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NB darker than darks

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#1 jonkjon

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Posted 22 November 2020 - 11:42 AM

Recently, I was experiencing some issues calibrating my HA data (180s/gain 75) as they were all coming out mostly black. After some thought, (and experimentation), I realized the mean value of my darks was higher than the mean value of my HA data. I certainly couldn't use dark optimization effectively with my CMOS (QHY163M) so that was not an option. I solved this issue by manually calibrating the data using a pedestal value of 800DN on my HA calibration.

 

I then began wondering though, since there was clearly amp glow present in my data and my darks, would that cause my darks to be lighter than my HA. I did a quick test and shot a 3 min. dark using my LUM filter as I usually do and got a mean value of 595 which was higher than the mean of 576 for my HA. I then shot a 3 min. dark through my HA filter and indeed saw a drop to a mean value of 556. I always assumed that the filter shouldn't make any difference to my dark frames. Now, it looks like the amp glow is contributing enough light(?) to make a difference. I am certainly no expert here but is there any validity to this option or should I just keep using the pedestal value? It seems one benefit might be if someone had this issue and wanted to use WBPP and not worry about using the pedestal. It also occurred to me that I could/should have used a higher gain for the NB data.

 

Either way, this was a great learning experience!

 

 

--Jon


Edited by jonkjon, 22 November 2020 - 11:43 AM.


#2 dayglow

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Posted 22 November 2020 - 12:08 PM

How is the camera being capped when making darks ?



#3 jonkjon

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Posted 22 November 2020 - 12:14 PM

How is the camera being capped when making darks ?

With these darks, the dust cap, blackout curtain covering whole rig and covered with Orion telescope cover. All done indoors, at night in a dark room as well. I experimented a lot with this when i first discovered amp-glow because I thought it was a light leak.

 

--Jon



#4 rwstanley

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Posted 22 November 2020 - 03:14 PM

Hi Jon,

 

Are you using the latest drivers for your 163M?  There were issues in the past that caused the pedestal to change randomly and wreak havoc with darks and bias frames.  This is corrected in the latest drivers.

 

-Ron



#5 jonkjon

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Posted 22 November 2020 - 05:20 PM

Hi Jon,

 

Are you using the latest drivers for your 163M?  There were issues in the past that caused the pedestal to change randomly and wreak havoc with darks and bias frames.  This is corrected in the latest drivers.

 

-Ron

Ron,

 

Thanks for the suggestion. While I don't think I have the absolute latest, I am sure I have drivers more recent than when the pedestal issue appeared. These values are not random. This is consistent over hundreds of frames for at least 6 months. I don't always add HA to my lrgb runs but I did the last few sessions so that's when I ran into the problem. Thanks again...

 

--Jon

 

P.S. - Just because you mentioned it, I connected my gear and updated anyway! grin.gif  I'll let you know if there's any difference in my testing.


Edited by jonkjon, 22 November 2020 - 06:18 PM.


#6 jonkjon

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Posted 22 November 2020 - 06:43 PM

Discovered that I shot my last darks at the wrong offset! Shooting new darks now! Wow do I feel like a dummy! :bangbang:

I don't think SGP displays the offset prominently in the version I am using so I just didn't notice it. I decided to start using N.I.N.A. recently and it just popped out at me while testing. I believe I manually typed the directory name for my dark library and I inadvertently set it to the wrong offset and that's what I wound up using in the actual capture....live and learn.

 

Sorry for wasting everyone's time....but thanks for all the helpful suggestions.

 

--Jon




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