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Background artifacts in 16200 Image

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#1 pbunn

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Posted 24 June 2019 - 10:28 PM

I am getting a strange background with my FLI 16200 camera as seen in this Hydrogen Alpha image. Is this the same thing others have mentioned? I see it in LRGB also but less pronounced.

 

Any help would be appreciated.

 

Thanks in advance.

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  • bubbleandopen.jpg

Edited by pbunn, 24 June 2019 - 10:38 PM.

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#2 BenKolt

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Posted 25 June 2019 - 09:04 AM

Pat:

 

Please provide a detailed description of your calibration steps.  Thanks!

 

Ben



#3 pbunn

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Posted 25 June 2019 - 11:43 AM

Ben

 

 For the above image, I used the script in PI and have not fine tuned the Image integration.

 

I ran subframe selector and blinked the images and then loaded them into the script. My bias and dark masters are  a few weeks old. My flats is a little older than that. I don't think it is a flats problem though.

 

Thanks for your help.

 

Pat


Edited by pbunn, 25 June 2019 - 11:43 AM.


#4 BenKolt

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Posted 25 June 2019 - 12:04 PM

Pat:

 

I suggest that you start working on this issue by running through a simple, manual calibration process. You'll want to first diagnose if your automatic process is inadvertently introducing or not removing the artifacts.

 

Make a master dark of same duration and temperature as your light frames.

 

When you take flats, where do you typically place the histogram in the range? This ought not to be too critical, but I have been advised with this camera to place it in the middle, even as high as at 2/3rds the full range.  I tend to target the 1/2 position.  I also like to take flat darks of same duration and temperature as the flat frames, but this also should not be too critical if you prefer to use bias frames.

 

I suggest you use these master frames for calibration, then register, then combine.

 

We'll see if that helps or if more diagnostics are to be done following this!

 

Good luck!

 

Best Regards,

Ben



#5 pbunn

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Posted 25 June 2019 - 01:33 PM

Thanks Ben. I tend to go at about 40 percent so I need to increase exposure on my flats . My Flip flat at DSW is stuck closed but help should arrive today and I can shoot a new set of Flats and I'll also shoot new bias and darks. I'll let you know what happens. 

 

Thanks again

 

Pat



#6 BenKolt

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Posted 25 June 2019 - 10:58 PM

OK, Pat.  Good luck with the Flip Flat problem!

 

Having the flat histogram at 40% was probably sufficient, and I doubt that alone is the cause of the artifacts in your combined image.  Something else is probably going on here.

 

I'm interested in seeing how a straightforward, simple calibration works on your frames followed by registration and combination.  I recommend that you be sure to not be using any kind of optimization or calibration with the dark or flat master creation steps.  Match exposures and temperatures between the light and dark frames.  Match the same between the flat and dark flat frames.  Hopefully the calibration will then work and there will be no underlying artifacts left in your final combined image.

 

If that is not the case, then there are a couple more things I would recommend that you check, however they become increasingly involved.

 

Best Regards,

Ben



#7 pbunn

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Posted 26 June 2019 - 03:54 PM

I did this using a pretty simple run through using David Ault's procedure but leaving out the extra stuff. Still has some strange background stuff.

 

The flats are not great and I have a new Flip Flat arriving at DSW on Friday. I'll try again with fresh ones then.

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#8 pbunn

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Posted 30 June 2019 - 09:26 AM

Any comments on the second image? Thanks



#9 BenKolt

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Posted 30 June 2019 - 12:44 PM

Any comments on the second image? Thanks

Sorry, I've been traveling.

 

I looked through David Ault's method just now and noticed that he covers a wide range of alternate steps, but that wasn't sufficient for me to determine exactly how you are calibrating.

 

This reason I'm pressing you to run through the simplest calibration procedure is to try to narrow down where the artifacts are (1) being introduced and/or (2) failing to be calibrated out. I learned through my own trial and error that calibration served me best when I kept it absolutely direct and simple.  For example, if somehow you are double bias subtracting or something like that, you could be messing yourself up.  I suggest that you post your procedure directly and in detail please.

 

The other thing that will be helpful is to see if this artifact pattern matches the underlying unevenness of the CCD itself.  Please post a stretched image of a single long exposure (say 15 min) uncalibrated dark taken at your usual cooling temperature.  You ought to see some banding and maybe some arcs that are left over from the processing steps when the sensor was made.  These patterns should be removed from light frames through dark subtraction when done properly.  I'm curious if these match what you are seeing.

 

Best Regards,

Ben




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