Date   

Re: Exposure comparisons with CCD cameras

Ray Gralak
 

Median combined can be an issue for very slight background variation.
How confident are you of the software auto-scaling... I would do a
simple mean for the comparaison, even if you end up with a few hot
pixels
Benoit is right.

Roland, you should try averaging the six ten minute exposures. The S/N will be higher, and the result should look closer to the single 60-minute image.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Benoit Schillings
Sent: Tuesday, August 18, 2020 7:10 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

Median combined can be an issue for very slight background variation.
How confident are you of the software auto-scaling... I would do a
simple mean for the comparaison, even if you end up with a few hot
pixels

-- benoit

On Tue, Aug 18, 2020 at 6:07 PM W Hilmo <y.groups@hilmo.net> wrote:

“I'm not shooting RGB, I'm shooting NB where the 10 min object signal is at 700 or so out of 65,000.”



I realize that you weren’t shooting RGB, and I know that you can’t do a single 60 minute broad band exposure
without saturating the sensor. I am saying that if you were shooting RGB (and if the sensor had sufficient well
depth to deal with that), I would expect the two results to be closer to each other. The reason for that is that
that the dominant noise would be shot noise from a much higher signal in the background sky. Since you are
shooting narrow band, both the signal and shot noise are very small. That makes the read noise relatively
more significant.



In terms of S/N, the difference between 1x3600 seconds and 6x600 seconds is the read noise of the camera.
You may also be giving up something by using median combine instead of a combination of statistical rejection
and mean combine – but the specifics of that are less clear to me.



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 2:53 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras





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.

I'm not shooting RGB, I'm shooting NB where the 10 min object signal is at 700 or so out of 65,000. And the
faintest detail in the thin wisps next to the brightest part are on the order of 160 in that exposure time. In the 1
hour exposure they are 6 times higher, which is still low compared to the max level before saturation. I could go
10 hours before reaching saturation of the brightest part of the nebula.



I was not trying to compare RGB, only Narrowband for extremely faint objects. I cannot do RGB here due to
massive light pollution, so it's a moot point. I'm simply saying that for very faint stuff, long exposure NB has an
advantage. It's not only me, but others have shown similar results. The noise in the CCD is the same for both
exposures - that is, the noise produced by the camera is high for both images. The download noise may be the
limiting factor, so therefore it behooves to increase the exposure time and thus minimize the number of
downloads if you want to capture the faintest possible detail.



By the way, I have changed the image posted on AstroBin with some more info.

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



Rolando





-----Original Message-----
From: W Hilmo <y.groups@hilmo.net>
To: main@ap-gto.groups.io
Sent: Tue, Aug 18, 2020 4:06 pm
Subject: Re: [ap-gto] Exposure comparisons with CCD cameras

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@aol.com> 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=aol.com@groups.io>
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: A couple of doubts about modeling and about not using guiding. #APCC #Mach2GTO

Ray Gralak
 

Hi Marcelo,

1) How often do I need to redo the modeling, for example, do I need one for the winter and one for the
summer?
It depends on your equipment. If you don't change anything over the entire year, the model will provide much better pointing and tracking accuracy then without a model.

However, significant changes in temperature can change the amount of flexure in the equipment. Thus a new model might provide higher pointing and tracking accuracy. One of the things I have been experimenting with is modeling the changes in the model not accounted for by just atmospheric refraction changes. This functionality may make it into a future release of APCC. It works by analyzing differences in pointing errors over time and temperature. It can do this because APPM saves the temperature, pressure, and humidity with each sky data point. This particular technique uses machine learning to predict and dynamically adjust pointing/tracking rates based on temperature changes.

One other thing that might affect your model if you are not using a permanent pier is ground shifting/expansion/contraction. This can cause your polar alignment to move around a bit and thus affect pointing and tracking rate accuracy.

Luckily, it is very easy to build a new model with APPM. You should be able to do at least 2-3 data points per minute, so in only 30-45 minutes you can have a fresh new model.

