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Help Processing, well help with everything!

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#1 Bubbadawg

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Posted 20 January 2019 - 05:06 PM

I need advise on processing etc. I went out a week ago in front yard and got about 10 to 12 exposures @ 8 seconds each of M31, and a handful of darks, no bias, no flats and processed in DSS and Gimp.  Not great, but not ridiculously terrible. I went out last night and got about 40 exposures @ 15 seconds each, with 20 darks, flats and bias.  Again processed in DSS and Gimp.  Why does the 1st image seem better than the others that were done "properly" with lights, darks, bias and flats?  I don't understand.  Also, why is bottom 1/4 of image blown out and so crappy? I tried gradient tool but no luck really. The moon was high and bright both nights so not ideal conditions but I had nothing else to do so went out for a bit and my boys wanted to tag along so we had a good time goofing off and looking through scope.  Anyway, can someone please take a look and point me in right direction? Maybe even try to take my stacked unprocessed files and see if can even get a decent image stretched out of it (not sure how to do that unless I email to you or upload somewhere but need all help I can get). Needless to say, after watching a million youtube tutorials on this I am highly frustrated. Why is this so fun yet so frustrating? I guess I am a glutton for punishment or just chasing that holy grail of images. 

 

Test 1 image is about 10 x 8 seconds with about 10 darks ISO 3200 if I remember correctly

Test 2 is about 40 x 15 seconds with about 25 darks, bias and flats 1600 ISO

Test 3 is about 40 x 15 seconds with about 25 darks, bias, no flats as I was just trying to experiment. 1600 ISO

Attached Thumbnails

  • test1.jpg
  • test2.jpg
  • test3.jpg

Edited by Bubbadawg, 20 January 2019 - 05:11 PM.


#2 Eric Horton

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Posted 20 January 2019 - 05:45 PM

I just copied one of your images and did a little stretching.  The images you posted still need a lot of stretching in order to pull the data out.  The data is there but the moon was killing you.  In addition, there's just not enough exposure time.  I would suggest trying again with no moon and probably drop your iso down to 800 or 400.  Of course get as much time as you can.  I just did m31 last month with 36 subs at 300s each.  ISO 800.  



#3 Mark326

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Posted 20 January 2019 - 06:03 PM

I suspect there may be more data in your second batch of images that just needs to be teased out via additional stretching.  On my device, the background sky still appears quite dark. 

 

Im not really knowledgeable on DSLR photography but did notice the ISO setting 1600 vs 3200 change as well. I equate this to gain on Astro cameras.  What I believe you are gaining is more dynamic range with lower setting at the cost of exposure time needing to be longer.   There is a formula involved, (square root of something Time something) Charles Bracken book, Deep Sky Image Primer explains well regarding signal to noise.  Long story short, think by reducing your ISO you would have needed more exposure time to achieve similar brightness level in the base sub exposures.

 

if you make you subs, ect available for download. I’d be happy to give the data a shot in PixInsight, can always use the practice.

 

Im sure someone else more knowledgeable will clarify or debunk any thoughts I misstated on this.



#4 Bubbadawg

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Posted 20 January 2019 - 06:03 PM

Thanks for reply Eric. I will hopefully get out with no moon and see what I can do. Just couldnt figure why 1st image with less exposure time turned out better. I used same procedure when processing in Gimp. Ph well, I'll keep plugging away.



#5 Bubbadawg

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Posted 20 January 2019 - 06:08 PM

I suspect there may be more data in your second batch of images that just needs to be teased out via additional stretching.  On my device, the background sky still appears quite dark. 

 

Im not really knowledgeable on DSLR photography but did notice the ISO setting 1600 vs 3200 change as well. I equate this to gain on Astro cameras.  What I believe you are gaining is more dynamic range with lower setting at the cost of exposure time needing to be longer.   There is a formula involved, (square root of something Time something) Charles Bracken book, Deep Sky Image Primer explains well regarding signal to noise.  Long story short, think by reducing your ISO you would have needed more exposure time to achieve similar brightness level in the base sub exposures.

 

if you make you subs, ect available for download. I’d be happy to give the data a shot in PixInsight, can always use the practice.

 

Im sure someone else more knowledgeable will clarify or debunk any thoughts I misstated on this.

Thanks Mariner. I think I am tracking with what you are saying.

Not sure how to upload data files. I'm not that tech savvy. Let me know how and I'll do it.



#6 Kevin Ross

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Posted 20 January 2019 - 06:09 PM

Put the files on some cloud storage service, like Dropbox or One Drive, and share a link to it.

 

Oh and please post the original raw files from the camera, not the processed images.


Edited by Kevin Ross, 20 January 2019 - 06:11 PM.


#7 Stelios

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Posted 20 January 2019 - 08:43 PM

You will not get great pictures of galaxies with the moon out. I don't even bother shooting under such conditions.

 

You should take more images, longer images, and lower ISO images. Try for 30 x 180" at ISO 800 with no moon out, and you should get some beautiful results. 

 

BTW, the darks, bias and flats don't make a brighter image. Certainly they don't compensate for lower ISO. What they do:

 

Bias corrects for the noise introduced by the action of taking a picture. 

 

Darks correct for dark current noise--a background noise (particularly visible upon closeups) introduced by the camera itself and related to the length of the exposure and temperature.

 

Flats correct for vignetting and dust motes (if any). 

 

The combined effect of darks/flats/bias is to make the background smoother (lower noise), eliminate hot pixels and also get rid of variations in brightness in the corners of the image (vignetting).



#8 Bubbadawg

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Posted 20 January 2019 - 08:56 PM

Thank you Stelios! I will work on that. I guess just trying to do too much too fast. Especially when I surf the net and see where someone posts a pic and says even under a full moon they got excellent image. Thanks all for patience and taking time to explain things.


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