Date   

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

Marcelo Figueroa
 

Thank you, Ray. 
 
Will the smaller Mbox version work (cheaper) or does it necessarily have to be the V2?

https://www.astromi.ch/product/mbox/
 
Thanks again,


Re: APCC and MBoxV2 #APCC

Phillip Klein
 

Hi Bryan,

Thank you for letting me know APCC does work with MBoxV2. I just downloaded what may be a newer version. My equipment is at another location so I will try connecting in the GPS tab. I'm not sure that is how I tried connecting in the past.
If I still have a problem connecting I may circle back with you again.
Thank you very much for your reply.

Phillip

On Wed, Aug 19, 2020 at 11:04 AM Worsel via groups.io <bryancashion=yahoo.com@groups.io> wrote:
Phillip

Yes, I have had the MboxV2 for about 8 months.  The biggest challenge is remembering to Connect in the GPS tab.  I downloaded and installed the Astromi.ch Windows app which found the box, including the COM Port, which APPC needs.

Bryan


Re: Exposure comparisons with CCD cameras

Benoit Schillings
 

The best guess then is that your camera has significant readout noise
or quantization noise.

-- benoit

On Wed, Aug 19, 2020 at 9:43 AM uncarollo2 <chris1011@aol.com> via
groups.io <chris1011=aol.com@groups.io> wrote:


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.

Actually I did that. I tried combining 3 different ways median, average and sum. None of them came close to the sig/noise of the single exposure.

Roland


-----Original Message-----
From: Ray Gralak <groups3@gralak.com>
To: main@ap-gto.groups.io
Sent: Wed, Aug 19, 2020 9:17 am
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 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

Dean Jacobsen
 

It is rare that I would have that much of a temperature change after running a model.  That would probably only happen in the winter.
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Re: APCC and MBoxV2 #APCC

Worsel
 

Phillip

Yes, I have had the MboxV2 for about 8 months.  The biggest challenge is remembering to Connect in the GPS tab.  I downloaded and installed the Astromi.ch Windows app which found the box, including the COM Port, which APPC needs.

Bryan


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

Worsel
 

The APPC-Pro manual says changes to the model can become important if the temperature change is above 15 degrees C. (See screenshot of page 188). 

Bryan


APCC and MBoxV2 #APCC

Phillip Klein
 

Hello,

My question is anyone using APCC and MBoxV2 successfully, meaning the data from MBoxV2 is connected to APCC and the data from MBoxV2 is being received in APCC?

Thank you,

Phillip


APCC-Pro manual temperature/pressure entry question

Bob Benamati
 

Ray,

For some reason, the temperature entry box for the pointing model has disappeared. I thought maybe updating to the latest version would fix it, but unfortunately it hasn't. The pressure box IS still there, so not sure if this is truly abnormal (screenshot attached).

Not having a weather station, I originally created a model at 10C, and that info is what is still populating APPM whenever I've redone a model. Not sure where APPM is drawing that from and if I can/should change it when I do go to redo a model in the future.

Overall, APCC has been working wonders even for my old 900 CP3, so this is just more of a curiosity than an urgent need for resolution!

Thanks!
Bob


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

Dean Jacobsen
 

Also, I was just wondering if in the interim I can manually update the temperature and then have the tracking rate model adjusted 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

Bill Long
 

Plus you can manually input pressure. I just get reading at the start of the night and add 1 to it then plug that into APCC. I get the rest of the data from the Pegasus driver.


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Brian Valente <bvalente@...>
Sent: Wednesday, August 19, 2020 10:16 AM
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
 
Dean

I wouldn't get too caught up about pressure, it doesn't seem to impact the model that much and it doesn't really change that much either

this is a 2+ year graph of pressure at Obstech which essentially fluctuates between 85000 and 85500

I'm not suggesting this is representative of all weather patterns, only that it appears to have minimal impact on the modeling (Ray can confirm here)

image.png

On Wed, Aug 19, 2020 at 10:10 AM Dean Jacobsen <deanjacobsen@...> wrote:
On Wed, Aug 19, 2020 at 07:20 AM, Ray Gralak wrote:
Bill is correct! You should use some environmental measurement device, such as MGBox V2.
I am assuming then that the temperature and pressure information is applied to the tracking rate calculations and the tracking rate is adjusted in real time.  Is this correct Ray?
 
