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B Are colors in astro photos 'real'?

  1. Aug 19, 2016 #1
    There are lots of amazing photographs of nebula around. The colors contribute greatly to their grandeur.
    But if we were able to get near enough to a nebula to see it with the naked eye would it possess the colors we see in published photographs taken by telescopes? Or are the colors in astro photos in some way artificial or exaggerated?

    Similarly I note that some astro photos show effects similar to a photographers starlight filter - have these shafts of light been added for dramatic effect in digital post-processing (eg photoshop) or are they genuine artifacts, eg of the telescope optics?
     
    Last edited: Aug 19, 2016
  2. jcsd
  3. Aug 19, 2016 #2

    Bandersnatch

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    This depends greatly on the photo you're looking at, but in general the colours tend to be real - in the sense that they're not artificially added or altered (but not always, specifically in case of photos made in non-visible light, where the input has to be translated into visible output).
    However, the exposure times are long, which means that you'll never see with a human eye the colours that you see on the photos. There's just not enough light reaching your unaided eye to activate the colour-sensitive cones, even when standing smack in the middle of a galaxy - best you can see of the Milky Way is a fuzzy grey band (its grey because rods in the eye are more sensitive to light, but perceive everything in the shades of grey).

    Those are diffraction spikes due to telescope construction. Mostly caused by the struts holding the secondary mirror in e.g. Newtonian-type telescopes.
     
  4. Aug 19, 2016 #3
  5. Aug 20, 2016 #4
    Bandersnatch - thanks for that very informative reply, answered my questions perfectly.
    newjerseyrunner - thanks for the link, very useful too.

    Cheers
     
  6. Aug 20, 2016 #5

    phinds

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    There was a long thread on exactly that some time back if you feel like a forum search
     
  7. Aug 21, 2016 #6

    davenn

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    If they are board spectrum visible light images, then they are likely true colour
    eg this photo of the great Orion Nebula of mine .....

    upload_2016-8-21_18-7-18.png


    narrow band imaging in various wavelengths tend to be false colour eg this IR image of the Orion Nebula .....

    m42-43_2m.jpg


    Dave
     
  8. Aug 21, 2016 #7
    It's generally a good idea to inform yourself about the whole range of the electromagnetic spectrum that telescopes can capture, which is much wider than what a human eye can see. Anything above or below the range of visible light wavelength (400-780 nanometres) is invisible to the naked eye.

    Many space photographs employ false colors in IR or UV photos. We wouldn't be able to see those objects through the naked eye.

    It's also important to take into account how many light/years they are away from us. Today, the furthest ones don't look like the light that reaches us or don't exist anymore.
     
  9. Aug 21, 2016 #8

    1oldman2

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    :thumbup::smile: How many stacks is this image made from ?
     
  10. Aug 21, 2016 #9

    russ_watters

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    For one of my favorite photos I added the diffraction spikes by adding wires across the front of my scope (which doesn't have struts). It is basically a natural color image (I used hydrogen alpha for red).

    Horsehead-HaRGB.jpg
     
    Last edited: Aug 21, 2016
  11. Aug 21, 2016 #10

    davenn

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    15 from memory
     
  12. Aug 21, 2016 #11

    davenn

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    sweet shot, Russ ..... I have imaged that region but not as well as you
     
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