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to model or not to model

Brian Valente
 

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)
Howard Ritter
 

Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)
Brian Valente
 

My bad Howard, thanks for asking

length of exposure 300 sec
Is the model-disabled image a single exposure or an unregistered stack? Both are single exposures 
Over what period of time? They were completed one immediately after the other (after I realized what was happening, it was easy to grab the two for a side by side)


On Wed, Mar 15, 2023 at 10:10 PM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)




--

Samir Patel
 

Hi Brain,

How long does it take to do a 300 pt model? 

Virus-free.www.avg.com


On Thu, Mar 16, 2023 at 1:16 AM Brian Valente <bvalente@...> wrote:
My bad Howard, thanks for asking

length of exposure 300 sec
Is the model-disabled image a single exposure or an unregistered stack? Both are single exposures 
Over what period of time? They were completed one immediately after the other (after I realized what was happening, it was easy to grab the two for a side by side)

On Wed, Mar 15, 2023 at 10:10 PM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)




--

Brian Valente
 

>>>How long does it take to do a 300 pt model?

It can take 3-4 hours. Mainly because the camera i'm using (FLI Proline 16803) is incredibly slow to download, so it adds maybe 30-40 seconds for each frame

I should also mention 300 points is for the 20" telescope. A model that dense is not needed for the 80mm but it "gets the model for free" since it's sitting piggyback on the 20"

 


On Thu, Mar 16, 2023 at 7:15 AM Samir Patel <samir111275@...> wrote:
Hi Brain,

How long does it take to do a 300 pt model? 

Virus-free.www.avg.com

On Thu, Mar 16, 2023 at 1:16 AM Brian Valente <bvalente@...> wrote:
My bad Howard, thanks for asking

length of exposure 300 sec
Is the model-disabled image a single exposure or an unregistered stack? Both are single exposures 
Over what period of time? They were completed one immediately after the other (after I realized what was happening, it was easy to grab the two for a side by side)

On Wed, Mar 15, 2023 at 10:10 PM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)




--



--

Howard Ritter
 

Thanks, Brian. That’s really eye-opening. I’m looking forward to modeling my 1600ae once I get it off the tripod and onto a concrete pier.

But if I’m not mistaken, I’ve seen numerous unguided images posted here that show no trailing in similar lengths of exposure. Of course, these mounts may have been using a model too, but in any case, what’s the origin of your mount’s trailing? Is is imperfect PA? It looks too big to be due to atmospheric refraction.

I guess I’m assuming that modeling can compensate for imprecise PA, but this had never occurred to me before. I had thought that its primary benefit was to correct for refraction, but now that I think about it, it seems that correcting for imperfect PA might be its best use.

—howard

On Mar 16, 2023, at 1:16 AM, Brian Valente <bvalente@...> wrote:

My bad Howard, thanks for asking

length of exposure 300 sec
Is the model-disabled image a single exposure or an unregistered stack? Both are single exposures 
Over what period of time? They were completed one immediately after the other (after I realized what was happening, it was easy to grab the two for a side by side)

On Wed, Mar 15, 2023 at 10:10 PM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)






--

Jeffc
 

I’m kinda late to the thread.. but I’ll just add…

1/  I’m totally “mobile” (skies are not good at home; rarely do I setup here except for “testing”)

2/ If I do a full sky model , it is (iirc) “small”, I think 50 points. I run the model while doing something else like  eating dinner.  Also my understanding is the model doesn’t require full astronomical dark. 

3/ Mostly I use dec-arc model created by tha astrophysics-tools-plugin in NINA. Running the model is just another step of the image sequence script.  



On Mar 16, 2023, at 7:30 AM, Brian Valente <bvalente@...> wrote:


>>>How long does it take to do a 300 pt model?

It can take 3-4 hours. Mainly because the camera i'm using (FLI Proline 16803) is incredibly slow to download, so it adds maybe 30-40 seconds for each frame

I should also mention 300 points is for the 20" telescope. A model that dense is not needed for the 80mm but it "gets the model for free" since it's sitting piggyback on the 20"

 

On Thu, Mar 16, 2023 at 7:15 AM Samir Patel <samir111275@...> wrote:
Hi Brain,

How long does it take to do a 300 pt model? 

