Exposure comparisons with CCD cameras


Roland Christen
 

Hello Astronuts,

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

https://www.astrobin.com/916uf7/B/

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:


Cheng-Yang Tan
 

Hi Rolando,
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

cytan

On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:


Hello Astronuts,

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

https://www.astrobin.com/916uf7/B/

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:


Roland Christen
 


 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.

I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.

Rolando


-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

cytan

On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:


Hello Astronuts,

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

https://www.astrobin.com/916uf7/B/

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:


Cheng-Yang Tan
 

Hi Rolando,
   
   I think you know more about this than I do. But here's what I think:

   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.

  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.

cytan



On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:



 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.

I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.

Rolando


-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

cytan

On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:


Hello Astronuts,

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

https://www.astrobin.com/916uf7/B/

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:


Roland Christen
 

My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.

Rolando



-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 1:09 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,
   
   I think you know more about this than I do. But here's what I think:

   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.

  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.

cytan



On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:



 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.

I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.

Rolando


-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

cytan

On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:


Hello Astronuts,

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

https://www.astrobin.com/916uf7/B/

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:


Stone, Jack G
 

Rolando – You give me hope! I will ping you later, I’ve been somewhat apprehensive for the past few years.

Finally the city replaced the MV with LED – guess what they must be 1million lumens – enough to bring daylight to my backyard.

Tips and tricks if you allow me to bug you.

 

Jack ~

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:22 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.

 

Rolando

 

 

 

-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 1:09 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,

   

   I think you know more about this than I do. But here's what I think:

 

   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.

 

  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.

 

cytan

 

 

 

On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:

 

 

 

 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.

 

I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.

 

Rolando

 

 

-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,

 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

 

cytan

 

On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:

 

 

Hello Astronuts,

 

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

 

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

 

 

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

 

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:

 


Roland Christen
 

Bring your questions up here in the user group. That's what we are for, not just for analyzing problems.

Rolando



-----Original Message-----
From: Stone, Jack G <jack.g.stone@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Jack Stone <mediwheel_js@...>
Sent: Tue, Aug 18, 2020 1:29 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Rolando – You give me hope! I will ping you later, I’ve been somewhat apprehensive for the past few years.
Finally the city replaced the MV with LED – guess what they must be 1million lumens – enough to bring daylight to my backyard.
Tips and tricks if you allow me to bug you.
 
Jack ~
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:22 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
 
My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.
 
Rolando
 
 
 
-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 1:09 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Hi Rolando,
   
   I think you know more about this than I do. But here's what I think:
 
   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.
 
  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.
 
cytan
 
 
 
On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:
 
 
 
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.
 
I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.
 
Rolando
 
 
-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Hi Rolando,
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
 
cytan
 
On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:
 
 
Hello Astronuts,
 
Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.
 
Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:
 
 
As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.
 
Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:
 


Stone, Jack G
 

Sorry – I did not mean that in a negative manner.

I’m just so impressed when someone has successfully tackled the LP challenge.

 

I worry that my questions would seem really dumb questions that I should know – hence my reluctance.

I did post a question regarding Observatory planning and available software.

But I never got a response

 

Story is that I purchased a spanking new AP1100 GTO4 – and the observatory I have seems like a very tight fit.  So a year later it sits unused.

So how can one make an assessment without models or ???  I tried simple geometry, but there is always something amiss in the 3D element.

Like the dome drive track and motor mount etc…..  The motor is rather ancient still works, and dialed in steady incremental rotations using my servo tester.

 

So now I’m thinking of selling the current one, but which one will fit, support my 14” Edge with HS etc… and not stand out like the statue of liberty.

Rather low profile as well.

Any thoughts or considerations would be welcomed.

As for the LED lights – Lenhance Extreme – but that would limit my targets – Any other thoughts?

 

I have tons of questions!!!

Also I’ve search on CN as well, and found a couple of others who restored their Boyd Observatories.

 

Cheers,

 

Jack ~

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:32 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

Bring your questions up here in the user group. That's what we are for, not just for analyzing problems.

 

Rolando

 

 

 

-----Original Message-----
From: Stone, Jack G <jack.g.stone@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Jack Stone <mediwheel_js@...>
Sent: Tue, Aug 18, 2020 1:29 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Rolando – You give me hope! I will ping you later, I’ve been somewhat apprehensive for the past few years.

Finally the city replaced the MV with LED – guess what they must be 1million lumens – enough to bring daylight to my backyard.

