Date   

Re: Small Dome Amateur Observatories - Downsides

Stone, Jack G
 

Dale,

Thank you - yes living near the bay I do get wind in the afternoon.
I forgot about that.

Jack ~

-----Original Message-----
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Dale Ghent
Sent: Tuesday, August 18, 2020 2:24 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Small Dome Amateur Observatories - Downsides


Another nice aspect of RoRs is that they can be arbitrarily sized and made to accommodate multiple, independently pointing imaging setups. So if you have your permanent setup on a pier that's cemented to the ground, you can design the bay so that's off to one side and leaves enough open floor to put a portable setup. Or another pier. Whatever your heart desires.

I would not worry about stray light. IF that is an issue, you can address it with some pop-up panels on the perimeter walls. The only real thing that a dome wins out on is wind shielding, which can also be mitigated somewhat on a RoR.

On Aug 18, 2020, at 5:14 PM, Liam Plybon <liam@astro-physics.com> wrote:

Don’t get me wrong; a roll off observatory is much better for imaging when possible. You can’t fully eliminate the heat issue on a dome no matter how hard you try because domes funnel heat past the aperture. My point is that there are some ways to partially mitigate the issue. Slatted domes are another method I have seen, but you would still be better off just removing the roof entirely.



Liam



From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Stone, Jack G
Sent: Tuesday, August 18, 2020 16:04
To: main@ap-gto.groups.io
Cc: Stone, Jack G <jack.g.stone@intel.com>
Subject: [ap-gto] Small Dome Amateur Observatories - Downsides



Renamed Subject:



Liam – Rolando has a point.

I have noticed that after time – the heat convection from my body does warm up the dome.

Most time I left the door open, but still heat rises.



Rolando – The dome just looked kool according to my wife. Footprint for a roll-off will require presidential approval.

So other option is a flip top roof.

The other aspect is that it kept the stray light off from the sides – I’ve attached some images for reference.



Thanks,



Jack ~



From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@aol.com> via groups.io
Sent: Tuesday, August 18, 2020 1:47 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras



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@astro-physics.com>
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@aol.com> 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@intel.com>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Stone, Jack G <jack.g.stone@intel.com>
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@aol.com> 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@intel.com>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Jack Stone <mediwheel_js@sbcglobal.net>
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@aol.com> 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=yahoo.com@groups.io>
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@aol.com> via groups.io <chris1011=aol.com@groups.io> 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=yahoo.com@groups.io>
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@aol.com> 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:



<image001.png>


Re: Exposure comparisons with CCD cameras

sbasprez
 

Median combination is a form of averaging where the median value of each pixel in the stack is assigned to the output value whereas a plain average is just the sum of the values divided by the number of subs stacked.  If there were no noise, the median and the average would be the same.  In any event, they will be very close to each other in a well operating system.

In the analysis in my initial reply I used summation instead of average because the signal level in an average is 1/10th that of the 60 minute frame.  You have to either compare the sum of the subs with the 60 minute frame directly, or you have to compare the average or median result with the 60 minute frame divided by 10.  The signal to noise ratio in either comparison is the same.  Averaging is done so that the result does not exceed the maximum 65,535 value in 16 bit calculations.  If you were doing floating point calculations, summation would not overflow.

One additional thought on why more faint detail is visible in the 60 minute exposure.  Let's view this in terms of an average of the stack vs. the 60 minute frame.  In the 10 minute subs the faintest details are barely above the read noise and 1/10th the value of those details in the 60 minute frame.  Now, as stated above, to compare the averaged stack to the 60 minute frame we need to divide it by 10.  The read  noise in the 60 minute frame is divided by 10 as well, so it is effectively one tenth the noise of single sub frame and 1/3.16 (0.316 times) of the averaged stack.  So if you just consider the small dynamic range between the noise floor and the signal value of the faint details, the signal to noise ratio is considerably greater in the 60 minute frame and they can be seen.


Re: Exposure comparisons with CCD cameras

Cheng-Yang Tan
 


I stack using average in Nebulosity and the noise floor reduction is 1/sqrt(n), where n is the number of subframes. So having more subs will reduce the noise floor. But if the photons aren’t above the noise floor to begin with, averaging doesn’t help.