2) If I change the camera, do I also need to redo the modeling?
Maybe. It depends on the rigidity of the telescope and the difference in weight between the two cameras. Even so, using a model for a different camera will be better than no model.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Marcelo Figueroa via groups.io
Sent: Tuesday, August 18, 2020 1:20 PM
To: main@ap-gto.groups.io
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: APPM and color cameras #APCC

Dean Jacobsen
 


Re: APPM and color cameras #APCC

Ray Gralak
 

Hi Dean,

I haven't tried a color camera, but to keep memory utilization down, whatever camera application used should be configured to prevent debayering the raw camera data into a FITS image with three color planes. Color is not used for plate-solving, so leaving the raw data as is will be fine.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Dean Jacobsen
Sent: Tuesday, August 18, 2020 6:52 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] APPM and color cameras #APCC

No responses so I guess it must have been a dumb question. :-)
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ <https://www.astrobin.com/users/deanjacobsen/>


Re: Exposure comparisons with CCD cameras

Len Fulham
 

Liam et al, Re Dome heat plumes.

I tried A/C in my domed obs and I was not very satisfied with the result. It seemed the cold air inside the dome still was interacting with the external air causing issues. It was also expensive over time. When the A/C died, I decided to try a different tack - I installed a 18" variable speed exhaust fan in one wall. I turned it on high coming into evening and slowed it down later (so it was not too noisy). Drawing air into the dome seemed to stop plumes from forming and I experienced better seeing. On the other hand, there was a exhaust plume on one side of the observatory which did affect seeing in that direction (A/C, if running at night, are worse!).

The fan was reversible, I tried it blowing into the obs, that was seriously worse.

At a different site I had a slide off roof, the seeing was almost always better there. I also enjoyed the open aesthetic of the slide off roof, always more fun (mostly visual).

I think a dome wins when you want light/wind shielding esp imaging or for remote operation.

Len.


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

Michael 'Mikey' Mangieri
 

Based upon what Bill Long and others have said it looks like modeling even with a non-permanent pier is really something to consider. Too bad I let the discount period lapse on getting APCCPro as I didn’t think it was something I would need until after I get my obsy.  

Mikey


On Aug 19, 2020, at 2:21 AM, Bill Long <bill@...> wrote:


It doesn't have an ASCOM Observing Conditions driver, so no.


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Tom Blahovici <tom.va2fsq@...>
Sent: Tuesday, August 18, 2020 10:04 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] A couple of doubts about modeling and about not using guiding. #Mach2GTO #APCC
 
Are focuser temperature probes supported like to Moonlite NightCrawlers?
Tom


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

Bill Long
 

It doesn't have an ASCOM Observing Conditions driver, so no.


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Tom Blahovici <tom.va2fsq@...>
Sent: Tuesday, August 18, 2020 10:04 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] A couple of doubts about modeling and about not using guiding. #Mach2GTO #APCC
 
Are focuser temperature probes supported like to Moonlite NightCrawlers?
Tom


Re: Correction to a CN post

Tom Blahovici
 

No, the model in the CP4.


Re: Correction to a CN post

Konstantin von Poschinger
 

What? If you mean the Model in the hand pad, No. 

Konstantin

Am 19.08.2020 um 06:49 schrieb Tom Blahovici <tom.va2fsq@...>:

Hi,
Is this now available?


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

Tom Blahovici
 

Are focuser temperature probes supported like to Moonlite NightCrawlers?
Tom


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

Dean Jacobsen
 

Yes we did.  :-)  And it is on the “to do” list, but haven’t been able to get out to the observatory yet.  I will pester you if I can’t figure it out.
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


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

 

Dean i realize we may have talked about this a few posts ago :)

I do think your skybox can generate a boltwood file, you just need to figure out how to store that to an accessible folder for your computer

Happy to share what we've done here offlist if you like

On Tue, Aug 18, 2020 at 9:50 PM Dean Jacobsen <deanjacobsen@...> wrote:
On Tue, Aug 18, 2020 at 09:42 PM, Brian Valente wrote:
FYI if you are at a shared remote obs they often have a boltwood file available from their environmental sensors that is available for use, and that also work for APPM
Yes, I put up a Sky Alert box when we installed the roof system.  It is on our network as an Ethernet device. I haven’t been able to test whether I can connect up with it through ASCOM yet because the weather hasn’t been cooperating this cycle.
 
