Plate solving decanters target

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Eyeroll1952
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Joined: Tue May 25, 2021 2:03 pm

Plate solving decanters target

#1

Post by Eyeroll1952 »

I have seen the following issue addressed occasionally but have not seen a satisfactory answer…

Some of the time plate solving and centering on a target works for me but in most cases it doesn’t. I use an EQ6-R PRO mount and EQMOD, and use AstroTortilla for plate solving. What happened last night is fairly typical. I polar align and then tell the mount to go to Arcturus for alignment. In this case it put the star pretty much dead center in the camera. I then hit the plate solve button to see what it will do. It tells me the solve is successful but that I am off by 0.72 degrees. Consequently, it moves the mount to put the star at the bottom of the screen as seen in the picture. This sort of thing happens regularly but the degree if mispointing varies, sometimes it is off by several degrees. Incidentally, if you are trying to read the green bar it says the mount isn’t off much, but this was generated after I hit the plate solve button a second time so the numbers aren’t relevant.

Any suggestions for where to start looking for issues? (No need I think to debate JNOW vs. J2000 since that issue has been covered before on this forum and presumably shouldn’t be an issue.)

Thanks!

Paul
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Eyeroll1952
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Re: Plate solving decanters target

#2

Post by Eyeroll1952 »

Sorry, decenters... Decanters sounds like we're at at wine tasting...
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Re: Plate solving decanters target

#3

Post by admin »

Hi,

that's odd - particularly the size of the error being so large and being variable. The JNOW/J2000 mixup would only account for about 0.15 degrees maximum.

It may be worth checking the Alignment/Sync settings in EQMOD - it can be configured to use a complex pointing model, which may throw off the solve + sync (since the sync is not considered to be a 'this is the current co-ordinates', rather a 'here's another data point for the pointing model'). One thing you can try is to change the plate solve sync settings in SharpCap to 'Offset the mount to center the target', as this avoid the EQMOD sync complexity.

cheers,

Robin
Eyeroll1952
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Joined: Tue May 25, 2021 2:03 pm

Re: Plate solving decanters target

#4

Post by Eyeroll1952 »

Hi Robin,

Below is a screen dump of EQMOD after parking the scope. The first time this problem occured it was indeed an issue with the Alignment/Sync area; once I changed the “3-point + nearest point” to just “Nearest point” and reset the point count the issue went away, but this time it seems correctly set. (I must admit to not having a good feeling for what a lot of these parameters really mean…) If we ever get another clear night I will try your other suggestion.

Incidentally, this is likely coincidental (lucky me), but if I at any time tell Stellarium to sync with the mount it promptly steers off by what appears to be an even 90 degrees…

Paul
eqmod-may-2022.png
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Re: Plate solving decanters target

#5

Post by admin »

Hi,

nothing look badly out of place there, so probably worth trying the offset goto option if you get a chance. You could also try to capture and post here a full SharpCap log that includes a bad plate solving run - the log will contain all the info about things like where the mount was before plate solving, what the plate solve result was, what SharpCap sent to the mount, where the mount thought it was after the solving, etc - usually that is enough to work out what is going on.

No idea on the Stellarium thing - I really tend to only use Stellarium for the pretty pictures - SkyTechX is my preferred planetarium program for controlling the mount.

cheers,

Robin
Eyeroll1952
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Re: Plate solving decanters target

#6

Post by Eyeroll1952 »

Thanks. If this persists I'll capture a log file and upload. I'll look into SkyTechX as well. The only drawback is that I play on both Windows and Mac machines and SkyTechX is unfortunately only Windows.
Eyeroll1952
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Re: Plate solving decanters target

#7

Post by Eyeroll1952 »

Hi Robin,

Still out of luck with the plate solving. Picture shows what it did last night after I told the mount to go to Vega.

TOP ROW: Left is initial position without plate solving. Middle is after plate solving with “Offset the mount…” setting, moved 0.79 deg. Right is after I then did another plate solve with the “Sync mount…” setting. This moved it another ~0.8 degrees to the bottom left off the screen.

Then I told the mount to go back to Vega and repeated the whole process. As BOTTOM ROW shows, this time either plate solve setting resulted in no mount movement.

This seems weird. I am attaching the relevant log file in the hope that you can provide some clue as to what may be happening…

Paul
Stars 20220515A.png
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Log_2022-05-15T20_00_41-1544.log
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Re: Plate solving decanters target

#8

Post by admin »

Hi,

I'm not sure that anything is going wrong here - if we look at the initial co-ordinates before the first plate solve, they are recorded in the log as

Code: Select all

Info   	21:00:51.665876	#1 	Before plate solving mount points to RA=14:14:19,Dec=+19:05:16
These co-ordinates are not the co-ordinates of Arcturus, which is why the plate solve is putting it off center - in fact in the stellarium screenshot below, you can see that with a 2 degree FOV, centered on those co-ordinates, Arcturus is placed distinctly off center.

How did you get the initial co-ordinates sent to the mount?

cheers,

Robin
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Eyeroll1952
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Re: Plate solving decanters target

#9

Post by Eyeroll1952 »

This is getting curioser and curioser as Alice might say. May 12 I pointed to Arcturus but last night I told the mount to go to Vega, so the coordinate issue is even weirder. I don't specify coordinates, just command the mount by object, so whether Vega or Arcturus something is not right.

I need to look closer at where the mount thinks it is pointing... Once Vega and Arcturus are above the horizon the mount should tell me their coordinates.
Eyeroll1952
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Joined: Tue May 25, 2021 2:03 pm

Re: Plate solving decanters target

#10

Post by Eyeroll1952 »

This turned out to be substantially more complex than anticipated and I am still not 100% sure of what is going on. In case somebody else runs into similar issues this is what I ended up concluding/doing.

One bottom line appears to be that coordinates are not consistent between Wikipedia (J2000), Stellarium (J2000 or JNOW), and my EQ6 mount (JNOW). For three sample stars values are below. While Arcturus has far higher proper motion than the others the noted coordinate discrepancies appear much too high for proper motion to account for it. Whether the errors are due to different accounting for earth precession/nutation I can’t tell but there are folks out there suggesting it might be - https://astronomy.stackexchange.com/que ... stellarium . It then appears that I probably have to live with some centering errors in plate solving.

The unrelated issue of Stellarium veering off wildly was fixed with two steps. The first was to go into EQMOD and force synchronization of the mount encoders per https://www.cloudynights.com/topic/7488 ... -behavior/ . After doing that Stellarium was fine but the mount now had no idea where it was and pointed way off if I told it to go somewhere. In the end the fix was to go into the Synscan “Setup\Sync. Encoder” entry, tell the mount to go to a star, then use Stellarium to steer to the correct coordinates, and accept that pointing to synchronize the encoders, presumably from a Synscan perspective (rather than just Stellarium). This is all fairly confusing but in the end this appears to have fixed multiple issues…
Star coordinates.png
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