Tips and tricks if you allow me to bug you.

 

Jack ~

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:22 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.

 

Rolando

 

 

 

-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 1:09 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,

   

   I think you know more about this than I do. But here's what I think:

 

   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.

 

  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.

 

cytan

 

 

 

On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:

 

 

 

 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.

 

I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.

 

Rolando

 

 

-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,

 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

 

cytan

 

On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:

 

 

Hello Astronuts,

 

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

 

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

 

 

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

 

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:

 


Roland Christen
 

Your questions are always welcome in this group. They need to be specific so that people who have done something similar can comment.

When it comes to observatories, I only know roll-off roofs and their peculiarities. I have two of them now, one here in light pollution-city and one in a very dark site in Hawaii. We also have a remote observatory in Chile at 7000ft in the Andes mountains at Las Campanas. each one has their own issues and strengths, but with the right equipment, they can all do a super job.

As far as Domed observatories, I have only limited experience. They don't work for me because I like to be with my scope when imaging and most domes are too crowded. I also don't like the fact that the instruments (and observer) have to exit their stored heat out thru the dome slit, the same opening thru which the scope has to acquire images.

Rolando



-----Original Message-----
From: Stone, Jack G <jack.g.stone@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Stone, Jack G <jack.g.stone@...>
Sent: Tue, Aug 18, 2020 2:17 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Sorry – I did not mean that in a negative manner.
I’m just so impressed when someone has successfully tackled the LP challenge.
 
I worry that my questions would seem really dumb questions that I should know – hence my reluctance.
I did post a question regarding Observatory planning and available software.
But I never got a response
 
Story is that I purchased a spanking new AP1100 GTO4 – and the observatory I have seems like a very tight fit.  So a year later it sits unused.
So how can one make an assessment without models or ???  I tried simple geometry, but there is always something amiss in the 3D element.
Like the dome drive track and motor mount etc…..  The motor is rather ancient still works, and dialed in steady incremental rotations using my servo tester.
 
So now I’m thinking of selling the current one, but which one will fit, support my 14” Edge with HS etc… and not stand out like the statue of liberty.
Rather low profile as well.
Any thoughts or considerations would be welcomed.
As for the LED lights – Lenhance Extreme – but that would limit my targets – Any other thoughts?
 
I have tons of questions!!!
Also I’ve search on CN as well, and found a couple of others who restored their Boyd Observatories.
 
Cheers,
 
Jack ~
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:32 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
 
Bring your questions up here in the user group. That's what we are for, not just for analyzing problems.
 
Rolando
 
 
 
-----Original Message-----
From: Stone, Jack G <jack.g.stone@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Jack Stone <mediwheel_js@...>
Sent: Tue, Aug 18, 2020 1:29 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Rolando – You give me hope! I will ping you later, I’ve been somewhat apprehensive for the past few years.
Finally the city replaced the MV with LED – guess what they must be 1million lumens – enough to bring daylight to my backyard.
Tips and tricks if you allow me to bug you.
 
Jack ~
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:22 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
 
My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.
 
Rolando
 
 
 
-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 1:09 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Hi Rolando,
   
   I think you know more about this than I do. But here's what I think:
 
   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.
 
  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.
 
cytan
 
 
 
On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:
 
 
 
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.
 
I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.
 
Rolando
 
 
-----Original Message-----
From: Cheng-Yang Tan via groups.io <cytan299@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Hi Rolando,
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
 
cytan
 
On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:
 
 
Hello Astronuts,
 
Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.
 
Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:
 
 
As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.
 
Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:
 


Michael Hambrick <mike.hambrick@...>
 

Very good comparison Roland Thanks

I have read that the signal to noise ratio is higher for long exposures, but is there a limit to what can be accomplished with long exposures ? What happens to the stars and objects that reach the saturation limit ? Is it better to stack shorter, non-saturated exposures ?


Best Regards

Michael Hambrick
ARLANXEO
TSR Global Manufacturing Support
PO Box 2000
Orange, TX 77631-2000
Phone: +1 (409) 882-2799
email: mike.hambrick@...


 

Some of my experience with domes…

 

One way to offset the issue of heat in a domed observatory is to use an air conditioner during the day, set to the expected temperature at night. At night, the dome and air are already the same temp and the only real difference is humidity/dust in the air. This can be very expensive/impractical in colder climates like Illinois, but in some warmer locations it isn’t such a bad idea and can make for better images. In Texas this is how some people would handle the problem, and at the HET they keep the telescope freezing all winter to reduce the heat currents at night; the workers there all have to wear big coats all day even when inside.

