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Originally Posted by mickoking
Both images are great but I prefer the blue one on aesthetics. But what one is closer to the real colour of the Lagoon?
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What a great question, and no one I ask can give me a definitive answer. The best I've heard is "It depends....". The reasons it's hard to get an answer are many.
Nebulae emit light strongly at specific frequencies. Hydrogen H-alpha (red), H-beta and OxygenIII (blue-green), Nitrogen (blue), Sulphur, etc.. Different nebula emit light more strongly at some of these than others. The bright stars within nebulae also contribute a broadband 'white' light component that is dispersed and scattered through any surrounding gas and dust which in turn take on their own hues. All of these are on the 'transmit' side of the equation.
On the 'receiver' part of the equation our cameras each respond to the light in different ways. A stock Canon 350D has its peak sensitivity in the green part of the spectrum and is much more sensitive to blue-green light than it is to the wavelength associated with H-alpha. A Hutech modified Canon 350D is five times more sensitive to H-alpha than a stock camera and has H-alpha response that gets closer to its response for blue-green. Astronomical CCD cameras on the other hand tend to have their peak sensitivity skewed more to H-alpha since most emission nebula emit very strongly at the H-alpha wavelength.
Combine the different strengths of emission lines on the 'transmit' side of the equation with the different responses to those emission lines on the 'receive' side of the question and its very puzzling. Some photos you'll see include an Infra-red or even ultraviolet component neither of which we can see but which combine to create "color" in an image.
So even if there was a standard and known range of colors being emitted the different types of camera would record the color balance differently.
The question of what is the 'real' color is further complicated because our eyes are poor receivers of H-alpha light especially in near-darkness. A stock Canon 350D therefore (because that's the way its been designed) responds to the different frequencies of light in an approximation to how our eye responds (but to daylight!). The low-light spectral response of the eye is different to the bright-light response.
It all gets very confusing, and I find the whole issue of choosing a color balance for imaging very vexing. The closest I've come to a plan to nail exact visual color is to locate what's called G2V main sequence stars (white like our sun [it is not yellow]) and use these as a color reference but it just adds more work, ho hum...
Combine all of the above with skyglow adding a wash of unwanted color into the image and aaaarghh.....
Usually I just set the black point on each color channel to balance the histogram peaks on each color, just accepting that the camera recorded what it recorded and be done with it....
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