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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Re:New Polar Alignment Scheme and Features

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I'm not totally confident.

AIUI you are saying that because the reference star you are aligning on is refracted the pole position correction must be refracted. I'm very unconvinced about that because the refraction error of the reference star will depend on where the star is. A star that's in the South will have a refraction error that is opposite to a reference star in the North.
I think that polar aligning to a couple of arc minutes is plenty good enough for a portable set up. Getting better than that would need something like the TPoint method available with the Software Bisque mounts where a precise alignment is determined using about 100 stars, then the mount is adjusted using the high precision mount screws
3 years 1 month ago #66749
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Regarding the new Polar Alignment Scheme and crossing the Meridian, my Avalon M-Zero OBS (with the motorized polar alignment system) went through the procedure without problems as it does not need to flip when it crosses the Meridian. It went from Pollux, across the Meridian, to an area close to the Pleiades, and the correction triangle help me correct in altitude very easily. I have a small problem with the azimuth control so I did not do the correction on it, but being about 20' from the Pole, I can live with that until the -20C changes to a more pleasant temperature so I can try to fix the problem.

Great work, thanks a lot.
3 years 1 month ago #66763
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Yes, of course. I was especially referring to the case that you align close to the pole. Then your reference star will also be close to the pole, and the main offset will be the refraction at the pole. The remaining error would be the differential refraction within the FOV of the camera, but that is in the range of arc seconds (±1.5 for a FOV of 2 degrees at my LAT 29).

You are indeed correctly stressing the fact that what pole you align to only depends on the reference star that you use for correction. I had initially assumed one would get different results for the PAE whether the measurement is done close to the pole or at low declination. But indeed, it always computes it in JNow, so it should always be the same error (modulo some small error coming from differential refraction).


Yeah, even my permanent mount is some 4-5 arc min off, I had not bothered to fine-tune it better. I will do, next time I'm up, if only to test the new PA routine. But you wouldn't need TPoint for good PA. That is really only needed for perfect pointing/goto. But who needs that nowadays with StellarSolver and Slew-to-Target :P.
OK, and for unguided tracking.......
3 years 1 month ago #66792
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@Hy

so much work, such a clean code I barely understand at first glance.

Thank you!

This is pedantic, I know, sorry:



Until now I had no clear skies to test the polar alignment routine with my mount.
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3 years 1 month ago #66884
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So I did this last night. I had prepared for some time outside, with warm jacket, gloves etc. - but no need really. Ran the routine, moved the star along the lines (with only 5' PAE they were indeed accurate this time :lol:), then re-ran it for a test: 12" and 13" remaining error. Wow. Almost a pity I'm on a permanent pier and won't use that often....

I checked the guiding afterwards. At the default setting DEC had a min move of 50ms, something like .4". With that I only had a DEC guide pulse every few minutes. I've then reduced it to 30ms to better match the 0.2" of GPG. I left it running for a while, and actually experienced the best guiding I've seen so far, going down below 0.3" total RMS. That was at 2100mm focal length :woohoo:
Too bad I wasn't prepared for imaging. I wanted to test my new Baader FFC and had no guide scope, as I had used parts of the extension tubes of it. So that guiding had been with the main cam/telescope and the FFC (at 2.3 x).

And, needless to say, now that things are so nicely set up for the coming New Moon, we again get weather alerts for massive rain/snow storms.
3 years 1 month ago #66891
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This sounds like a very nice feature ! Many thanks !!!
Currently, due to weather conditions, I am limited to simulation. I am struggling to set up my simulator with deliberate erros. I tried various settings within the "Simulator Config", i.e. PAE, EQ PE, but I only get some misalignemt for "normal" alignment. With the PAA I always get a perfect PA. Can someone hint me in the right direction, please ?
3 years 1 month ago #66910
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@Dirk

This works for me:

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3 years 1 month ago #66921
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Hi all,

I hope you don't mind if I post some more 'stupid/insane challenges'. My observatory unfortunately is in clouds and ice and snow and the road is closed, but last time I was up there I took my old mount with me, a Vixen GP-DX with Synscan EQ5 upgrade. I wanted to play around with it a bit, to set it up as camera lens unit with my ASI183MC. So I have it standing in my office here at sea level.

This afternoon clouds vanished partially. But due to some cabling limitation, I couldn't bring the mount outside. Instead, I had it look through a window:

I pre-aligned the mount looking up the orientation of my appartements wall in openstreetmap and then checked what I can see from there. It's facing SSE and the window opening was just high enough that I could get an approximate 60 degrees arch at declination -20. Yes, aligning to the NCP with reference stars south of the celestial equator...
I did it manually, not using the mount control, to have better control over where I'm pointing. I did one shot close to meridian, one as far east as possible, and a final one between the two. PAE was some 3 degrees, and easy to correct. The star moved perfectly along the guide lines.

Next I reset the mount to home position, made sure the camera is really pointing to the NCP, then checked what I can see there through the window. I wanted to try Thors Helmet area, but that was already too high. So I aimed in Canis Major where the DSS image showed some nebulosity. Well, I didn't really see it in the image. That was too much of a challenge maybe. It's not perfectly in focus either. But this is a 120s exposure, unguided. Only at 135mm FL, but the PA definitely worked really well even under this more than extreme conditions.

Hy, this is absolutely amazing work of yours! If you're able to see stars, your routine will do PA :woohoo:

3 years 1 month ago #67023
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Hy,

Today I installed the latest nightly build of KStars and ran the new polar alignment tool from La Serena, Chile. I let the star I chose follow the two lines to end up on the other side of the triangle. Then I ran the polar alignment routine again. It said that the alignment error was 35". I call that a success!

Thank you so very much for implementing this!!!


Wouter
3 years 1 month ago #67096
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Thanks Wouter.

I'd love to add to the Unit Test, some data from South America. Could you please email me a pointer to your log--assuming you had align debugging turned on. If you didn't, could you please generate a log for me?

Also, glad to hear you're back in Chile working on "real telescopes"!

Thanks,
Hy
3 years 1 month ago #67097
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Hy,

I did not enable debug logging but would love to generate the logs for you. Would you like to have data both for a polar alignment error of, say, 1° and a very small one or would a very small one suffice?

Wouter
3 years 1 month ago #67111
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A few different things would be great, e.g. introduce an error then and remeasure. If you can, pointed near pole and away.
3 years 1 month ago #67119
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