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Beginner Cresent Nebula help

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#1 Serial

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Posted 18 June 2021 - 12:29 PM

This is about 100 subs of 30 seconds each (the longest my unguided cg-5 can do) at 600mm with an 80mm ED refractor and my Nikon D3300.  Bortle 4, cresent moon.  DSS and Gimp. 

 

Wondering if anyone can pull more data out or if this is about as good as I'll get with this stack.  I guess it needs a lot more time but I have to drive to a location and can't stay out all night. 

 

C and C is welcome!  

 

Here's the stack.  https://drive.google...iew?usp=sharing

Attached Thumbnails

  • Cresent Nebule 2 web.jpg

Edited by Serial, 19 June 2021 - 08:21 AM.

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#2 Mike in Rancho

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Posted 19 June 2021 - 01:18 AM

Ok, you did much better at revealing the crescent in your stack than I did. tongue2.gif

 

Here's what I came up with:

 

Serials NOT Crescent.jpg

 

Maybe I just needed to stretch it more?  I didn't put any real time into this, as the data is just awful thin for the, um, faintly sea-bird shaped crescent.

 

Seriously though, my guesses would be similar to what you already said - a lot more time needed.  And then some, with unmodded DSLR on this type of target.  That forces an overstretch in processing in order to see the things you want to see, but what you end up with is broken nebulosity and clumpiness.  (I've been there myself).  Lack of guiding can compound this.  Not that your stars look bad, not at all, but with guiding you can dither which helps with mottling caused by walking noise.  You might look into some manual dithering or nudging techniques, I've seen them mentioned around here.

 

Are you also taking calibration frames?  Enough of them?

 

Anyway, if time is short, you might want to work on broadband and brighter targets for getting started in learning.  If you really want that crescent though (or even a pelican), I think it will take a multi-night effort to really build up a lot of integration time.


Edited by Mike in Rancho, 19 June 2021 - 01:20 AM.


#3 rj144

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Posted 19 June 2021 - 02:11 AM

This is about 100 subs of 30 seconds each (the longest my unguided cg-5 can do) at 600mm with an 80mm ED refractor and my Nikon D3300.  Bortle 4, cresent moon.  DSS and Gimp. 

 

Wondering if anyone can pull more data out or if this is about as good as I'll get with this stack.  I guess it needs a lot more time but I have to drive to a location and can't stay out all night. 

 

C and C is welcome!  

 

Here's the stack.  https://drive.google...iew?usp=sharing

Your link is for the Pelican Nebula I think.



#4 DeanCN

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Posted 19 June 2021 - 02:22 AM

its not NGC 6888 ... check and repost your share ?



#5 Serial

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Posted 19 June 2021 - 08:20 AM

Whoops!  Sorry. blush.gif  Here's the Crescent Stack.  https://drive.google...iew?usp=sharing


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#6 terry59

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Posted 19 June 2021 - 10:34 AM

Here is what I get....seems about right given the short subs and unmodified camera

Attached Thumbnails

  • Cresent_Nebule_Stack_6_16_21_ABE.jpg


#7 Mike in Rancho

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Posted 19 June 2021 - 01:21 PM

Now that's the crescent! laugh.gif

 

Big file.  I thought maybe it would be a drizzle, but turns out probably just the wide-flung stacking?  You might try intersection mode in the stacking and see how that works.  Ultimately I ended up cropping even deeper, because even after the initial crop I wasn't sure that I was getting the full stack in all locations.  Unfortunately I had already binned it down by then.  If I were to go at it again, I'd do that final crop from the get go to try to preserve more resolution.

 

As noted, just add more and more time, a multi-night target perhaps.  When you get in close and look at especially the smaller stars, they all seem to have somewhat of elongation to them, and all in the same vector.  Guiding will help with this of course.  I myself held off on getting a guidescope for quite a few months, but I was just throwing out too many subs and/or having to keep my exposures short in order to maintain round stars.  Sometimes a tighter kappa rejection in your stacking can help round out stars too, but not always.

 

A very busy starfield, just a lot in the sky here, so not easy to make the crescent stand out on such short total integration.  But it's there.

