Plate Solve in Sequence Loop

Questions, tips, information and discussions about using the SharpCap Sequencer and Sequence Planner tools
rac19
Posts: 142
Joined: Wed Apr 21, 2021 2:01 pm

Plate Solve in Sequence Loop

#1

Post by rac19 »

If I have a sequence loop that captures 2O images then performs a plate solve and resynch and loops around for the next set of images, the target (galaxy etc) is not centred at the start of each 20 image capture session.

If I do the same thing manually, the target is centred at the commencement of each 20 image capture. It's as though, in a sequence, the coordinates of the original target are not accurately maintained,
rac19
Posts: 142
Joined: Wed Apr 21, 2021 2:01 pm

Re: Plate Solve in Sequence Loop

#2

Post by rac19 »

To explain further.

My goal is to reduce long term drift on the RA axis over an hour or two. If I manually stop image capture, say every 10 minutes, plate solve and synch, then resume image capture, it seems to work. There is still some drift, but only 10 minutes worth. If I automate this process in a Sharpcap sequence, the long term drift still occurs.
zerolatitude
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Re: Plate Solve in Sequence Loop

#3

Post by zerolatitude »

Thats odd.

Used to work fine for me earlier - dont use it much since I started guiding.

I don't think there has been change to the functionality.

Can you post the sequence code?
rac19
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Joined: Wed Apr 21, 2021 2:01 pm

Re: Plate Solve in Sequence Loop

#4

Post by rac19 »

I really expected it to work, it seems so simple. I am connecting via CPWI and I noticed , on the CPWI beta forum last night, that they are investigating a possible issue with the way that synch is handled via ASCOM. It has something to do with not actually adding a reference to the alignment model.

I can't see how that would make the "plate solve and sync" button on the Sharpcap telescope control panel work differently to a "plate solve and sync" command from the sequencer, but perhaps they make slightly different calls to CPWI. I will send the script when I get a chance but it is very basic.
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admin
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Re: Plate Solve in Sequence Loop

#5

Post by admin »

Hi,

can you check your plate solving settings? If you are using the option to 'sync and re goto target' then it all should work fine. If you are using the 'offset goto to center target' option then it may not work, since after the first plate solve operation the co-ordinates move to something slightly different (that should put the target in the center again). If it is that then I had better think about doing something about it (it's been something I've been aware of as a glitch for some time, but until now it had not affected anyone in real life).

cheers,

Robin
rac19
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Re: Plate Solve in Sequence Loop

#6

Post by rac19 »

Hi Robin,

The choice are "Sync mount and re-centre target" (which is the current selection) and "Offset the mount position to centre the target", also "Do nothing" of course".

Last night, I set up for 8 sets of 60 subs (10 seconds per sub) with a plate solve and sync between each set. Attached the first subs in each set after plate solve and sync (and a 120 second delay) sync. It looks to more a random than drifting a offset, which is better than an accumulated drift, but I usually dose the target dead centre every time when I click the plate solve and sync button in the telescope control panel. The stacked image (480 subs) was actually quick good, it just needed a bit of cropping.
Attachments
D35A7F52-B773-478F-87DE-3570DA650D8D.jpeg
D35A7F52-B773-478F-87DE-3570DA650D8D.jpeg (724.72 KiB) Viewed 1971 times
4E67A35B-084A-47C1-B473-D7D42F8CFBD5.jpeg
4E67A35B-084A-47C1-B473-D7D42F8CFBD5.jpeg (723.59 KiB) Viewed 1971 times
3F1EA6FF-14A9-4007-8821-ED57E9023352.jpeg
3F1EA6FF-14A9-4007-8821-ED57E9023352.jpeg (724.04 KiB) Viewed 1971 times
7819B5B1-DEFB-4BB9-880C-EC434F8CBFEA.jpeg
7819B5B1-DEFB-4BB9-880C-EC434F8CBFEA.jpeg (724.44 KiB) Viewed 1971 times
A4120854-59D7-49BD-BB3E-815DAD5740C5.jpeg
A4120854-59D7-49BD-BB3E-815DAD5740C5.jpeg (724.8 KiB) Viewed 1971 times
D8ED7609-664A-4EF3-BBDC-8484EB12EA5F.jpeg
D8ED7609-664A-4EF3-BBDC-8484EB12EA5F.jpeg (724.08 KiB) Viewed 1971 times
1AC75205-6438-4F0A-B6E5-4DCE99BF964F.jpeg
1AC75205-6438-4F0A-B6E5-4DCE99BF964F.jpeg (723.16 KiB) Viewed 1971 times
Last edited by rac19 on Fri Jun 10, 2022 4:34 am, edited 2 times in total.
rac19
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Re: Plate Solve in Sequence Loop

#7

Post by rac19 »

The last sub + final image.
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194AC292-4402-4FAC-84C4-5AD4DFA36378.jpeg
194AC292-4402-4FAC-84C4-5AD4DFA36378.jpeg (120.35 KiB) Viewed 1970 times
AB975BDB-BBC4-48FA-B479-5FCBA3FBB371.jpeg
AB975BDB-BBC4-48FA-B479-5FCBA3FBB371.jpeg (724.69 KiB) Viewed 1970 times
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Re: Plate Solve in Sequence Loop

#8

Post by admin »

Hi,

OK, so all your SharpCap settings sound as though they are correct. Now I'm starting to wonder if there is some sort of backlash or random variation in your mount movements... Each recenter is accomplished by a GOTO movement, and depending on the size and direction of any accumulated drift, that could give slight offsets if you have any backlash in the mount gearing.

One interesting experiment to check this would be to move the mount away from the target in different directions a few times and then make a GOTO back to the same co-ordinates. If the image after the GOTO is consistent then the mount is doing a good job in getting back to the same place and this is unlikely to be the explanation we are looking for. If the image is a little off each time in a similar way to the images above then we have tracked down the problem.

cheers,

Robin
rac19
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Re: Plate Solve in Sequence Loop

#9

Post by rac19 »

I have always been impressed that, regardless of the considerable gear play in the Evolution mount, if I wait for everything to settle following a GoTo before initiating a plate solve and re-centre from the telescope control panel, the target ends up dead centre in the frame. Even if there is drift after the GoTo, the target appears to be off centre at first, then drifts to be precisely centred. This is the reason for the 2 minute dealt before recommencing image capture.

Is it possible that sequence call (unintentionally) ignores the Plate Solve setting and operates in "Offset the mount position to centre the target" mode all the time? Unlikely perhaps, but such things can happen.
rac19
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Re: Plate Solve in Sequence Loop

#10

Post by rac19 »

Some further thoughts.

There can be some very visible drift after a GoTo as any slack in the gear train is taken up and plate solve & re-sync actually takes this into account as part of the error calculation.

With the sequencer, the aim is to correct for a much slower (imperceptible) drift that occurs over the ensuing 10 minutes. I guess that this additional drift will also be part of the error calculation, which complicates things.
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