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I Stacking images

  1. Oct 10, 2018 #1
    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?
     
  2. jcsd
  3. Oct 10, 2018 #2

    Drakkith

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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?
     
  4. Oct 10, 2018 #3
    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
     
  5. Oct 10, 2018 #4

    Drakkith

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    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.
     
  6. Oct 10, 2018 #5

    russ_watters

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    Registax can use as few as 1.
     
  7. Oct 11, 2018 #6
    IRAF is the pro Unix based software. It is very powerful but very old and command line driven.
     
  8. Oct 17, 2018 #7
  9. Oct 18, 2018 #8

    davenn

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    Yup …. I have used it for some years now … but I, like many, only do the stacking in DSS
    we do the editing in lightroom, photoshop or whatever you other fav image processing app is


    Dave
     
  10. Oct 18, 2018 #9
    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
     
  11. Oct 18, 2018 #10

    russ_watters

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    Did you do any post processing? Can you upload a sample? Often, the signal needs a lot of amplification to be visible.
     
  12. Oct 18, 2018 #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.
     
  13. Oct 18, 2018 #12

    davenn

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    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)


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


    Dave
     
  14. Oct 20, 2018 #13
    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.
     
  15. Oct 20, 2018 #14

    davenn

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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
     
  16. Oct 20, 2018 #15
    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 :((
     
  17. Oct 20, 2018 #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.
     
  18. Oct 20, 2018 #17
    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 :))
     
  19. Oct 21, 2018 #18

    Drakkith

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    Welcome to astrophotography and image processing. :wink:
     
  20. Oct 22, 2018 #19
    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
     
  21. Oct 23, 2018 #20
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