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SGP image statistics help

astrophotography
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#1 Mte1022

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Posted 06 April 2020 - 10:29 PM

Hi everyone,

I recently switched to mono ap. I’ve gotten as far as learning how to organize, stack and process (basic). However, I notice that my images seem noisy pre processing, before I combine the channels. I’m shooting narrowband (astronomik 6nm).

I’ve been experimenting with a sw esprit 100 and an edge 800. More so on the refractor. The camera is an asi1600mm-pro. Temp is set to -20. Gain 200, offset 50. I’m in a bottle 6-7 zone (Palm Springs area).

I’ve done a lot of research, but I’m at the point where I just need to ask. I don’t quite understand the 12bit vs 16 bit. I also don’t understand how to decipher the image statistics. Where should I be? What stat should I be focusing on? Any help/guidance would be much appreciated.

a08166140661cd70b8ba8b24528c2854.jpg


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#2 Peregrinatum

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Posted 06 April 2020 - 11:34 PM

The image statistics give you real time feedback on what your camera is capturing... this is what I look at:

 

Image>mean =  this is the average adu value of your overall image, this tells you if your exposure is optimal, you need to determine beforehand at what level you want to dilute your the camera read noise, and this metric tells you if you are hitting it

 

Image>maximum = tells you if you are over exposing, you move the cursor around the image to see if the over exposure is from blown out stars or your object (look in the "sampling" section to see the max adu), if just stars then no worries but if from your target then you need to dial back the exposure

 

Stars found = tells me how dark my skies are, optimally this will increase as the night goes on toward to meridian, then slowly decrease... it tells me if I have thin passing clouds and may have focus problems

 

Half Flux Radius = tells me how my focus is holding... as the night goes on and it gets colder this metric will slowly drift higher telling me when it is time to refocus, autofocus is nice here


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#3 oshimitsu

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Posted 06 April 2020 - 11:50 PM

12 v 16 bit is the bit depth of your image. You need to look at the manufactures information for the ASI183. A quick google search looks like it captures in 12 bit but you can capture in 10bit to get more FPS


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#4 Peregrinatum

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Posted 06 April 2020 - 11:54 PM

just a note: regardless of what bit depth your camera is sgp will always give you 16 bit readings in the statistics


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#5 Stelios

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Posted 07 April 2020 - 01:01 AM

Your camera provides 12-bit results, but SGP translates to 16 bit (basically, multiplies by 16 :)). 

 

You might as well forget the bit depth, and just look at the 16-bit results. The maximum value is 65535 (that would be pure saturated white). 0 would be perfect black. Mean, Median, Standard Deviation are the standard statistical terms, minimum and maximum should be obvious (minimum is not 0 because space is not black, given the atmosphere). 

 

You can toggle HFR (Half-Flux-Radius) by clicking on the star in the symbol bar at the top of the image. HFR is a great measure of focus. You are perfectly focused at the minimum--an autofocuser finds that value and zeroes in. 

 

Your gain and offset values are high. You should use 200 with narrowband only. In the beginning, I would just go with the default 139 gain and default offset, until you have some experience.

 

There are calculators on the site as to how to find ideal exposures based on swamping the read noise. Perhaps someone will look up the thread (I don't have time right now).


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#6 RudiVM

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Posted 07 April 2020 - 03:31 AM

This might be the thread Stelios is refering to: 

 

https://www.cloudyni...d-maybe-qhy163/

 

HTH.




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