--
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

I wouldn't get too caught up about pressure, it doesn't seem to impact the model that much and it doesn't really change that much either

this is a 2+ year graph of pressure at Obstech which essentially fluctuates between 85000 and 85500

I'm not suggesting this is representative of all weather patterns, only that it appears to have minimal impact on the modeling (Ray can confirm here)

image.png

On Wed, Aug 19, 2020 at 10:10 AM Dean Jacobsen <deanjacobsen@...> wrote:
On Wed, Aug 19, 2020 at 07:20 AM, Ray Gralak wrote:
Bill is correct! You should use some environmental measurement device, such as MGBox V2.
I am assuming then that the temperature and pressure information is applied to the tracking rate calculations and the tracking rate is adjusted in real time.  Is this correct Ray?
 
--
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 Wed, Aug 19, 2020 at 07:20 AM, Ray Gralak wrote:
Bill is correct! You should use some environmental measurement device, such as MGBox V2.
I am assuming then that the temperature and pressure information is applied to the tracking rate calculations and the tracking rate is adjusted in real time.  Is this correct Ray?
 
--
Dean Jacobsen
http://astrophoto.net/wp/
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Re: Exposure comparisons with CCD cameras

Roland Christen
 


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.
Actually I did that. I tried combining 3 different ways median, average and sum. None of them came close to the sig/noise of the single exposure.

Roland


-----Original Message-----
From: Ray Gralak <groups3@...>
To: main@ap-gto.groups.io
Sent: Wed, Aug 19, 2020 9:17 am
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 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@...> 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@...> 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@...>
> > 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@...> 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

Bill Long
 

It's worth the full price imo. 


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Michael 'Mikey' Mangieri <mjmangieri@...>
Sent: Wednesday, August 19, 2020 6:33 AM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Cc: Tom Blahovici <tom.va2fsq@...>
Subject: Re: [ap-gto] A couple of doubts about modeling and about not using guiding. #Mach2GTO #APCC
 
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: Exposure comparisons with CCD cameras

Daniel Borcard
 

Here is a point that may be important:

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

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

Statistically speaking, as an estimator of central tendency, median has a larger standard error than arithmetic mean: the median value varies more from one estimation to the other than the mean value. Here, every pixel shows an independent estimation of the sky background level. Consequently, a median combination does show a noisier background, especially with a small number of subs, because the value of the sky background as estimated by the median varies more from one pixel to the other than the mean does.
I second Benoit's suggestion: try a mean combination. 
In true life I always use mean, with rejection measures for hot pixels or extreme values (e.g. satellites): hot pixel mapping, sigma (i.e., standard deviation) rejection where pixels are rejected from the mean calculation if their value are too extremely outlying.

Daniel

--------------------------------------------------------------------
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

Ray Gralak
 

Are focuser temperature probes supported like to Moonlite NightCrawlers?
If it has an ObservingConditions ASCOM driver, it is supported by APCC/APPM.

-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 Tom Blahovici
Sent: Tuesday, August 18, 2020 10:05 PM
To: 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

Ray Gralak
 

Bill Long wrote:
Per my chat with Ray, having accurate temperature data is THE most important thing.
Bill is correct! You should use some environmental measurement device, such as MGBox V2.

-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 Bill Long
Sent: Tuesday, August 18, 2020 7:16 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] A couple of doubts about modeling and about not using guiding. #Mach2GTO #APCC

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@gmail.com>
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
<https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fgroups.io%2F&data=02%7C01%7C%7
Cff49cc44eb86452e452508d843e1d69c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637333984
524927503&sdata=6hFEPebM8u0bu12F5kb1wJHxYyap1QXRc0yrzumZKpE%3D&reserved=0>
<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
portfolio brianvalentephotography.com
<https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fbrianvalentephotography.com%2F&dat
a=02%7C01%7C%7Cff49cc44eb86452e452508d843e1d69c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%
7C0%7C637333984524937496&sdata=CgG1Hxi6TZQ%2Fmf%2BghCFGJ7qhQ7Q%2FxHxqTWsX3I1A4d4%3
D&reserved=0>


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
 

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