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INDI Library v1.8.3 Released (02 Jan 2020)

Minor monthly bugfix release with a new RainbowAstro mount driver and improved pier side simulation.

Problem with polar alignment in southern hemisphere?

6 days 20 hours ago
wvreeven
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Problem with polar alignment in southern hemisphere? #48057
Dear all,

Recently I moved from Spain to Chile and now I am trying to make use of the clear skies here. I have been setting up my astro photography gear for a few days in a row now for various tests and I noticed several times a problem with polar alignment. After the three images have been taken and the mount has rotated twice, the pink line is drawn to indicate how a star should be moved using the fine tuning knobs of the mount to improve the polar alignment. I notice that I need to aim the line such that the end point is on top of the star and the start where the star should end up. If I do this the other way around, the polar alignment will get worse. Has anyone else noticed this?

I have attached the logs of today's session for reference.


Clear skies, Wouter

ASI1600MM-Pro Cooled and filter wheel with a SkyWatcher Esprit 80 ED on a SkyWatcher HEQ5-Pro

ASI1600MM-Pro Cooled and filter wheel with an 8" TS Ritchey-Chrétien on a SkyWatcher EQ6-R
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6 days 16 hours ago
knro
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Problem with polar alignment in southern hemisphere? #48060
There has been various reports about it being flipped before, and so I added a flip to reverse the effect. Maybe this is what caused it?
// JM 2019-08-17: Flip for southern hemisphere.
// Possible fix for: https://indilib.org/forum/ekos/5558-ekos-polar-alignment-vector-backwards.html
correctionVector.setP1((hemisphere == NORTH_HEMISPHERE) ? celestialPolePoint : RACenterPoint);
correctionVector.setP2((hemisphere == NORTH_HEMISPHERE) ? RACenterPoint : celestialPolePoint);

Frankly, I still don't understand why it is reversed on some occasions. Perhaps someone can figure this out? It's been an issue for some users even since the PAA was introduced.

Jasem Mutlaq
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6 days 13 hours ago
ChrisRowland
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Problem with polar alignment in southern hemisphere? #48064
Just a thought...
Moving to the Southern hemisphere has the effect of rotating the images by 180 degrees and maybe the direction vector is also rotated.
Another thing that rotates the image is a pier flip and maybe it would be different if the mount were on the other side of the pier when the images are collected.
That should be easy to test.

Having a diagonal (actually an odd number of reflections) in the image chain will flip the image and that could also have an effect.

I can't test because I can't see the pole from where I usually set up and the PAA assumes you are looking at the pole. I don't think that's essential, the three images could be any distance from the pole. It's on my list of thigs to try, but it's a long list and it's very cloudy in the UK.

Chris

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6 days 10 hours ago
wvreeven
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Problem with polar alignment in southern hemisphere? #48067
Thanks Jasem and Chris for the quick replies.

Jasem: yes I remember that people had issues with it, but that never affected me before. I don't understand where this comes from either but I never inspected the code. Perhaps some checkbox in some advanced section of the configuration ("Warning: only tick this if you know what you are doing") that reverts the direction of the pink line could help until we get to the bottom of this?

As for Chris's reply: I don't have a diagonal in my optical train. I use a refractor with a field flattener and the camera directly attached to it without any reflecting devices, so if that were an issues then at least I am not affected by it. I can test what happens if I let the telescope move to the east side of the pier but I did test with going west first and then going back to the east ending in the park position via the polar alignment routine (i.e. autopark is disabled).


Wouter

ASI1600MM-Pro Cooled and filter wheel with a SkyWatcher Esprit 80 ED on a SkyWatcher HEQ5-Pro

ASI1600MM-Pro Cooled and filter wheel with an 8" TS Ritchey-Chrétien on a SkyWatcher EQ6-R

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