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Old 26-08-2020, 01:59 PM
morls (Stephen)
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Selecting Polar Alignment stars

Hi,

I've been having a lot of trouble setting the elevation when doing a polar alignment (NEQ6/SynScan). Up until now I've been unconcerned about how close to SCP the alignment star is, but maybe this is contrubuting to my difficulties. I'm now wondering if I need to change which stars I use for this.

Should I try to find an alignment star close to the SCP?

Cheers
Stephen
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  #2  
Old 26-08-2020, 04:19 PM
Startrek (Martin)
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Stephen
Here ya go ( see Synscan procedure below )

NB: I used Atria and Hadar the other day for polar alignment ( 7.30pm to 8.30pm )
Atria as the polar alignment Star
Atria and Hadar as 2 star alignment Stars

Synscan Polar Alignment Routine V3 and V4 Skywatcher EQ Mounts
( A view of the South Celestial Pole is not required for this Polar Alignment method )

1/ You will be using a 2 Star Alignment to start the process so nominate your 2 Alignment Stars on the same side of the meridian, one of which will be your Polar Alignment Star ( Alignment Stars should be fairly bright stars where possible to ensure they appear in the Synscan hand controllers data base, usually greater than magnitude 2.5 )
(Alignment stars for polar alignment ideally should be located between 35 degrees and 70 degrees in Altitude and no more than 50 degrees in Azimuth from the meridian) Important - Your Polar Alignment Star or 1st Star Alignment Star will be the one closest to the south meridian. To assist with locating and nominating your Alignment Stars use a Star Chart, a Planetarium like Stellarium or Cartes Du Ciel.
2/ Complete a 2 Star Alignment generally in accordance with Syncan 2 Star Alignment procedure. Start with your 1st Alignment Star close to the south meridian ( this will be your Polar Alignment Star as well ) and then 2nd Alignment Star away from south meridian no further than 50 degrees in Azimuth
3/ After completing a 2 Star Alignment press “Menu” then “Alignment” then “Polar Alignment” and then “Enter”
4/ The screen will display “ Select Star”. Scroll through list of stars until you find your previous nominated Polar Alignment Star and press “Enter”
5/ Mount will slew to the selected Polar Alignment Star
6/ Use direction keys on the hand controller to centre the Polar Alignment Star in the telescope eye piece reticle or Computer screen reticle. Once centred press “Enter”
7/ The hand controller screen will now display the polar alignment error ( degrees: minutes: seconds) then press “Enter” to proceed
8/ The mount will now slew to the new Altitude position. Now use the Altitude adjustment bolts only to move the Star to the closest point to the centre of FOV on the reticle eye piece or computer screen reticle. Remember this position and then press “Enter” to show the new polar alignment error ( degrees: minutes: seconds )
9/ Press “Enter” again and mount will slew to the new Azimuth position. Now use the Azimuth bolts only to move the Star to the closest point where the Star was centred in step 8. Press “Enter” to show the new polar alignment error
10/ Press “Enter” again to end the Polar Alignment procedure
11/ Go back to the “Alignment” menu in the hand controller and execute another “2 Star Alignment”. 1st Alignment Star will be your Polar Alignment Star which you should be already centred on from the previous Polar Alignment routine and 2nd Alignment Star is further away from the south meridian.Once the 2 Star Alignment is completed , the polar alignment error will be displayed on the hand controller ( degrees: minutes : seconds )
12/ Repeat the above procedures ( iterations) 2 or more times as required to reduce your polar alignment error below 1 arc second in both Altitude and Azimuth.
Polar Alignment Error displayed on hand controller should show as many zeros as possible
Eg: 1 arc minute error 000 01’ 00” Eg: 20 arc sec error 000 00’ 20”
Try and get below 1 arc minute error in both Altitude and Azimuth if conditions and time permit.
13/ Note: you must perform a 2 Star Alignment before you start with a Polar Alignment routine each time
14/ To improve accuracy of your Star centering and alignments , de focus the star slightly into a small donut shape, this way you can perform more accurate centering operations looking into your reticle eye piece or at your computer screen reticle
15/ The 2 Star Alignment stars you use for Polar Alignment maybe different from 2 Star Alignment stars you use for locating objects ( Goto) as the accuracy of Goto may improve with a wider distance between alignment stars in Azimuth.The 2 Star Alignment stars for Polar Alignment are fairly close to each other near the meridian and only span a small part of the night sky. The Polar Alignment routine obtains better results ( lower error ) when Alignment stars are within 50 degrees apart in Azimuth and closer to the south meridian at between 35 degrees and 70 degrees in Altitude.
16/ With some experience the Synscan Polar Alignment routine can usually be completed with sub arc minute PA error in around 15 to 20 minutes depending on seeing conditions
17/ Note: Star Alignment and Polar Alignment are two different processes
Star Alignment is used to tell the mount exactly its location in the night sky on an object using singular or multiple pointing model algorithms.
Polar Alignment is aligning the central axis of the mount and telescope to the South Celestial Pole using the Altitude and Azimuth adjustments. Depending on the accuracy of Polar Alignment,the celestial object will remain stationary in the FOV for at least a minute or so before any noticeable drift.
However Polar Alignment and Star Alignment do affect each other when adjustments are made. An adjustment of Altitude or Azimuth affects your star alignment accuracy, that’s why you perform a 2 Star Alignment after PA is adjusted.