 

Liam

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 14:28
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

Your questions are always welcome in this group. They need to be specific so that people who have done something similar can comment.

 

When it comes to observatories, I only know roll-off roofs and their peculiarities. I have two of them now, one here in light pollution-city and one in a very dark site in Hawaii. We also have a remote observatory in Chile at 7000ft in the Andes mountains at Las Campanas. each one has their own issues and strengths, but with the right equipment, they can all do a super job.

 

As far as Domed observatories, I have only limited experience. They don't work for me because I like to be with my scope when imaging and most domes are too crowded. I also don't like the fact that the instruments (and observer) have to exit their stored heat out thru the dome slit, the same opening thru which the scope has to acquire images.

 

Rolando

 

 

 

-----Original Message-----
From: Stone, Jack G <
jack.g.stone@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Stone, Jack G <
jack.g.stone@...>
Sent: Tue, Aug 18, 2020 2:17 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Sorry – I did not mean that in a negative manner.

I’m just so impressed when someone has successfully tackled the LP challenge.

 

I worry that my questions would seem really dumb questions that I should know – hence my reluctance.

I did post a question regarding Observatory planning and available software.

But I never got a response

 

Story is that I purchased a spanking new AP1100 GTO4 – and the observatory I have seems like a very tight fit.  So a year later it sits unused.

So how can one make an assessment without models or ???  I tried simple geometry, but there is always something amiss in the 3D element.

Like the dome drive track and motor mount etc…..  The motor is rather ancient still works, and dialed in steady incremental rotations using my servo tester.

 

So now I’m thinking of selling the current one, but which one will fit, support my 14” Edge with HS etc… and not stand out like the statue of liberty.

Rather low profile as well.

Any thoughts or considerations would be welcomed.

As for the LED lights – Lenhance Extreme – but that would limit my targets – Any other thoughts?

 

I have tons of questions!!!

Also I’ve search on CN as well, and found a couple of others who restored their Boyd Observatories.

 

Cheers,

 

Jack ~

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:32 AM
To:
main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

Bring your questions up here in the user group. That's what we are for, not just for analyzing problems.

 

Rolando

 

 

 

-----Original Message-----
From: Stone, Jack G <
jack.g.stone@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Jack Stone <
mediwheel_js@...>
Sent: Tue, Aug 18, 2020 1:29 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Rolando – You give me hope! I will ping you later, I’ve been somewhat apprehensive for the past few years.

Finally the city replaced the MV with LED – guess what they must be 1million lumens – enough to bring daylight to my backyard.

Tips and tricks if you allow me to bug you.

 

Jack ~

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:22 AM
To:
main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.

 

Rolando

 

 

 

-----Original Message-----
From: Cheng-Yang Tan via groups.io <
cytan299@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 1:09 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,

   

   I think you know more about this than I do. But here's what I think:

 

   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.

 

  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.

 

cytan

 

 

 

On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:

 

 

 

 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.

 

I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.

 

Rolando

 

 

-----Original Message-----
From: Cheng-Yang Tan via groups.io <
cytan299@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,

 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.

 

cytan

 

On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:

 

 

Hello Astronuts,

 

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

 

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:

 

 

As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.

 

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:

 


Daniel Borcard
 

Hi Rolando,

Sorry if I rarely chime in. I follow the group closely and am a happy owner of an AP1200 GTO and a Traveler.

Your comparison is very interesting, but rather extreme. In narrowband imaging with CCD cameras one rarely takes 1 minute subs, and few of us are enjoying plane- or satellite-less skies allowing 1 hour subs :-)

If you continue this experiment it would be interesting to also take intermediate-length subs: 6 x 10 minutes, 4 x 15 minutes or 3 x 20 minutes. These will likely be long enough for the signal to overcome the various sources of noise. I would actually be surprised if three 20 minute subs show less signal than an unique 60 minute exposure does.

With my AP Traveler and the AP Mach 1 I had at the time I used to go up to 30 minute subs, but I saw almost no improvement over 15 or 20 minutes. And I image through the worst of the light pollution dome of Montreal, Canada...

Clear skies!

Daniel


Hello Astronuts,

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:


As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding. 

