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What to do on a moonlit night?

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#26 GoFish

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Posted 17 September 2019 - 12:19 PM

Some progress last night, but the green gradient is still not solved frown.gif

 

I balanced the color using the White(R\) and White(B) sliders while looking at a representative slice of sky.  Check.  Nice neutral background in the live window, which is really nice!

 

Then I shot darks and flats, using the balanced color.

 

When stacked images are heavily stretched, though, the green gradient reappears in all its glory.  I tried a stack without using darks calibration, and the result is virtually identical.  So "bad" darks don't seem to be the issue.  (I thought it was very odd that there was no difference between results with and w/o applying darks, though.)

 

I examined my master flat frame, and it does not have any right-to-left gradient (a tiny bit of up-down, but no left-right).  So I don't think this is caused by flats.  I cannot test without applying flats, though, because the vignetting in the uncalibrated stretched image overwhelms the gradient.  So the flats are doing their job, it seems.

 

My next troubleshooting step probably needs to be capturing a series of raw FTS lights, darks, and flats and running them through DSS.  This will eliminate any possible issues with the way SharpCap is doing dark and flat calibration, or histogram stretching.

 

Pelican nebula, 9 frames @ 30s = 270s.  AT8IN, ASI294MC at -5C.  SharpCap Pro.  Saved with adjustments, downsampling and JPG conversion in PS.

pelican-1000-Stack_9frames_270s.jpg

 

 

 

 



#27 39.1N84.5W

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Posted 17 September 2019 - 01:12 PM

I'd try a different filter then. It is an improvement though!

#28 saguaro

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Posted 17 September 2019 - 01:38 PM

Some progress last night, but the green gradient is still not solved frown.gif

 

I balanced the color using the White(R\) and White(B) sliders while looking at a representative slice of sky.  Check.  Nice neutral background in the live window, which is really nice!

 

Then I shot darks and flats, using the balanced color.

 

When stacked images are heavily stretched, though, the green gradient reappears in all its glory.  I tried a stack without using darks calibration, and the result is virtually identical.  So "bad" darks don't seem to be the issue.  (I thought it was very odd that there was no difference between results with and w/o applying darks, though.)

 

I examined my master flat frame, and it does not have any right-to-left gradient (a tiny bit of up-down, but no left-right).  So I don't think this is caused by flats.  I cannot test without applying flats, though, because the vignetting in the uncalibrated stretched image overwhelms the gradient.  So the flats are doing their job, it seems.

 

My next troubleshooting step probably needs to be capturing a series of raw FTS lights, darks, and flats and running them through DSS.  This will eliminate any possible issues with the way SharpCap is doing dark and flat calibration, or histogram stretching.

 

Pelican nebula, 9 frames @ 30s = 270s.  AT8IN, ASI294MC at -5C.  SharpCap Pro.  Saved with adjustments, downsampling and JPG conversion in PS.

attachicon.gif pelican-1000-Stack_9frames_270s.jpg

Something to try: do your color balance once you’ve framed your target. You may have LP gradients that are different from the location you pointed at to do your color balance. If that doesn’t result in any improvement then try a different filter as Nick suggested.


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#29 Umasscrew39

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Posted 20 September 2019 - 09:01 AM

Something to try: do your color balance once you’ve framed your target. You may have LP gradients that are different from the location you pointed at to do your color balance. If that doesn’t result in any improvement then try a different filter as Nick suggested.

 

A couple of more suggests if you are still having problems:

 

1.  Instead of, "Saved with adjustments, downsampling and JPG conversion in PS", try saving as RAW 32 FITS files and then color balance and stretch in PS.  I use PI instead but PS should allow you to do the same thing.  This is the second option in SC under SAVE.  The option you chose (#3 under SAVE) should be good for minor tweaking and I tried that but the results are not very good in PI.  The second option really more typical post-processing and it brings out the best in your stack.  Now, if the results still do not make you happy, this leads to my second suggestion which is actually what Nick suggested.............

 

2.  Try a different filter.  I have been using the Optolong L-Enhance filter and the results are very impressive on emission nebulae, during a full moon or not.   That should improve your live views as well as in the post-processing of them. 

 

Best of luck     


Edited by Umasscrew39, 20 September 2019 - 09:42 AM.

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#30 GoFish

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Posted 20 September 2019 - 10:00 AM

A couple of more suggests if you are still having problems:

 

1.  Instead of, "Saved with adjustments, downsampling and JPG conversion in PS", try saving as RAW 32 FITS files and then color balance and stretch in PS.  I use PI instead but PS should allow you to do the same thing.  This is the second option in SC under SAVE.  The option you chose (#3 under SAVE) should be good for minor tweaking and I tried that but the results are not very good in PI.  The second option really more typical post-processing and it brings out the best in your stack.  Now, if the results still do not make you happy, this leads to my second suggestion which is actually what Nick suggested.............

 

2.  Try a different filter.  I have been using the Optolong L-Enhance filter and the results are very impressive on emission nebulae, during a full moon or not.   That should improve your live views as well as in the post-processing of them. 

 

Best of luck     

During my most recent session (using HyperStar C8) I did switch filters. This time IDAS LPS D1. 

 

The gradient was different, but still present to varying degrees. I’m having trouble identifying a pattern as to when, where, and how bad the gradients are!

 

My primary goal is to get to where real-time stacks look as good as possible. I think there are still a couple of improvements I can make to flats (longer exposures and calibrating the flats with dark flats instead of bias frames). 

 

One of these nights I’ll also capture some traditional raw files for later processing with DSS and PS. It will be interesting to see if the same gradients appear in DSS stacks as in SharpCap stacks. 




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