Virus-free.www.avg.com

On Thu, Mar 16, 2023 at 1:16 AM Brian Valente <bvalente@...> wrote:
My bad Howard, thanks for asking

length of exposure 300 sec
Is the model-disabled image a single exposure or an unregistered stack? Both are single exposures 
Over what period of time? They were completed one immediately after the other (after I realized what was happening, it was easy to grab the two for a side by side)

On Wed, Mar 15, 2023 at 10:10 PM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)




--



--

Brian Valente
 

Hi Howard

>>>what’s the origin of your mount’s trailing?

It's hard to say, i haven't had time to look closely at it, and it's remote so I can't go over and check it out. It's certainly possible it's a PA issue that has happened over time. (last pa was maybe 6 months ago)

However as I write this, I realize that's another benefit of sky modeling: It can account for whatever error there is even if I don't know the source of the error.

I'm headed down to visit the install soon, so I can report back


On Thu, Mar 16, 2023 at 7:45 AM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Thanks, Brian. That’s really eye-opening. I’m looking forward to modeling my 1600ae once I get it off the tripod and onto a concrete pier.

But if I’m not mistaken, I’ve seen numerous unguided images posted here that show no trailing in similar lengths of exposure. Of course, these mounts may have been using a model too, but in any case, what’s the origin of your mount’s trailing? Is is imperfect PA? It looks too big to be due to atmospheric refraction.

I guess I’m assuming that modeling can compensate for imprecise PA, but this had never occurred to me before. I had thought that its primary benefit was to correct for refraction, but now that I think about it, it seems that correcting for imperfect PA might be its best use.

—howard

On Mar 16, 2023, at 1:16 AM, Brian Valente <bvalente@...> wrote:

My bad Howard, thanks for asking

length of exposure 300 sec
Is the model-disabled image a single exposure or an unregistered stack? Both are single exposures 
Over what period of time? They were completed one immediately after the other (after I realized what was happening, it was easy to grab the two for a side by side)

On Wed, Mar 15, 2023 at 10:10 PM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)






--



--

Roland Christen
 


It looks too big to be due to atmospheric refraction.
Depending on where the scope is pointing, atmospheric refraction will produce anywhere from 10 to 150 arc seconds of trailing per hour. So it could be 1 to 15 arc seconds of movement in a 10 minute exposure. And that's with perfect polar alignment. The only place where the trailing would be zero with perfect PA is at the zenith.

Roland


-----Original Message-----
From: Howard Ritter via groups.io <howard.ritter@...>
To: main@ap-gto.groups.io
Sent: Thu, Mar 16, 2023 4:44 am
Subject: Re: [ap-gto] to model or not to model

Thanks, Brian. That’s really eye-opening. I’m looking forward to modeling my 1600ae once I get it off the tripod and onto a concrete pier.

But if I’m not mistaken, I’ve seen numerous unguided images posted here that show no trailing in similar lengths of exposure. Of course, these mounts may have been using a model too, but in any case, what’s the origin of your mount’s trailing? Is is imperfect PA? It looks too big to be due to atmospheric refraction.

I guess I’m assuming that modeling can compensate for imprecise PA, but this had never occurred to me before. I had thought that its primary benefit was to correct for refraction, but now that I think about it, it seems that correcting for imperfect PA might be its best use.

—howard

On Mar 16, 2023, at 1:16 AM, Brian Valente <bvalente@...> wrote:

My bad Howard, thanks for asking

length of exposure 300 sec
Is the model-disabled image a single exposure or an unregistered stack? Both are single exposures 
Over what period of time? They were completed one immediately after the other (after I realized what was happening, it was easy to grab the two for a side by side)

On Wed, Mar 15, 2023 at 10:10 PM Howard Ritter via groups.io <howard.ritter=mac.com@groups.io> wrote:
Hi, Brian—

That’s pretty impressive evidence! More information would be helpful, specifically the length of exposure or integration. Is the model-disabled image a single exposure or an unregistered stack? Over what period of time?