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:
--------------------------------------------------------------------
Daniel Borcard
Observatoire du Geai Bleu
Les faits sont têtus. Les nier ne les fait pas disparaître.
--------------------------------------------------------------------





Cheng-Yang Tan
 

I don't know how useful this is, but there is a spreadsheet calculator to calculate optimum exposure given skyglow, ccd noise etc.

Optimum Exposures Calculator - Gibraltar Astronomical Society



I remember using this a long time ago, and the optimum exposure time at my location and my camera is between 5 to 10 min.

cytan



On Tuesday, August 18, 2020, 03:11:36 PM CDT, Michael Hambrick via groups.io <mike.hambrick@...> wrote:


Very good comparison Roland Thanks

I have read that the signal to noise ratio is higher for long exposures, but is there a limit to what can be accomplished with long exposures ? What happens to the stars and objects that reach the saturation limit ? Is it better to stack shorter, non-saturated exposures ?


Best Regards

Michael Hambrick
ARLANXEO
TSR Global Manufacturing Support
PO Box 2000
Orange, TX 77631-2000
Phone: +1 (409) 882-2799
email: mike.hambrick@...


Roland Christen
 


I have read that the signal to noise ratio is higher for long exposures, but is there a limit to what can be accomplished with long exposures ? What happens to the stars and objects that reach the saturation limit ? Is it better to stack shorter, non-saturated exposures ?
In the narrowband image all stars except the very faint ones are saturated when you process them the way i did. For LRGB I don't worry as much about stars as I do about the max level of my object (example a galaxy core0 not saturating. The stars will do what they want. I set my exposure for the object, not the stars.

Rolando


-----Original Message-----
From: Michael Hambrick via groups.io <mike.hambrick@...>
To: main@ap-gto.groups.io
Sent: Tue, Aug 18, 2020 3:11 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Very good comparison Roland Thanks

I have read that the signal to noise ratio is higher for long exposures, but is there a limit to what can be accomplished with long exposures ? What happens to the stars and objects that reach the saturation limit ? Is it better to stack shorter, non-saturated exposures ?


Best Regards

Michael Hambrick
ARLANXEO
TSR Global Manufacturing Support
PO Box 2000
Orange, TX 77631-2000
Phone: +1 (409) 882-2799
email: mike.hambrick@...


Roland Christen
 

A person inside a small amateur dome emits a lot of heat that escapes thru the dome slit. That ruins the image.

Rolando



-----Original Message-----
From: Liam Plybon <liam@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 3:17 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Some of my experience with domes…
 
One way to offset the issue of heat in a domed observatory is to use an air conditioner during the day, set to the expected temperature at night. At night, the dome and air are already the same temp and the only real difference is humidity/dust in the air. This can be very expensive/impractical in colder climates like Illinois, but in some warmer locations it isn’t such a bad idea and can make for better images. In Texas this is how some people would handle the problem, and at the HET they keep the telescope freezing all winter to reduce the heat currents at night; the workers there all have to wear big coats all day even when inside.
 
Liam
 
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 14:28
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
 
Your questions are always welcome in this group. They need to be specific so that people who have done something similar can comment.
 
When it comes to observatories, I only know roll-off roofs and their peculiarities. I have two of them now, one here in light pollution-city and one in a very dark site in Hawaii. We also have a remote observatory in Chile at 7000ft in the Andes mountains at Las Campanas. each one has their own issues and strengths, but with the right equipment, they can all do a super job.
 
As far as Domed observatories, I have only limited experience. They don't work for me because I like to be with my scope when imaging and most domes are too crowded. I also don't like the fact that the instruments (and observer) have to exit their stored heat out thru the dome slit, the same opening thru which the scope has to acquire images.
 
Rolando
 
 
 
-----Original Message-----
From: Stone, Jack G <
jack.g.stone@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Stone, Jack G <
jack.g.stone@...>
Sent: Tue, Aug 18, 2020 2:17 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Sorry – I did not mean that in a negative manner.
I’m just so impressed when someone has successfully tackled the LP challenge.
 
I worry that my questions would seem really dumb questions that I should know – hence my reluctance.
I did post a question regarding Observatory planning and available software.
But I never got a response
 
Story is that I purchased a spanking new AP1100 GTO4 – and the observatory I have seems like a very tight fit.  So a year later it sits unused.
So how can one make an assessment without models or ???  I tried simple geometry, but there is always something amiss in the 3D element.
Like the dome drive track and motor mount etc…..  The motor is rather ancient still works, and dialed in steady incremental rotations using my servo tester.
 