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 



--
Brian 



Brian Valente


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

Dean Jacobsen
 

On Tue, Aug 18, 2020 at 09:42 PM, Brian Valente wrote:
FYI if you are at a shared remote obs they often have a boltwood file available from their environmental sensors that is available for use, and that also work for APPM
Yes, I put up a Sky Alert box when we installed the roof system.  It is on our network as an Ethernet device. I haven’t been able to test whether I can connect up with it through ASCOM yet because the weather hasn’t been cooperating this cycle.
 
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Re: Correction to a CN post

Tom Blahovici
 

Hi,
Is this now available?


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

 

FYI if you are at a shared remote obs they often have a boltwood file available from their environmental sensors that is available for use, and that also work for APPM 

this is what we use at Obstech (chile) as our MGBOx is not currently working correctly



On Tue, Aug 18, 2020 at 9:38 PM Dean Jacobsen <deanjacobsen@...> wrote:

[Edited Message Follows]

Thanks Bill and Brian.  This is something that I want to incorporate then.

We get pretty significant temperature changes throughout the night so keeping track of the difference between when the model was made and then during imaging might be something I would want to do.
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 



--
Brian 



Brian Valente


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

Joseph Beyer
 

Thanks for confirming.

On Tue, Aug 18, 2020 at 9:09 PM Brian Valente <bvalente@...> wrote:
That will work for model building, but you need the current temperature as you are imaging, so you really need a way where the temperature is updated on a consistent basis.

the modeling adjusts based on temp at time of modeling and current temp when imaging

On Tue, Aug 18, 2020 at 8:56 PM Joseph Beyer <jcbeyer2001@...> wrote:
I don't own an environmental sensor that interfaces directly with my computer but I manually enter current temperature and barometric pressure from my backyard weather station into the APCC-Pro Pointing Model tab when I run a model.  The data is pulled through to APPM and I assume used in the calculation of the pointing and tracking model.  Is this assumption correct?

On Tue, Aug 18, 2020 at 7:16 PM Bill Long <bill@...> wrote:
Per my chat with Ray, having accurate temperature data is THE most important thing. 


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Brian Valente <bvalente@...>
Sent: Tuesday, August 18, 2020 6:47 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] A couple of doubts about modeling and about not using guiding. #Mach2GTO #APCC
 
HI Marcelo

Temperature does have some impact on the modeling (talking with Ray on this) so you might consider having an environmental sensor in there like an MGBox V2

On Tue, Aug 18, 2020 at 6:17 PM Marcelo Figueroa via groups.io <marfig1970=yahoo.com@groups.io> wrote:
OK, thank you very much. Good to know. :)
 
My telescope is an Esprit 100, so I guess I don't need an atmospheric pressure detector at the moment.



--
Brian 



Brian Valente



--
Brian 



Brian Valente


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

Dean Jacobsen
 
Edited

Thanks Bill and Brian.  This is something that I want to incorporate then.

We get pretty significant temperature changes throughout the night so keeping track of the difference between when the model was made and then during imaging might be something I would want to do.
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


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

 

Dean

Ray is probably best to answer, but i've had long talks with him on this and yes, MGBox (or something similar) provides updated temperatures, and the APPM modeling takes the temperature into account when adjusting the tracking in real time

When Ray says temperature is important, i'm fairly certain the above is what he is referring to

On Tue, Aug 18, 2020 at 9:24 PM Dean Jacobsen <deanjacobsen@...> wrote:
If one were to employ a MGBox does the software adjust or update the model in real time as the temperature changes, and, if so, are these adjustments to the model updated into the tracking rate correction in real time?
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 



--
Brian 



Brian Valente


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

Bill Long
 

Yes there is an environment poll that APCC does. The sensor provided with the Pegasus Ultimate Powerbox v2 and Powerbox Advance (cheaper) works perfectly with APCC. 


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Dean Jacobsen <deanjacobsen@...>
Sent: Tuesday, August 18, 2020 9:24 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] A couple of doubts about modeling and about not using guiding. #Mach2GTO #APCC
 
If one were to employ a MGBox does the software adjust or update the model in real time as the temperature changes, and, if so, are these adjustments to the model updated into the tracking rate correction in real time?
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


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

Dean Jacobsen
 

If one were to employ a MGBox does the software adjust or update the model in real time as the temperature changes, and, if so, are these adjustments to the model updated into the tracking rate correction in real time?
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 

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