Stacking images

  • #1
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Hey!

So, I took images of NGC 7741 at school using CCD Soft. The field view looked exactly how I would expect when aligning to my galaxy, so I'm almost 100% my galaxy will show up once I stack my images ( I took a set of 20 with 1min exposure). I tried to check by stacking through PixInsight, however, there are unfortunately only around 3 stars that showed up on my images, PixInsight says you need 6 in order to stack.

Should I just go through with the assumption that my galaxy is there (although I can't see it) and start my data reduction and stack the images through IRAF?
Is there another way I can stack?
 

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  • #2
Drakkith
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Is there another way I can stack?
I'm not familiar with your software, but there is other software that requires fewer stars to stack or lets you manually stack.

Should I just go through with the assumption that my galaxy is there (although I can't see it) and start my data reduction and stack the images through IRAF?
What is IRAF?
 
  • #3
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I'm not familiar with your software, but there is other software that requires fewer stars to stack or lets you manually stack.



What is IRAF?
There’s software that uses fewer stars? Do you happen to know any?

we do our data reduction stuff through Xming/PuTty and it involves doing stuff in an IRAF and a Linux terminal.

I don’t really know how to explain it :// I’m in second year so don’t have extensive experience with data reduction
 
  • #4
Drakkith
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There’s software that uses fewer stars? Do you happen to know any?
I use AIP4Win, but it's not free. CCDOPS will let you manually stack, but it's rather tedious for anything but a handful of images.
You can probably download a trial version of MaxIm DL Pro and use that.
 
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  • #5
russ_watters
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Registax can use as few as 1.
 
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  • #6
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IRAF is the pro Unix based software. It is very powerful but very old and command line driven.
 
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  • #8
davenn
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  • #9
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Try DeepSkyStacker (64 bit). Free and very versatile.

http://deepskystacker.free.fr/english/download.htm

BC
This was helpful! Tried stacking, didn’t see the galaxy :(( there was a light leak when we were take photos of my galaxy(+11.25 mag) guess I’m using my friend’s images for data reduction, he didn’t have light leaks when he took the images of the galaxy later in the night:((

Although two professors told me that my field of view was perfectly fine and my galaxy SHOULD be there. Gosh darn it
 
  • #10
russ_watters
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This was helpful! Tried stacking, didn’t see the galaxy :(( there was a light leak when we were take photos of my galaxy(+11.25 mag) guess I’m using my friend’s images for data reduction, he didn’t have light leaks when he took the images of the galaxy later in the night:((

Although two professors told me that my field of view was perfectly fine and my galaxy SHOULD be there. Gosh darn it
Did you do any post processing? Can you upload a sample? Often, the signal needs a lot of amplification to be visible.
 
  • #11
Do you use any plate solving programs, like Astrotortilla? This will let you precisely place your subs by matching your field with with referenced images.
 
  • #12
davenn
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Tried stacking, didn’t see the galaxy :((
in DSS ?

As @russ_watters hinted at, even after stacking in DSS, you will have to do significant post processing to bring out the object
Only with bright objects will you see anything of them after doing the stacking ( but before processing)


there was a light leak when we were take photos of my galaxy(+11.25 mag)
well that would probably destroy any faint objects and M11 or more is very faint


Dave
 
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  • #13
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in DSS ?


well that would probably destroy any faint objects and M11 or more is very faint


Dave
But this should show up after I do my reduction right? I’m hoping the light leak would somewhat be subtracted but idk. I’m worried now, definitely don’t want to have to go back and take images again.
 
  • #14
davenn
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I’m hoping the light leak would somewhat be subtracted but idk
if the light leak is on every frame, then no it wont be subtracted

if it is only on a couple of images, then remove those images from the ones to be stacked
 
  • #15
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if the light leak is on every frame, then no it wont be subtracted

if it is only on a couple of images, then remove those images from the ones to be stacked
Ah darn, looks like I’m retaking my images then ;-; (or not, my prof knows what happened and he said he’ll let me use my partner’s images for the reduction instead)

Do want my own set of images though, the galaxy is gorgeous


EDIT: We did move the field of view as far away from the light leak as possible though (the field of view matched exactly so all of the galaxy is supposed to be in the darker area) guess I’m still screwed :((
 
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  • #16
First, are you properly 'stretching' your image? Images can sometimes be much darker than regular photos. In Pixinsight, use the 'nuke' button for auto screen transfer function.
Second, if you can't see the object after 'stretching' your image on a single frame, than stacking is not going to make it magically appear. Stacking will reduce noise.
Third, proper calibration images (bias, dark and flat) can help fix light leaks - to some extent.
 
  • #17
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First, are you properly 'stretching' your image? Images can sometimes be much darker than regular photos. In Pixinsight, use the 'nuke' button for auto screen transfer function.
Second, if you can't see the object after 'stretching' your image on a single frame, than stacking is not going to make it magically appear. Stacking will reduce noise.
Third, proper calibration images (bias, dark and flat) can help fix light leaks - to some extent.
The images I saved and worked with were black for some reason so I did stretch them, after stretching them, they looked like what I saw on the computer while using the CCD(my galaxy wasn’t there when I was taking images with the CCD - but my prof had said that we shouldn’t expect them to show up while we’re taking images, only after reducing)

But now there’s this amazing light leak I also need to deal with :))
 
  • #18
Drakkith
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But now there’s this amazing light leak I also need to deal with :))
Welcome to astrophotography and image processing. :wink:
 
  • #19
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PIxinsight: in Star alignment go to Star Detection and try these settings:- Detection scales try 8
Log Sensitivity try -3
All the rest in star detection leave at default
 
  • #20

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