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25 Jul 2018
Glad to announce of release of INDI Library v1.7.4 on 2018-07-25. A few drivers were added in this release as we continue to improve & stabilize existing drivers.
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TOPIC: Polar alignment when you can't see Polaris

Polar alignment when you can't see Polaris 3 weeks 2 days ago #29206

Hi

I just saw Ekos and K-Stars and find it to be a very powerful suite for astrophotography. For several years I've been using Sequence Generator Pro in Windows 10 and Ekos seems to be a strong performer as well, with the added benefit of being cross-platform. You can see my gallery here, including one image awarded as Astronomy Magazine Picture fo the Day: www.flickr.com/photos/alfredo_beltran/

I'm located at Bogotá, Colombia at 4.8 degrees north latitude and it's hard to be able to see Polaris from here (sometimes you can). I watched the video of the Ekos polar alignment assistant tool and it makes very easy to have a strong polar alignment as long as you can see Polaris.

Can this assistant be used to polar align your mount when you cannot see Polaris?

Thank you very much for your help,

Alfredo

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CEM60
Celestron 925 EdgeHD Hyperstar
MicroTouch Focuser
Canon T1i modified by Brent Oliver
Bogota, Colombia
www.flickr.com/photos/alfredo_beltran

Polar alignment when you can't see Polaris 3 weeks 2 days ago #29223

Hello Alfredo,

Welcome to INDI & KStars! Impressive gallery you got there!

Regarding Polar Alignment Assistant, I believe you can use the Legacy Polar Alignment tool in Ekos which can work without Polaris. It's just located directly below the regular Polar Alignment Assistant tool.

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Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
Add your observatory info

Polar alignment when you can't see Polaris 3 weeks 2 days ago #29229

Thank you Jasem

How does it work? Is it also by plate solving the image to see how far is the mount from the pole?

Alfredo

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CEM60
Celestron 925 EdgeHD Hyperstar
MicroTouch Focuser
Canon T1i modified by Brent Oliver
Bogota, Colombia
www.flickr.com/photos/alfredo_beltran

Polar alignment when you can't see Polaris 3 weeks 2 days ago #29231

It uses plate solving, but it uses a different method than the regular polar alignment tool. It's not as good, but it at least gives you the error and how to correct it.

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Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
Add your observatory info

Polar alignment when you can't see Polaris 3 weeks 1 day ago #29247

  • Gilles
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I've done polar alignement without polaris yesterday with polar assistant, and it looks to work !....
I've started procedure with my mount pointing to zenith
Then on first frame ekos makes a warning and suggests to slew to polaris : answer no and be carefull...
I suggest to limit rotation to 15°...

It is certainly less accurate, but it works.
Will retry asap
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Last Edit: by Gilles.

Polar alignment when you can't see Polaris 3 weeks 1 day ago #29254

albeltrang73 wrote: Hi

I just saw Ekos and K-Stars and find it to be a very powerful suite for astrophotography. For several years I've been using Sequence Generator Pro in Windows 10 and Ekos seems to be a strong performer as well, with the added benefit of being cross-platform. You can see my gallery here, including one image awarded as Astronomy Magazine Picture fo the Day: www.flickr.com/photos/alfredo_beltran/

I'm located at Bogotá, Colombia at 4.8 degrees north latitude and it's hard to be able to see Polaris from here (sometimes you can). I watched the video of the Ekos polar alignment assistant tool and it makes very easy to have a strong polar alignment as long as you can see Polaris.

Can this assistant be used to polar align your mount when you cannot see Polaris?

Thank you very much for your help,

Alfredo


Maybe I am wrong here, but I think if you are using a wide angle camera like the QHY polemaster (11x8 degrees) and just point it towards the North Pole you should catch enough cricumpolar stars to allow polar alignment with the polar alignment tool in Ekos. Only if you have a narrow field and bad visibility you probably might still have problems.

Let me know fhat makes sense. As long as the solver can find something, the alignment tool should work, I would think.

