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Lots of stars in deep space objects

astrophotography beginner imaging
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#1 feygan

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Posted 18 March 2019 - 06:04 PM

Hey guys,

 

I was wondering, why do some pictures of deep space objects have lots of stars in them, but some of them don't? Is this done in post-process or are there some hardware things involved (like filters, integration time, lens type, etc.)

 

Example: 

https://www.astrobin.com/395925/ (lots of stars)

https://www.astrobin.com/340095/ (fewer stars)

 

Thanks!

 

PS:  I hope I posted this in the correct category smile.gif


Edited by feygan, 18 March 2019 - 06:21 PM.


#2 gene 4181

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Posted 18 March 2019 - 06:19 PM

  2 nd link isn't working  , 



#3 fmeschia

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Posted 18 March 2019 - 06:22 PM

Post processing, but your pictures also show the difference between RGB broadband imaging and H-alpha narrowband imaging.

Francesco


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#4 feygan

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Posted 18 March 2019 - 06:32 PM

Post processing, but your pictures also show the difference between RGB broadband imaging and H-alpha narrowband imaging.

Francesco

Now that you mention it, almost all of the "lots of stars" category images are in broadband.. 

 

If I understand correctly, with narrow-band filters you get something like this (https://www.astrobin.com/325970/) and without like this (https://www.astrobin.com/395213/)?



#5 bobzeq25

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Posted 18 March 2019 - 06:37 PM

In your examples, it's processing.  Too many stars tend to detract from the main target.  So people often reduce them in processing.  I do, to some degree, in most of my images.

 

The Rosette is a great example.  It's essentially right in the Milky Way, so there's a ton of stars.  The image with fewer stars has had a fairly drastic amount of star reduction applied.  The one with many stars, no star reduction at all.

 

Targets that are far from the plane of the Milky Way have many fewer stars.  They definitely need less star reduction, maybe none at all.  The galaxies around the Big Dipper are a fine example.

 

The broadband/narrowband thing comes into it, but the above things are more important.


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#6 Stephen Kennedy

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Posted 18 March 2019 - 07:06 PM

In the first picture with the 71mm refractor you  had (9/.7) = 12.85 times as much integration time as the second image  With the C-14 you had (355/71)^2 = 25 times as much light gathering capacity so you should have actually had more stars in the second image.  However, the Moon produced a lot of light that night and the C-14 may have picked up a lot more of that light blotting out many of the fainter stars.  The C-14 also has a narrower FOV so there were fewer stars that could have been imaged with it.


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#7 vio

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Posted 18 March 2019 - 08:32 PM

Integration time ... 9hrs vs 0.7hrs.


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