Date   

Re: #APCC - V1.9 Tracking Error #APCC

Craig Young
 

One thing to try is to configure your main camera as a guider, but do not make guiding corrections.  Then center on a bright star and make a graph of your tracking over say ten minutes.  This will show you if you have backlash and also the direction and magnitude of drift in both axis.  This data can then be used to accurately measure subsequent changes made to the mount/camera orientation and tracking methodology.

Craig


Re: #APCC - V1.9 Tracking Error #APCC

Ray Gralak
 

That screenshot shows there is considerably more randomness in declination.

There is a difference in tube flexure from one side to the other, which implies *something* might be moving. There is also a lot of cantilever flexure, but it is reasonably consistent on both sides of the pier.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Rouz
Sent: Friday, August 20, 2021 1:59 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

Model values


Re: #APCC - V1.9 Tracking Error #APCC

Roland Christen
 

By any chance, are you trying to create a model using a separate guide scope rather than with the main instrument?

Roland



-----Original Message-----
From: Rouz <rbidshahri@...>
To: main@ap-gto.groups.io
Sent: Fri, Aug 20, 2021 4:05 pm
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

Roland,

One concern I have is that the image drifted in pretty much the same direction previously when I tried with a small refractor as a guider with PHD but without APCC.

I figured either the refractor was flexing or my polar alignment of off so decided on going unguided with APCC.

Previous OAG guiding was spot on but with the addition of a reducer I no longer have the space.

--
Roland Christen
Astro-Physics


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 
Edited

Hi Dominique,

I believe its moving West to East.

Rouz


Re: #APCC - V1.9 Tracking Error #APCC

Roland Christen
 

That's a different kettle of fish - a red herring for sure. You cannot guide an RC with a separate guide scope and achieve any kind of accuracy. The two scopes will not track in the same direction at the arc sec level.

Roland

-----Original Message-----
From: Rouz <rbidshahri@...>
To: main@ap-gto.groups.io
Sent: Fri, Aug 20, 2021 4:05 pm
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

Roland,

One concern I have is that the image drifted in pretty much the same direction previously when I tried with a small refractor as a guider with PHD but without APCC.

I figured either the refractor was flexing or my polar alignment of off so decided on going unguided with APCC.

Previous OAG guiding was spot on but with the addition of a reducer I no longer have the space.

--
Roland Christen
Astro-Physics


Re: #APCC - V1.9 Tracking Error #APCC

Dominique
 

Hi,
The case appeals to me and to see the small video the drift of the crescent seems clearly East-West, then?

Dominique


Re: #APCC - V1.9 Tracking Error #APCC

Ray Gralak
 

Rouz,

I didn't say it was flexure, but everything bends to some extent. It is simple physics.

My point was that any flexure will be modeled with a simplified calculation that represents a perfectly solid object made of the same material. Under most cases, that is good enough. However, scopes with mirrors can produce a deviation that can be enough to cause calculation errors.

Again, I haven't concluded this is what is happening in your setup. It is just a possibility.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Rouz
Sent: Friday, August 20, 2021 1:49 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

Ray,

I had it pointing at zenith (85 degrees) so having the mirror almost flat on the cell and the focuser hanging
downwards.
Tightened each and every bolt in the setup too.

The mirror is bonded to the cell.
The focuser capacity is 25 lbs I have 8 lbs on it.

I doubt its flex as well.


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 

Roland,

One concern I have is that the image drifted in pretty much the same direction previously when I tried with a small refractor as a guider with PHD but without APCC.

I figured either the refractor was flexing or my polar alignment of off so decided on going unguided with APCC.

Previous OAG guiding was spot on but with the addition of a reducer I no longer have the space.


Re: #APCC - V1.9 Tracking Error #APCC

Roland Christen
 

I don't know what "down" is. So I will have to guess.

When doing unguided imaging with modeling, it's not just the RA axis that has to track accurately. Dec has to also track, although at a much slower rate than RA. Since you have a non-encoder mount, the Dec axis will have some errors. Most of them are handled by the model, but one in particular cannot be compensated for by any model. And that error is Dec backlash. All non-encoder mounts have Dec backlash, and it can amount to anywhere from 5 to 25 arc seconds. It can even be random, depending on where you are pointing in the sky.

This means that when you plot data points along an hour angle, rather than along a constant Dec arc, your Dec axis swings back and forth and introduces + or - backlash errors to each data point. RA is not affected since it moves continually in one direction and never reverses. So, once you have a model built with those points, trying to synthesize a constant Dec arc is not going to be accurate. If, however, you build a model along constant Dec arcs, the Dec axis will be perfectly stationary and backlash errors are no longer introduced into the data.

For those who have encoder mounts, the above limitations do not apply because Dec backlash is essentially zero with any of our dual axis encoder mounts.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Rouz <rbidshahri@...>
To: main@ap-gto.groups.io
Sent: Fri, Aug 20, 2021 3:45 pm
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

Roland,

I'm not entirely sure.
The target moves "down" mostly with a 90 degree camera angle. 

I have solved the 1st and last image of the session.