Hope the above helps
Martin
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Old 26-08-2020, 04:25 PM
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xa-coupe (Jeff)
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Martin has been helping us noobs with our alignment issues with very comprehensive instructions. One thing I will add to Martin's instructions is to learn where stars are. I am pretty good with the mechanics of everything (other than polar aligning) but it doesn't help if you don't know if you're pointing at the right star!
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Old 26-08-2020, 04:46 PM
Startrek (Martin)
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Quote:
Originally Posted by xa-coupe View Post
Martin has been helping us noobs with our alignment issues with very comprehensive instructions. One thing I will add to Martin's instructions is to learn where stars are. I am pretty good with the mechanics of everything (other than polar aligning) but it doesn't help if you don't know if you're pointing at the right star!
Jeff
Martins instructions do mention to use a star chart or planetarium like Stellarium or Cartes du Ceil to learn to navigate the night sky
This is not to embarrass but to advise as sometimes folk may miss detail when running through procedures
Cheers
Martin
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Old 26-08-2020, 05:31 PM
morls (Stephen)
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Thanks Martin and Jeff. I don't have any problem with 2 or 3 star align, and the polar alignment process itself is going well. It's just that the adjustment using the big bolts is really doing my head in, and I'm starting to think it might be because the polar alignment star I'm choosing is more or less perpendicular to the north-south axis. This means any adjustment of the alt bolts is less directly observable through the eyepiece, if that makes sense.

The detail you've provided is great Martin, so I think I'm going to have a clearer idea of the process for next time. I'm going to try and find a star near the meridian, as close to the SCP as possible. It's cloudy here at the moment, but looking at Stellarium it seems Atria might be a good candidate. In the past I've been using Spica, and I think this is just the wrong star to be using for a polar alignment.
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Old 26-08-2020, 05:34 PM
morls (Stephen)
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Ha, I've just re-read the start of your post Martin, and you mention Atria. I'm glad my thinking is heading in the right direction (quite slowly though...)!
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Old 26-08-2020, 07:04 PM
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xa-coupe (Jeff)
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Quote:
Originally Posted by Startrek View Post
Jeff
Martins instructions do mention to use a star chart or planetarium like Stellarium or Cartes du Ceil to learn to navigate the night sky
This is not to embarrass but to advise as sometimes folk may miss detail when running through procedures
Cheers
Martin

Some of us learn slower than others
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Old 29-08-2020, 06:46 AM
Cyberman (Rob)
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This may be a silly question. Is the sequence SA,PA,SA,PA,SA,PA,SA or is it SA,PA,SA, SA,PA,SA, SA,PA,SA. ( PA=Pol All, SA=Star All), Thanks, Rob
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Old 29-08-2020, 07:17 AM
Startrek (Martin)
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Sequence below
Example stars ( Atria and Hadar )
Star alignment stars choose Atria (1st Star) and Hadar ( 2nd Star )
Polar alignment choose Star Atria ( closer to meridian)

Do Star Alignment > alignment successful > error shown
Select Polar Alignment > iteration process
Do Star Alignment > alignment successful > error shown ( Error should be reduced)
Select Polar Alignment > iteration process
Do Star Alignment > alignment successful > error shown ( Error should be smaller again )

And so on ..............