—howard

On Mar 15, 2023, at 10:03 PM, Brian Valente <bvalente@...> wrote:

Hi everyone

I experienced an unscheduled imaging comparison between tracking with sky modeling enabled, and tracking with sky modeling disabled.

I am running my unguided widefield 80mm refractor with ASI6200mc (approx 480mm focal length, 1.6"/pix) on the AP1600ae and I noticed some star elongation. I logged on to the telescope and sure enough, tracking corrections were disabled. I enabled them and made sure to select dec arc tracking, and the difference is quite noticeable

Here's a comparison screen shot crop @600%. The only difference is that sky modeling is enabled (I use approx 300 pt sky model: the 80mm sits atop the CDK20)






--


--
Roland Christen
Astro-Physics
Andrew Arai
 

On Thu, Mar 16, 2023 at 07:52 AM, Brian Valente wrote:
It's hard to say, i haven't had time to look closely at it, and it's remote so I can't go over and check it out. It's certainly possible it's a PA issue that has happened over time. (last pa was maybe 6 months ago)
 
However as I write this, I realize that's another benefit of sky modeling: It can account for whatever error there is even if I don't know the source of the error.
 
I'm headed down to visit the install soon, so I can report back
Brian,

Couldn't you just run the NINA polar alignment procedure without actually making any mechanical corrections to check your current polar alignment?

Andrew
Roland Christen
 

Polar alignment does not negate the atmospheric refraction produced tracking error which can be quite large when imaging away from the zenith.

Roland

-----Original Message-----
From: Andrew Arai <andrewarai@...>
To: main@ap-gto.groups.io
Sent: Thu, Mar 16, 2023 10:28 am
Subject: Re: [ap-gto] to model or not to model

On Thu, Mar 16, 2023 at 07:52 AM, Brian Valente wrote:
It's hard to say, i haven't had time to look closely at it, and it's remote so I can't go over and check it out. It's certainly possible it's a PA issue that has happened over time. (last pa was maybe 6 months ago)
 
However as I write this, I realize that's another benefit of sky modeling: It can account for whatever error there is even if I don't know the source of the error.
 
I'm headed down to visit the install soon, so I can report back
Brian,

Couldn't you just run the NINA polar alignment procedure without actually making any mechanical corrections to check your current polar alignment?

Andrew

--
Roland Christen
Astro-Physics
Dean Jacobsen
 

It has been my practice over the years to try and image an object only when higher than 45 degrees to limit the effect of atmospheric refraction.  It this a sound practice or should I wait until the object is higher in the sky where possible?  I have been imaging unguided with my Mach2 using the APCC/APPM software for almost 3 years now at focal lengths varying from 380mm to 1000mm with no sign of any problems.
--
Dean Jacobsen
Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/

Roland Christen
 

Even at 45 degrees you will nee a model to correct for atmospheric refraction drift. It is not zero until you get to the zenith. Plus there may be objects that start at 20 degrees and never rise above 30 degrees at the meridian. Objects in the south like Omega Centauri.

Roland

-----Original Message-----
From: Dean Jacobsen <deanjacobsen@...>
To: main@ap-gto.groups.io
Sent: Thu, Mar 16, 2023 12:10 pm
Subject: Re: [ap-gto] to model or not to model

It has been my practice over the years to try and image an object only when higher than 45 degrees to limit the effect of atmospheric refraction.  It this a sound practice or should I wait until the object is higher in the sky where possible?  I have been imaging unguided with my Mach2 using the APCC/APPM software for almost 3 years now at focal lengths varying from 380mm to 1000mm with no sign of any problems.
--
Dean Jacobsen
Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/

--
Roland Christen
Astro-Physics
Brian Valente
 

Dean I'm like you: i aim for 45-50 degrees minimum. Some of the best imagers I know only image +/- 2 HA from the meridian.



