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noisy integration results


(@cheastside)
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Joined: 2 years ago
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new camera(asi071 mc pro) and getting what seems to be pretty noisy stack from 7 hours of data on M45.  i'm wondering if something is wrong with my calibration files?  could you look them over?

Wo gt81 w/0.8 flattener
Asi071mc pro, unity gain/offset, 90/65
Asi224 guide cam
Wo unicam 32
Heq5 pro
Lights 295 @ 90s
60 of each Darks, dark flats, and flats
Bortle 4
No filters
 
the integrated stack and the master calibration files are here:
 
thanks!

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(@vincent-mod)
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I'll have a look, but given the fact that each sub is just 90s, that would explain more noise. Problem then is that your signal per subs is closer to the noise-floor of the sensor and adding more data improves that, but not dramatically so. You need to try to get signal above at least the noise floor. I'll check if that's the case.


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(@vincent-mod)
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Had a look at the integration, could you upload a few subs as well? Other than that the noise looks normal to me, the challenge with this object is to get the nebulosity nice as well as the bright stars. APP doesn't have HDR yet, so that is a bit more challenging and people tend to combine different exposure lengths in other programs. For this object you'd want to expose longer to get the nebulosity and short for the bright stars. Future versions of APP will have noise reduction as well which could also help here a bit.

 


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(@cheastside)
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Posted by: @vincent-mod

Had a look at the integration, could you upload a few subs as well? Other than that the noise looks normal to me, the challenge with this object is to get the nebulosity nice as well as the bright stars. APP doesn't have HDR yet, so that is a bit more challenging and people tend to combine different exposure lengths in other programs. For this object you'd want to expose longer to get the nebulosity and short for the bright stars. Future versions of APP will have noise reduction as well which could also help here a bit.

 

cool thanks Vincent!  i just uploaded several of the lights files.  that would be cool to have an hdr feature in app.  i know i needed longer exposures for that fainter nebulosity but held back for the stars, which did get blown out a bit anyways.  i guess i was hoping the additional integration time would make up for the shorter exposures.


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(@vincent-mod)
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It does indeed, but when the signal is really amongst the noise, it gets tricky. You can actually see this in your single subs, move with the mouse over the stars, up in the APP window you can see the pixel values, these indicate the stars are indeed already clipping. If you go to background you can see the values as well and they are basically the same for the areas with nebulosity. Your result is actually very good considering this.


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(@vincent-mod)
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Are you also dithering between images? That definitely helps as well with fixed pattern noise and such (not with read-out noise though).


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(@cheastside)
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@vincent-mod

yes dithering every third frame.  Using nina


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(@wvreeven)
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@cheastside To add to Vincent's questions, how much do you dither? Note that dithering of at least 15, but better 20, pixels in the imaging camera is necessary. AFAIK all imaging software let you specify the amount of pixels for the guide camera so you'll need to compute the guide camera dither offset using the desired imaging camera offset and the plate scales of the two cameras.


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(@cheastside)
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Posted by: @wvreeven

@cheastside To add to Vincent's questions, how much do you dither? Note that dithering of at least 15, but better 20, pixels in the imaging camera is necessary. AFAIK all imaging software let you specify the amount of pixels for the guide camera so you'll need to compute the guide camera dither offset using the desired imaging camera offset and the plate scales of the two cameras.

excellent and thanks for the clarification Wouter!  sorry, newb here.  it looks like nina is dithering 5 px.  see attached pic.  so i should change that to 20?  i have to read up on this.  man the layers to this onion are unreal!!

Screen Shot 2021 12 01 at 5.33.17 AM

 


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(@wvreeven)
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Posted by: @cheastside

excellent and thanks for the clarification Wouter!  sorry, newb here.  it looks like nina is dithering 5 px.  see attached pic.  so i should change that to 20?  i have to read up on this.  man the layers to this onion are unreal!!

Once again, NINA is dithering 5 px in the GUIDE camera and you should strive for 20 pix in the IMAGING camera. This website

https://astronomy.tools/calculators/ccd

allows you to compute the plate scale of the guide and imgaing cameras given the guide and imaging telescope specs, respectively. If your guide camera has a plate scale of p_guide and the imaging camera of p_imaging, then you need to make sure that NINA is set to dither 20 x p_guide / p_imaging pixels.


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(@cheastside)
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Posted by: @wvreeven
Posted by: @cheastside

excellent and thanks for the clarification Wouter!  sorry, newb here.  it looks like nina is dithering 5 px.  see attached pic.  so i should change that to 20?  i have to read up on this.  man the layers to this onion are unreal!!

Once again, NINA is dithering 5 px in the GUIDE camera and you should strive for 20 pix in the IMAGING camera. This website

https://astronomy.tools/calculators/ccd

allows you to compute the plate scale of the guide and imgaing cameras given the guide and imaging telescope specs, respectively. If your guide camera has a plate scale of p_guide and the imaging camera of p_imaging, then you need to make sure that NINA is set to dither 20 x p_guide / p_imaging pixels.

ok, bear with me on this.  i was using astronomy tools as you wrote your reply.  i get the following for my setup,

guide camera imaging scale=6.45 arcsec/px

imaging scale of main camera and scope=2.78 arcsec/px

per nina's instruction manual:

It is usually recommended to dither a number of guide camera pixels that will shift the main imaging camera of about 10 pixels.

so aiming for a 10px shift in the main camera, then i should set NINAs PHD2 dither Pixel setting to 4.

BUT, you're saying 15-20 pixel at the imaging camera instead of 10 correct?  if so then i need to change that setting to 7 to 9.

should this be 20xp_imaging px/p_guide?

Screen Shot 2021 12 01 at 6.33.48 AM

 


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(@wvreeven)
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@cheastside The plate scale of your guide cam is much larger than that of the imaging camera. This means that 1 pixel in the guide camera corresponds to 1 x p_guide / p_image = 2.32 pixels in the imaging camera. So a dither in the image camera of 15 to 20 pixels corresponds to a dither of 15 / 2.32 = 6.5 to 20 / 2.32 = 8.6 pixels in the guide cam.

In other words, if you aim for a dither of D pixels in the imaging cam then you'll need to set NINA to D / 2.32 = D / (p_guide / p_image) = D * p_image / p_guide pixels.

In reverse, if you set the dithering to d pixels in NINA then this will correspond to d * 2.32 = d * p_guide / p_image pixels in the imaging camera.

Sorry, I got the formula the wrong way around.


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(@cheastside)
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@wvreeven

Thanks for excellent feedback!   Ive changed the setting in nina from 5 to 9.  The setting of 5 was equating to a 12px movement at the imaging cam.  9 should equate to about 20    Im curious to see the difference

 

im assuming from what vincent said earlier that my calibration files are working as expected?

 


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(@vincent-mod)
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I think they are yes. The dithering steps removes fixed pattern noise, so your result will still be "noisy" regarding random noise. But it helps a ton with all kinds of bigger and fixed pattern noise.


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(@cheastside)
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@vincent-mod

@wvreeven

thanks guys for your excellent help with this.  not only to confirm APP was working and my calibration files but also adding very helpful insight on the image noise.  i'm also currently imaging horsehead and flame nebulas with the same camera and setup, but it is coming out very clean and noiseless as i was expecting to see in this image.  clearly i didn't expose this one well enough for the fainter nebulosity.  Plus i also learned about dithering settings!  so much to learn!


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