As soon as you adjust the Alt and Az bolts in the Polar alignment iteration process , your Star alignment has been affected by this mechanical change in the mounts orientation. That’s why you have to do a Star alignment again

Hope the above makes sense

Cheers
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Old 06-09-2020, 02:24 PM
Cyberman (Rob)
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Thanks Martin, I tried again a couple of times at polar allignment. Using Atria (PA star) and Hadar I wasn't able to get alt < 1' 30" although azith got to 30 sec PA error. I then tried using Atria (PA star) and alpha centauri and got to 30 sec PA error in both alt and azimuth after just 2 iterations. I think it was because Hadar was getting too low. It looks like both stars need to be quite high. Cheers , Rob.
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Old 06-09-2020, 08:57 PM
Startrek (Martin)
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Rob
If you read item 1 in my procedure it mentions the recommended altitudes for your PA and 2 star alignment stars
Cheers
Martin
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Old 07-09-2020, 10:46 AM
Wilsil (Wilco)
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I tried a few times to get a PA, but failed miserably. Remember I am a newby. :-)
Then I read this topic and saw different stars being used.
I used Alpha Centauri and Arctures because they are bright and easily recognisable. But they are far away from each other, that might have been the problem.
Next time I will see if Hadar and Atria are visible for me.
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Old 07-09-2020, 12:14 PM
morls (Stephen)
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I had an interesting night of alignment last night. I got to about 30" on both axis, but then the fun started. After doing the star align, I went to polar align, did the centreing with hand controller, after which the routine is usually to adjust with bolts after the mount slews a little. Except in this case there was no slewing, but instead the sequence was centre with keypad, press enter, no slew but the mesaage on hand controller was still "use bolts to centre". It was already centred! This happened a couple of times.

Has anyone else had this happen? I'm using a 20mm Orion illuminated eyepiece with a f/l of 2700mm. so the mag is 135x. I'm wondering if I need to use the 2x powermate for the finer adjustment?
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Old 09-09-2020, 10:08 AM
Startrek (Martin)
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If your down to 30 arc sec error on both Az and Alt then that’s quite tight polar alignment
If you go through the routine a few times and get below an arc minute and the Mount doesn’t move or the star stays stationary, then just press enter and your done, there’s no need to adjust the AZ or Alt bolts anymore. If you do tweak the bolts you may make your error worse by adjusting them.If your getting down to or below 000 00 30 on the handcontroller with both Alt and Az then that’s about as best as you can do, pretty tight polar alignment.
Hope the above helps
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Old 09-09-2020, 10:20 AM
morls (Stephen)
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Big help, thanks Martin.
I'm about to make my first foray into guiding, would 30 arc sec error be tight enough for this?
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Old 09-09-2020, 03:38 PM
Startrek (Martin)
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Guiding is mainly affected by -
1/Atmospheric seeing conditions
2/Mechanical issues with your mount ( Dec backlash )
3/ Focal length of your imaging scope
4/ Cable drag
5/ Image scale of your guide scope and main scope
6/ Guide settings

If your using PHD2 then it can tell you what’s wrong if your guiding is poor and can be one of the items above

For me 30 arc sec error on polar alignment is perfectly ok for PHD2 to correct , I’ve even had good guiding numbers on 1 arc minute polar alignment, it all depends on the items above

Cheers
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Old 14-09-2020, 12:57 PM
Wilsil (Wilco)
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Just to say thanks to Martin (Startrek).
I have used his procedure for the last 2 nights (Friday and Saturday) and had a successful polar alignment.
Subs were 60 seconds unguided without trailing.
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Old 15-09-2020, 07:03 PM
Startrek (Martin)
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Wilco
Glad your polar aligned now
Well done !!
The Synscan PA routine is often missed by folk who have skywatcher mounts as it’s not usually advertised, the supplier or retailers generally just mention the Star alignments ( not Polar Alignment routine )
They usually opt for drift alignment , pole master , PHD2 polar alignment or other software programs which can be costly. I’ve been using the Synscan PA routine for over 3 years now and can be aligned in 10 minutes with 2 to 3 iterations. It’s great because I have no view of the SCP at both my imaging sites
Cheers
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