On Thu, Mar 16, 2023 at 3:10 PM Dean Jacobsen <deanjacobsen@...> wrote:
It has been my practice over the years to try and image an object only when higher than 45 degrees to limit the effect of atmospheric refraction.  It this a sound practice or should I wait until the object is higher in the sky where possible?  I have been imaging unguided with my Mach2 using the APCC/APPM software for almost 3 years now at focal lengths varying from 380mm to 1000mm with no sign of any problems.
--
Dean Jacobsen
Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/



--

Brian Valente
 

>>>Couldn't you just run the NINA polar alignment procedure without actually making any mechanical corrections to check your current polar alignment?

I could check PA any number of ways, but I don't have to ;)

I'm headed down there anyways so time to re-up on polar alignment

On Thu, Mar 16, 2023 at 1:28 PM Andrew Arai <andrewarai@...> wrote:
On Thu, Mar 16, 2023 at 07:52 AM, Brian Valente wrote:
It's hard to say, i haven't had time to look closely at it, and it's remote so I can't go over and check it out. It's certainly possible it's a PA issue that has happened over time. (last pa was maybe 6 months ago)
 
However as I write this, I realize that's another benefit of sky modeling: It can account for whatever error there is even if I don't know the source of the error.
 
I'm headed down to visit the install soon, so I can report back
Brian,

Couldn't you just run the NINA polar alignment procedure without actually making any mechanical corrections to check your current polar alignment?

Andrew



--

Mike Sandy
 

Hi Brian,

I finally finished the set up of my new Mach 2 (thanks to your help getting over my issue).  I ran a small model (150 points) that night and continued my set up.  Today I had a rare clear night and was able to successfully test a complete image sequence in NINA including a meridian flip - I’m ready for some more clear skies!  After my test, I took a 300 sec test exposure unguided with the small model.  The results were okay, but there was a small amount of trails (much less than your image without the model on) when you blew the image up.  So I ran a new 300 point model - took about 1.75 hours.  The result was very satisfying.  Not detectable trailing, nice tight stars with a 300 sec exposure at 910mm focal length.  I suspect it could go longer.  I couldn’t be happier with that mount - simply beautiful in form and function!

Mike
Brian Valente
 

Great job Mike that all sounds great



On Fri, Mar 17, 2023 at 12:19 AM Mike Sandy <mike@...> wrote:
Hi Brian,

I finally finished the set up of my new Mach 2 (thanks to your help getting over my issue).  I ran a small model (150 points) that night and continued my set up.  Today I had a rare clear night and was able to successfully test a complete image sequence in NINA including a meridian flip - I’m ready for some more clear skies!  After my test, I took a 300 sec test exposure unguided with the small model.  The results were okay, but there was a small amount of trails (much less than your image without the model on) when you blew the image up.  So I ran a new 300 point model - took about 1.75 hours.  The result was very satisfying.  Not detectable trailing, nice tight stars with a 300 sec exposure at 910mm focal length.  I suspect it could go longer.  I couldn’t be happier with that mount - simply beautiful in form and function!

Mike



--

bob
 

Hi Brian,

Weather has kept me from using my new AE mount, so I haven't been able to do any modeling yet. I'm curious about the download time of 30 to 40 seconds, I also use the FLI PL16803
and my downloads only take maybe 5 or 6 seconds 1x1 if I'm not running the RBI. Is this your normal download time.  
Brian Valente
 

Hi Bob

Thanks for sharing that. Our Proline 16803 definitely has had faster days. We are attempting to diagnose the cause and try to remedy it (i type to you from the airport lounge.) 

I have heard vague internet lore regarding reinstalling drivers, etc. so we will try our hand

If you have any suggestions, i’m all ears

Brian


On Fri, Mar 17, 2023 at 3:02 PM bob <skybob727@...> wrote:
Hi Brian,

Weather has kept me from using my new AE mount, so I haven't been able to do any modeling yet. I'm curious about the download time of 30 to 40 seconds, I also use the FLI PL16803
and my downloads only take maybe 5 or 6 seconds 1x1 if I'm not running the RBI. Is this your normal download time.  

--

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