First image
Observation start time ... 2021-08-20 09:16:09 UTC
Image center ............. RA: 20 11 56.941 Dec: +38 22 33.21

Last image:
Observation start time ... 2021-08-20 10:07:53 UTC
Image center ............. RA: 20 11 58.590 Dec: +38 22 21.79

--
Roland Christen
Astro-Physics


Re: #APCC - V1.9 Tracking Error #APCC

Bill Long
 

Oh yeah I don't think PE is related, just something to add to the checklist when prepping a system for unguided.

If the drift is in declination then yeah PA could be related.


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Rouz <rbidshahri@...>
Sent: Friday, August 20, 2021 1:52 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error
 
Bill,

Yes unguided with APCC corrections.

I doubt its PE as the image is consistently drifting in 1 direction. PE would cycle (sine wave like) around a certain point I believe.

It is neutral fine balanced as well.

I'm not sure about the polar alignment though. Could that be a cause?

Rouz,


 


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 

Model values


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 

Bill,

Yes unguided with APCC corrections.

I doubt its PE as the image is consistently drifting in 1 direction. PE would cycle (sine wave like) around a certain point I believe.

It is neutral fine balanced as well.

I'm not sure about the polar alignment though. Could that be a cause?

Rouz,


 


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 

Ray,

I had it pointing at zenith (85 degrees) so having the mirror almost flat on the cell and the focuser hanging downwards.
Tightened each and every bolt in the setup too.

The mirror is bonded to the cell.
The focuser capacity is 25 lbs I have 8 lbs on it.

I doubt its flex as well.


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 

Roland,

I'm not entirely sure.
The target moves "down" mostly with a 90 degree camera angle. 

I have solved the 1st and last image of the session.



First image
Observation start time ... 2021-08-20 09:16:09 UTC
Image center ............. RA: 20 11 56.941 Dec: +38 22 33.21

Last image:
Observation start time ... 2021-08-20 10:07:53 UTC
Image center ............. RA: 20 11 58.590 Dec: +38 22 21.79


Re: #APCC - V1.9 Tracking Error #APCC

Bill Long
 

This is unguided imaging right? If so as a best practice I dial in my PA as close as I can with SharpCap before I build the model. When I was not using encoders I would ensure my PEC curve was solid (~1" or less) using PEMPro and build a new curve if it was no longer correcting as well. Also switch your balancing to neutral in both axis of you haven't already.

Not saying any of these are the cause, just some things to do if you're trying to image unguided.


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Rouz <rbidshahri@...>
Sent: Friday, August 20, 2021 1:22 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error
 
Also, I suspect polar alignment isn't perfect. Could that be the cause.

The model can correct for that right? To what degree.

Is that polar az and polar Alt values in the model?


Re: #APCC - V1.9 Tracking Error #APCC

Roland Christen
 

It's not a flex problem, Ray.

Roland



-----Original Message-----
From: Ray Gralak <iogroups@...>
To: main@ap-gto.groups.io
Sent: Fri, Aug 20, 2021 3:31 pm
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

> I believe its not a flex problem as its very consistent.

It's good that it is consistent, but it is possible that it is unmodeled flexure. The pointing terms best model a solid object with consistent flexure characteristics. When you have a large mirror on one end of the scope the flexure can be uneven as a whole across the scope.

That's what the dec-arc tracking is supposed to handle but the path that the hour-angle point creation strategy takes can introduce random flexures that are not there when doing a declination arc.

-Ray

> -----Original Message-----
> From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Rouz
> Sent: Friday, August 20, 2021 1:08 PM
> To: main@ap-gto.groups.io
> Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error
>
> Here is another blink clip of the previous nights tracking with a model with less points.
>
> I believe its not a flex problem as its very consistent.
>
>
> https://www.dropbox.com/s/ke6l2foort7jpod/tracking%2018-Aug-21.wmv?dl=0
>
>







--
Roland Christen
Astro-Physics


Re: #APCC - V1.9 Tracking Error #APCC

Ray Gralak
 

I believe its not a flex problem as its very consistent.
It's good that it is consistent, but it is possible that it is unmodeled flexure. The pointing terms best model a solid object with consistent flexure characteristics. When you have a large mirror on one end of the scope the flexure can be uneven as a whole across the scope.

That's what the dec-arc tracking is supposed to handle but the path that the hour-angle point creation strategy takes can introduce random flexures that are not there when doing a declination arc.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Rouz
Sent: Friday, August 20, 2021 1:08 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

Here is another blink clip of the previous nights tracking with a model with less points.

I believe its not a flex problem as its very consistent.


https://www.dropbox.com/s/ke6l2foort7jpod/tracking%2018-Aug-21.wmv?dl=0


Re: #APCC - V1.9 Tracking Error #APCC

Roland Christen
 

If you can answer my question I could probably tell you what's happening.

Roland



-----Original Message-----
From: Rouz <rbidshahri@...>
To: main@ap-gto.groups.io
Sent: Fri, Aug 20, 2021 3:22 pm
Subject: Re: [ap-gto] #APCC - V1.9 Tracking Error

Also, I suspect polar alignment isn't perfect. Could that be the cause.

The model can correct for that right? To what degree.

Is that polar az and polar Alt values in the model?

--
Roland Christen
Astro-Physics


Re: #APCC - V1.9 Tracking Error #APCC

Rouz
 

Also, I suspect polar alignment isn't perfect. Could that be the cause.

The model can correct for that right? To what degree.

Is that polar az and polar Alt values in the model?

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