So now I’m thinking of selling the current one, but which one will fit, support my 14” Edge with HS etc… and not stand out like the statue of liberty.
Rather low profile as well.
Any thoughts or considerations would be welcomed.
As for the LED lights – Lenhance Extreme – but that would limit my targets – Any other thoughts?
 
I have tons of questions!!!
Also I’ve search on CN as well, and found a couple of others who restored their Boyd Observatories.
 
Cheers,
 
Jack ~
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:32 AM
To:
main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
 
Bring your questions up here in the user group. That's what we are for, not just for analyzing problems.
 
Rolando
 
 
 
-----Original Message-----
From: Stone, Jack G <
jack.g.stone@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Jack Stone <
mediwheel_js@...>
Sent: Tue, Aug 18, 2020 1:29 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Rolando – You give me hope! I will ping you later, I’ve been somewhat apprehensive for the past few years.
Finally the city replaced the MV with LED – guess what they must be 1million lumens – enough to bring daylight to my backyard.
Tips and tricks if you allow me to bug you.
 
Jack ~
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 11:22 AM
To:
main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
 
My "backyard' (AP observatory) is in a heavily light polluted area in an industrial park with large malls, gas stations, fast food joints etc, all competing for brightest lights in the neighborhood. The narrowband filter blocks a lot of that sky light, otherwise i would get a white frame with a luminance filter in a 1 hour exposure.
 
Rolando
 
 
 
-----Original Message-----
From: Cheng-Yang Tan via groups.io <
cytan299@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 1:09 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Hi Rolando,
   
   I think you know more about this than I do. But here's what I think:
 
   In order for stacking to actually show the faint details, it has to be a little above the noise floor and then stacking (or averaging) lowers the noise floor so that the coherent signal pops up. If there are no photons that were caught above the noise floor then averaging will do no good: zero == zero no matter how you average.
 
  That's why your long exposure caught enough photons above noise floor from the faint bits to show up. Your backyard must be much darker than mine, because as you increase the exposure time, noise also goes up as well, so at some point the noise is going to dominate  and increasing the exposure time doesn't buy you anything.
 
cytan
 
 
 
On Tuesday, August 18, 2020, 01:03:28 PM CDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:
 
 
 
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
Yes, higher read noise of course, but interestingly the amount of faint detail is also higher in the 1 hour exposure. Perhaps the detail is there in the stacked image, but buried in read noise.
 
I don't know how this would relate to CMOS cameras, but CCDs is a different animal. I'm going to try adding several 1 hour exposures if skies permit and see how much faint Ha I can dig out of my light polluted skies.
 
Rolando
 
 
-----Original Message-----
From: Cheng-Yang Tan via groups.io <
cytan299@...>
To:
main@ap-gto.groups.io <main@ap-gto.groups.io>; main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Tue, Aug 18, 2020 12:59 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras
Hi Rolando,
 This is a very interesting result. It looks like the noise of the exposure is dominated by the read noise in your CCD camera.
 
cytan
 
On Tuesday, August 18, 2020, 12:51:43 PM CDT, uncarollo2 <chris1011@...> wrote:
 
 
Hello Astronuts,
 
Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.
 
Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:
 
 
As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding.
 
Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:
 


Konstantin von Poschinger
 

Hi,

it belongs to. If you want to see the star color you need short exposures. If you want to see faint nebulas longer exposures are better.  You also always have to think of the background level. Near or in cities you will always take shorter exposures.

Konstantin



Am 18.08.2020 um 22:11 schrieb Michael Hambrick via groups.io <mike.hambrick@...>:

Very good comparison Roland Thanks

I have read that the signal to noise ratio is higher for long exposures, but is there a limit to what can be accomplished with long exposures ? What happens to the stars and objects that reach the saturation limit ? Is it better to stack shorter, non-saturated exposures ?


Best Regards

Michael Hambrick
ARLANXEO
TSR Global Manufacturing Support
PO Box 2000
Orange, TX 77631-2000
Phone: +1 (409) 882-2799
email: mike.hambrick@...


sbasprez
 

The lower background noise floor in the 60 minute image is easily explained mathematically.  Noise in a sum of stacked of images is increased by the square root of the number of subs stacked.  So summing the stack of 10 subs results in 3.16 time the noise of a single sub.  The signal on the other hand adds linearly.  So the signal in the summed stack is equal to the 60 minute exposure, but the noise floor in the stack is higher than the 60 minute single frame.