On Tuesday, August 18, 2020, 3:52 PM, sbasprez via groups.io <beneckerus@...> wrote:

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.


Re: Small Dome Amateur Observatories - Downsides

Dale Ghent
 

Another nice aspect of RoRs is that they can be arbitrarily sized and made to accommodate multiple, independently pointing imaging setups. So if you have your permanent setup on a pier that's cemented to the ground, you can design the bay so that's off to one side and leaves enough open floor to put a portable setup. Or another pier. Whatever your heart desires.

I would not worry about stray light. IF that is an issue, you can address it with some pop-up panels on the perimeter walls. The only real thing that a dome wins out on is wind shielding, which can also be mitigated somewhat on a RoR.

On Aug 18, 2020, at 5:14 PM, Liam Plybon <liam@astro-physics.com> wrote:

Don’t get me wrong; a roll off observatory is much better for imaging when possible. You can’t fully eliminate the heat issue on a dome no matter how hard you try because domes funnel heat past the aperture. My point is that there are some ways to partially mitigate the issue. Slatted domes are another method I have seen, but you would still be better off just removing the roof entirely.



Liam



From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Stone, Jack G
Sent: Tuesday, August 18, 2020 16:04
To: main@ap-gto.groups.io
Cc: Stone, Jack G <jack.g.stone@intel.com>
Subject: [ap-gto] Small Dome Amateur Observatories - Downsides



Renamed Subject:



Liam – Rolando has a point.

I have noticed that after time – the heat convection from my body does warm up the dome.

Most time I left the door open, but still heat rises.



Rolando – The dome just looked kool according to my wife. Footprint for a roll-off will require presidential approval.

So other option is a flip top roof.

The other aspect is that it kept the stray light off from the sides – I’ve attached some images for reference.



Thanks,



Jack ~



From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@aol.com> via groups.io
Sent: Tuesday, August 18, 2020 1:47 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras



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@astro-physics.com>
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@aol.com> 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@intel.com>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Stone, Jack G <jack.g.stone@intel.com>
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@aol.com> 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@intel.com>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Jack Stone <mediwheel_js@sbcglobal.net>
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@aol.com> 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=yahoo.com@groups.io>
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@aol.com> via groups.io <chris1011=aol.com@groups.io> 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=yahoo.com@groups.io>
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@aol.com> 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:



<image001.png>


Re: Small Dome Amateur Observatories - Downsides

 

Don’t get me wrong; a roll off observatory is much better for imaging when possible. You can’t fully eliminate the heat issue on a dome no matter how hard you try because domes funnel heat past the aperture. My point is that there are some ways to partially mitigate the issue. Slatted domes are another method I have seen, but you would still be better off just removing the roof entirely.

 

Liam

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Stone, Jack G
Sent: Tuesday, August 18, 2020 16:04
To: main@ap-gto.groups.io
Cc: Stone, Jack G <jack.g.stone@...>
Subject: [ap-gto] Small Dome Amateur Observatories - Downsides

 

Renamed Subject:

 

Liam – Rolando has a point.

I have noticed that after time – the heat convection from my body does warm up the dome.

Most time I left the door open, but still heat rises.

 

Rolando – The dome just looked kool according to my wife.  Footprint for a roll-off will require presidential approval.

So other option is a flip top roof. 

The other aspect is that it kept the stray light off from the sides – I’ve attached some images for reference.

 

Thanks,

 

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 1:47 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

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:

 


Re: Exposure comparisons with CCD cameras

W Hilmo
 

I think that to understand what’s going on, you need to separate read noise from shot noise.

 

In the single 60 minute image, there is 60 minutes worth of signal, 60 minutes worth of shot noise and 1 instance of read noise.  In the 6 x 10 image, there is 60 minutes worth of signal, 60 minutes worth of shot noise and 6 instances of read noise.  In theory, I believe that the math suggests that with a zero read noise camera, there would be no difference in S/N between the two final images.  If I remember correctly, you are using a camera with a KAF-8300 CCD, which has pretty high read noise.  Also, you are imaging a narrow band object, so the signal level in the faint areas is very low.