Jo

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Polar alignment when you can't see Polaris 3 weeks 1 day ago #29256

Hi Jo

That’s a very good suggestion.

In fact I have a wide FOV because I use hyperstar with a C925 EdgeHD and a DSLR, so I can have several degrees of sky covered in one shot.

The issue is that Polaris is very low here, at roughly 5 degrees above the horizon and isn’t always seen because of clouds. Besides, I suspect the apparent position of the refracted pole would cause alignment errors.

That’s why I prefer an alignment method that doesn’t require direct watching Polaris, if possible.

Alfredo

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CEM60
Celestron 925 EdgeHD Hyperstar
MicroTouch Focuser
Canon T1i modified by Brent Oliver
Bogota, Colombia
www.flickr.com/photos/alfredo_beltran

Polar alignment when you can't see Polaris 3 weeks 1 day ago #29257

Thanks Gilles

How big would be the error with this approach?

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CEM60
Celestron 925 EdgeHD Hyperstar
MicroTouch Focuser
Canon T1i modified by Brent Oliver
Bogota, Colombia
www.flickr.com/photos/alfredo_beltran

Polar alignment when you can't see Polaris 3 weeks 1 day ago #29258

albeltrang73 wrote: Hi Jo

That’s a very good suggestion.

In fact I have a wide FOV because I use hyperstar with a C925 EdgeHD and a DSLR, so I can have several degrees of sky covered in one shot.

The issue is that Polaris is very low here, at roughly 5 degrees above the horizon and isn’t always seen because of clouds. Besides, I suspect the apparent position of the refracted pole would cause alignment errors.

That’s why I prefer an alignment method that doesn’t require direct watching Polaris, if possible.

Alfredo



Clouds are indeed a problem. Otherwise it should not matter whether you see Polaris or not, as long as you see other circumpolar stars and the solver can recognize them.

It may work with a normal 50mm lens on a DSLR mounted to your dovetail. Generally, the closer your chosen alignment star is to the pole the smaller the alignment error should be in the end because of the earth's rotation between measurements and mount adjustments. The largest error would result if you measure near the Zenith in your case.

Does that make sense?
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Polar alignment when you can't see Polaris 3 weeks 1 day ago #29259

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albeltrang73 wrote: Thanks Gilles

How big would be the error with this approach?


I don't know !
I've just noticed that when moving ALT/AZ knobs on final step, it's harder to reach target

it was just a one time test :
And I'm affraid i'm not able to reproduce with simulators :S
Impossible to solve first frame whatever i do.
Need to think again to what i've done before ...

Gilles.

Edit : i think i've found
Polar assistant can be done only with declinations between 60° and 90°
Otherwise solver will fail each time.
This limitation is certainly to make polar assisant go faster, but it might be increased somewhere for specific locations like you
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Last Edit: by Gilles.

Polar alignment when you can't see Polaris 3 weeks 1 day ago #29262

El Corazon wrote:
Generally, the closer your chosen alignment star is to the pole the smaller the alignment error should be in the end because of the earth's rotation between measurements and mount adjustments. The largest error would result if you measure near the Zenith in your case.

Does that make sense?


It totally makes sense. Thanks. I'd have to try and see how accurate are the results.

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CEM60
Celestron 925 EdgeHD Hyperstar
MicroTouch Focuser
Canon T1i modified by Brent Oliver
Bogota, Colombia
www.flickr.com/photos/alfredo_beltran

Polar alignment when you can't see Polaris 3 weeks 1 day ago #29263

Gilles wrote:
Edit : i think i've found
Polar assistant can be done only with declinations between 60° and 90°
Otherwise solver will fail each time.
This limitation is certainly to make polar assisant go faster, but it might be increased somewhere for specific locations like you


This is good enough. Gilles!

At a declination higher than 60 degrees could work from here.

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CEM60
Celestron 925 EdgeHD Hyperstar
MicroTouch Focuser
Canon T1i modified by Brent Oliver
Bogota, Colombia
www.flickr.com/photos/alfredo_beltran
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