Roland Christen
 


Your comparison is very interesting, but rather extreme. In narrowband imaging with CCD cameras one rarely takes 1 minute subs,
I didn't take 1 min subs. I took 6 x 10 minute subs. Blush

Rolando


-----Original Message-----
From: Daniel Borcard <daniel.borcard@...>
To: main@ap-gto.groups.io
Sent: Tue, Aug 18, 2020 3:34 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Hi Rolando,

Sorry if I rarely chime in. I follow the group closely and am a happy owner of an AP1200 GTO and a Traveler.

Your comparison is very interesting, but rather extreme. In narrowband imaging with CCD cameras one rarely takes 1 minute subs, and few of us are enjoying plane- or satellite-less skies allowing 1 hour subs :-)

If you continue this experiment it would be interesting to also take intermediate-length subs: 6 x 10 minutes, 4 x 15 minutes or 3 x 20 minutes. These will likely be long enough for the signal to overcome the various sources of noise. I would actually be surprised if three 20 minute subs show less signal than an unique 60 minute exposure does.

With my AP Traveler and the AP Mach 1 I had at the time I used to go up to 30 minute subs, but I saw almost no improvement over 15 or 20 minutes. And I image through the worst of the light pollution dome of Montreal, Canada...

Clear skies!

Daniel


Hello Astronuts,

Last night was a good night to try some experiments with the Mach2 mount and my 160 EDF refractor. I have been shooting the Veil nebula for the last couple of nights, normally using 10 minute subs and stacking them. I have not been guiding, but using modeling of the path to get sharp round stars.

Last night i did one exposure of 60 minutes and 6 exposures of 10 minutes each (60 minute stack). I wanted to see how the faint detail and noise levels compare. It turns out that the single 60 minute shot has much lower noise and shows more fainter details than the 60 minute stacked image. In fact, it took 120 minutes of stacked images to equal the single 60 minute one. You can see the result here:


As noted, the images were stretched to bring up the faintest detail and to show the noise levels. It appears to me that longer exposures for narrowband produce better results faster. There are two drawbacks. The image can be ruined by satellites or airplane trails. A 1 hour exposure requires some guiding. 

Both images had the model running in the background, which was good for round stars in a 10 minute time interval. However for the 1 hour exposure I wanted to make sure the stars would be round and sharp, so I set up my Lodestar off-axis guider. The guider was set to take a 2 sec exposure every 10 seconds to nudge the two axes. The image below shows how well the mount guides when it is also being modeled:
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Daniel Borcard
Observatoire du Geai Bleu
Les faits sont têtus. Les nier ne les fait pas disparaître.
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Roland Christen
 

Aha, thank you for the explanation.

Rolando



-----Original Message-----
From: sbasprez via groups.io <beneckerus@...>
To: main@ap-gto.groups.io
Sent: Tue, Aug 18, 2020 3:52 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

The lower background noise floor in the 60 minute image is easily explained mathematically.  Noise in a sum of stacked of images is increased by the square root of the number of subs stacked.  So summing the stack of 10 subs results in 3.16 time the noise of a single sub.  The signal on the other hand adds linearly.  So the signal in the summed stack is equal to the 60 minute exposure, but the noise floor in the stack is higher than the 60 minute single frame.


Roland Christen
 


So summing the stack of 10 subs results in 3.16 time the noise of a single sub. 
Actually, the stack is not summed, rather it is Median combined. Don't know if that makes a difference. It allows stray hot pixels to be subtracted out in the final image.

Rolando


-----Original Message-----
From: uncarollo2 <chris1011@...> via groups.io <chris1011@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Tue, Aug 18, 2020 3:55 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Aha, thank you for the explanation.

Rolando



-----Original Message-----
From: sbasprez via groups.io <beneckerus@...>
To: main@ap-gto.groups.io
Sent: Tue, Aug 18, 2020 3:52 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

The lower background noise floor in the 60 minute image is easily explained mathematically.  Noise in a sum of stacked of images is increased by the square root of the number of subs stacked.  So summing the stack of 10 subs results in 3.16 time the noise of a single sub.  The signal on the other hand adds linearly.  So the signal in the summed stack is equal to the 60 minute exposure, but the noise floor in the stack is higher than the 60 minute single frame.