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

Bi-monthly release with minor bug fixes and improvements

Relative guiding of moving objects, comets etc

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Hi,
When I use PHD2 I can guide on comets throu a star by relative guiding (as long it fit in the guide window). But now I use the internal guider in Ekos (Astroberry), I can't see that there is something like that built in.

I can change the speed of the RA and DEC motors to match the speed of a comet but then it can not autoguide. What is the best way to change the speed of the motors, change standard setting or is it a way to add a relative extra speed (dRA, dDEC) ?

/Lars
2 years 2 months ago #78961

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Lars

As far as I know, there's no equivalent in the internal Ekos guider to the PHD2 feature called comet tracking openphdguiding.org/man-dev/Tools.htm#Comet_Tracking. I have taken reasonable comet images in the past using Ekos by just using stacks of relatively short exposures that are both registered to the comet and the stars, and by keeping the comet in the frame by moving my pointing after a while, but clearly this would be a nice addition to the Ekos guider for those folks imaging comets.

Hy
2 years 2 months ago #78971

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Hi Hy,
Thanks for the answer. Next time I have a comet visible from my balcony I will do a test with only alter the speed of the RA and DEC motors. My comet images so far I have taken with 30 seconds expsure and with my HEQ5 there is not necessary to guide, but if I could do it's fine.

/Lars
2 years 2 months ago #78978

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I started a topic on this same idea about a year ago. There was some interest, but it did not progress from there.
My recommendation is to stick with PHD2 for comet tracking mode. You can get the dRa and dDec rates calculated from www.minorplanetcenter.net/iau/MPEph/MPEph.html
You will want to choose these options:
Ephemeris interval: Hours (especially for fast moving comets)
Separate R.A. and Decl. coordinate motions
Display motion as: "/hr
When the HTML tables are generated you will be interested in the values under Sky Motion.
Ensure Sticky lock position of OFF in PHD2. Because eventually the guide star will be lost, and a new one will have to be selected elsewhere.

Carte du Ciel can also calculate and send the rates to PHD2 and is INDI compatible.
It certainly would be nice if EKOS could make the same ephemerides calculations and send the values to PHD2 and internal guider as well.
Last edit: 1 year 1 month ago by Andrew.
2 years 2 months ago #78991

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Hi Andrew,
That's almost exact how I did with PHD2 when it was installed in my old Windows server. I wrote a turorial abut it, maybe outdated now:

www.astrofriend.eu/astronomy/tutorials/t...met-autoguiding.html

Today I changed to Astroberry setup on Raspberry. But the problem I got this season is that PHD2 doesn't work anymore in my Astroberry, see my thread:

www.astrofriend.eu/astronomy/tutorials/t...met-autoguiding.html

When I couldn't get the PHD2 work anymore I shifted to Ekos internal guider and it worked very well now with the last update. So I felt it could be good to only use that guider. Very happy with it. But still, it could be a very good alternative to have the PHD2 auto guide to work again.

/Lars
2 years 2 months ago #78994

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Great tutorial!
I found your thread regarding your PHD2 issues. I left some troubleshooting advice there.
2 years 2 months ago #78996

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These days I shall take photos of a comet with KSTars/INDI.

Not with relative auto guide, only change the speed of the RA/DEC to match the comet.

On this page of EQMOD mount driver there is a button for custom Track.



But I can't find anywhere to put in these dRA and dDEC figures. Anyone who knows ?

/Lars
Last edit: 1 year 3 months ago by Lars.
1 year 3 months ago #89077
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Tonight I could do some testing of Custom Track rates in Indi EQMOD. Even if I can't get guiding with relative speed when hunting comets it had been good to be able to set Custom Track Rates.The comet C/2022 E3 ZTF I got (CdC) for the date 2023-01-01 to be =

dRA -0.74arcsec/hour and set Custom RA Track rate to 15.040861444 arcsec/secd

DEC 2' 10.8"/hour and set Custom DEC Track rate to 0.036333 arcsec/sec

But Indi doesn't accept the DEC Custom Rate and I get these error messages when testing different Custom Rates.



The correction must be bigger than 0.8 arcsec/sec to be accepted. Yes it's a small correction, but when follow the comet for hours it does matter if I can use Custom Tracks.

ps.
Is it correct to ask this question here at Astroberry embedded Indi or should I ask at Indi / Mount ?

Happy new year to all of you !

/Lars
Last edit: 1 year 2 months ago by Lars.
1 year 2 months ago #89334
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I must correct an error I made in my earlier instructions on obtaining comet tracking rates.
I have since learned that the correct rates are provided by the Minor Planets Center option "Separate R.A. and Decl. coordinate motions"
The values for dRA provided by the option "Separate R.A. and Decl. sky motions" are incorrect for our purposes.
I had concluded it was appropriate because it was in line with values provided by Cartes Du Ciel and the JPL Horizons system. They they are all incorrect!

JPL Horizons, CDC, and MPC 'sky motion' option all provide figures as dRA*cosD, not simply dRA. To correct them, one would need to divide their values by the cosine of the declination in degrees.

It is rather surprising to me that this is not a well documented consideration, and that a rather good program such as Cartes du Ciel would make this error. But it absolutely must be taken into account with comets at high declinations.
1 year 1 month ago #90516

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Hi Andrew,
You must anyway transform the dRA and dDEC to correct format. From hours to sec. I have setup a calculator on my homepage were this can be done. Also the Cos(DeC) is included if needed.

Many yaers ago when I used PHD2 there was a problem when CdC transferd the data to PHD2, the Cos(DeC) was missing, but that is corrected since many years ago. You don't that is do that, it only dosply the result. But many years since I used PHD2, can be different now.

ps.
I have made a fix in the EQMOD INDI driver that let me setup dRA and dDEC, there was an error, the lower limit blocked that slow speeds that was necessary for comets. I haven't had any clear sky yet so I haven't tested it yet.

/Lars
1 year 1 month ago #90582

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Hi Lars.
PHD2 comet tracking takes arcsec/hour so no need to convert it.
You might be thinking of the ASCOM EQMOD custom tracking rate feature wich takes a side loaded file. That method uses Arcsec/sec along with time stamps for variable rates. If you need those units, the MPC service has the option to output them.

Clear Skies!
1 year 1 month ago #90583

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Hi Andrew,
My calculation on the homepage is more general to take care of the most devices. For me, I use the EQMOD INDI the last years. I take the comet data from CdC and get it in degree, minute and seconds per hour. Transform that to arcsec/sec in decimal form, and if needed a Cos(Dec) adjustment.

Lars
1 year 1 month ago #90606

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