by designing a special reticle with double cross-hairs in the eyepiece, positioned such that the difference in DEC for specific stellar pair (and specific telescope FL) is accounted for.
In this case, the pair does not have to be exactly at the same DEC, as long as it could fit in the same FOV.

Last edited by bojan; 28-02-2010 at 02:21 PM.
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  #29  
Old 28-02-2010, 09:49 PM
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Hi Everyone
Thanks to all those that have given this method a try and posted ideas suggestions.
Daniel glad to hear you have had some success with this method.
Andrew will have a look at the two stars you mentioned and give it ago when the clouds part here in Bris.
Bojan that's interesting you saying that this method is equivalent to the Polar Scope method, never thought of it that way but you right.
I found the other night it was a lot easier to find Epsilon by doing an alignment on Acrux and by moving the scope in Dec to the North, Epsilon came into view of the finderscope.

Cheers
Dave
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  #30  
Old 02-09-2014, 12:42 PM
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Has this thread died a natural death.

May have to give this method a go tonight if the clouds piss off
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  #31  
Old 02-09-2014, 01:49 PM
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Thx Peter, I am glad u bought this thread back to life, it was so interesting.
The first I have heard of it and Bojans suggestions of eps for different star sets was good too.
Trevor
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  #32  
Old 03-09-2014, 06:27 AM
PeterEde (Peter)
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I need a cross hair reticle but last night I used my camera's live view. It was late and I cant see stars near the horizon. Probably nearer 40 deg high.
Will give it another go tonight. Earlier I at least got a star to follow vertically.
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  #33  
Old 03-09-2014, 07:59 PM
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Guys,

I am always looking at different methods to quickly polar align.

My scope is slightly different - it's on a horseshoe equatorial mount without GOTO.

If I assume that my latitude adjustment is fine, how would it work with my mount?

Image of scope here:

https://www.flickr.com/photos/johnka...57594183210993

Complicating matters, the scope has a rotating truss nose.

John K.
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