 

Pretty good start though what you got, considering the difficulty of red nebula with your setup.  And better than the pelican! tongue2.gif  Here's what I got with a relatively quick run through.

 

gallery_345094_15786_191677.jpg


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#8 Serial

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Posted 19 June 2021 - 05:28 PM

Now that's the crescent! laugh.gif

 

Big file.  I thought maybe it would be a drizzle, but turns out probably just the wide-flung stacking?  You might try intersection mode in the stacking and see how that works.  Ultimately I ended up cropping even deeper, because even after the initial crop I wasn't sure that I was getting the full stack in all locations.  Unfortunately I had already binned it down by then.  If I were to go at it again, I'd do that final crop from the get go to try to preserve more resolution.

 

As noted, just add more and more time, a multi-night target perhaps.  When you get in close and look at especially the smaller stars, they all seem to have somewhat of elongation to them, and all in the same vector.  Guiding will help with this of course.  I myself held off on getting a guidescope for quite a few months, but I was just throwing out too many subs and/or having to keep my exposures short in order to maintain round stars.  Sometimes a tighter kappa rejection in your stacking can help round out stars too, but not always.

 

A very busy starfield, just a lot in the sky here, so not easy to make the crescent stand out on such short total integration.  But it's there.

 

Pretty good start though what you got, considering the difficulty of red nebula with your setup.  And better than the pelican! tongue2.gif  Here's what I got with a relatively quick run through.

 

gallery_345094_15786_191677.jpg

 

Mike, this is beautiful.  Thank you so much for your thoughtful feedback.  I've been at astronomy/astrophotography for about 5 months now.  

 

Yeah, the file is big because I was sort of shooting all over the place and kept all of it in the stack.  Nice crop.  

 

My stars were certainly eggs, at best.  My lowly manual/clock drive CG-5 can't do any better.  How did you make the stars so small and faint?  I feel like they compliment the DSO really well in your edit, as opposed to overpower it.  

 

Your edit is inspiring that I might be able to create some truly beautiful pics at some point. 


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#9 Mike in Rancho

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Posted 20 June 2021 - 06:51 PM

Mike, this is beautiful.  Thank you so much for your thoughtful feedback.  I've been at astronomy/astrophotography for about 5 months now.  

 

Yeah, the file is big because I was sort of shooting all over the place and kept all of it in the stack.  Nice crop.  

 

My stars were certainly eggs, at best.  My lowly manual/clock drive CG-5 can't do any better.  How did you make the stars so small and faint?  I feel like they compliment the DSO really well in your edit, as opposed to overpower it.  

 

Your edit is inspiring that I might be able to create some truly beautiful pics at some point. 

I'm not too far ahead of you!  I goofed around (literally not much more than that) in years past every now and then, but just now coming up on a year since I started pointing the camera skyward more often and started some basic research.  But it was last fall by the time I got my mount, and then processing software, and finally the ED scope.

 

If you're having fun, enjoy the challenge, and can handle things going sideways every now and then (they just do), you'll be well on your way.  Just takes practice, experimentation, reading, and sometimes a bit of a shopping spree too. smile.gif  Oh and before the shopping, just proper expectations of what your equipment can do, and what it can't readily do, absent a lot of extra time and work.

 

There are a lot of ways to shrink, dim, or push back stars in order to enhance the prominence of a DSO target.  For your data, in Startools, I used the Shrink module and Super Structure module with settings I thought appropriate to the task.  I also went easy on the initial stretching.  If the data doesn't support it, as here, a big stretch just to see as much of the target as you can will also stretch out all the stars and unwanted noise as well.  I probably could have tried to warp the egg stars back into normal space lol, but really didn't think it was too necessary.  All is good as long as you don't lean too close to the screen and start staring at the little things. tongue2.gif

 

Another popular trick is to process starry and starless layers separately, then bring them back together afterwards.

 

For Gimp - well I'm not real sure, as I gave up on Gimp for processing pretty early on, even though I had the two main astro plugins for it (which don't compare to the plugins available for PS).  Mind the stretching, as noted.  I also think I remember one of the Youtubers - Astrofarsography - had a couple Gimp tutorials, one of which covered shrinking and/or dimming (unsure which it was) of stars.  So you might look into those techniques.




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