 

If you were shooting RGB, or if you were using a camera with very low read noise, I’m guessing that the final comparison between the two results would be much closer.

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of uncarollo2 <chris1011@...> via groups.io
Sent: Tuesday, August 18, 2020 1:56 PM
To: main@ap-gto.groups.io
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.


Small Dome Amateur Observatories - Downsides

Stone, Jack G
 

Renamed Subject:

 

Liam – Rolando has a point.

I have noticed that after time – the heat convection from my body does warm up the dome.

Most time I left the door open, but still heat rises.

 

Rolando – The dome just looked kool according to my wife.  Footprint for a roll-off will require presidential approval.

So other option is a flip top roof. 

The other aspect is that it kept the stray light off from the sides – I’ve attached some images for reference.

 

Thanks,

 

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 1:47 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

 

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:

 


Re: Exposure comparisons with CCD cameras

CurtisC
 

Rolando, one of your comments in your post at the head of this thread caught my eye.  I use MaxIm and a Superstar for guiding (with the Baader guide scope).  My main scope is a TEC140ED.  Mount is a 2010 vintage Mach1.  I use 5 sec guiding exposures.  I believe MaxIm applies the corrections immediately after each guider exposure.  Can this be changed?  Is there a way in MaxIm to separate the guide exposure from the guide move?  I don't even know if I want to try it, but I'm interested in anything that improves control of my equipment.


Re: Exposure comparisons with CCD cameras

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.


Re: Exposure comparisons with CCD cameras

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.


Re: Exposure comparisons with CCD cameras

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:
--------------------------------------------------------------------
Daniel Borcard
Observatoire du Geai Bleu
Les faits sont têtus. Les nier ne les fait pas disparaître.
--------------------------------------------------------------------





Re: A couple of doubts about modeling and about not using guiding. #APCC #Mach2GTO

Roland Christen
 


1) How often do I need to redo the modeling,
Unless you change something on the setup, the model should work any time in any weather. Depends somewhat also on the pixel scale. If you are working at long focal lengths you would need to add an atmospheric pressure detector to add to the model terms.

Rolando


-----Original Message-----
From: Marcelo Figueroa via groups.io <marfig1970@...>
To: main@ap-gto.groups.io
Sent: Tue, Aug 18, 2020 3:20 pm
Subject: [ap-gto] A couple of doubts about modeling and about not using guiding. #Mach2GTO #APCC

Hi,
 
While waiting for the weather to finally allow me to test my Mach2 (it's winter here in the southern hemisphere), I have a couple of doubts about modeling:
 
(my installation is semi-permanent in my backyard)
 
1) How often do I need to redo the modeling, for example, do I need one for the winter and one for the summer?
 
2) If I change the camera, do I also need to redo the modeling?
 
 
One more thing. A small advantage of guiding is that it acts in fact as a weather monitor, if it gets cloudy the guide star is lost and the session is aborted. In the case of going unguided, how do I monitor the weather. Do I need any additional equipment?
 
Thank you,


Re: Exposure comparisons with CCD cameras

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.


Re: Exposure comparisons with CCD cameras

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@...


Re: Exposure comparisons with CCD cameras

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:
 


Re: Exposure comparisons with CCD cameras

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@...


Re: Exposure comparisons with CCD cameras

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@...


Re: Exposure comparisons with CCD cameras

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.
--------------------------------------------------------------------





A couple of doubts about modeling and about not using guiding. #APCC #Mach2GTO

Marcelo Figueroa
 

Hi,
 
While waiting for the weather to finally allow me to test my Mach2 (it's winter here in the southern hemisphere), I have a couple of doubts about modeling:
 
(my installation is semi-permanent in my backyard)
 
1) How often do I need to redo the modeling, for example, do I need one for the winter and one for the summer?
 
2) If I change the camera, do I also need to redo the modeling?
 
 
One more thing. A small advantage of guiding is that it acts in fact as a weather monitor, if it gets cloudy the guide star is lost and the session is aborted. In the case of going unguided, how do I monitor the weather. Do I need any additional equipment?
 
Thank you,


Re: 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:

 

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