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Saturday, May 29, 2010

M16 experiment, narrow band with a Broad band luminance.

HST-palette colors with a Broad band luminance. RGB-Stars.
Red=S-II, Green=H-a and Blue=O-III

Natural color narrow band composition with a Broad band luminance. RGB-Stars.
Red=70%Ha+30%S-II, Green=O-III and Blue=70%O-III+30%H-alpha.

In this experimental image, I have tested the method to use a clear filter luminance with a narrow band color. This is (only?*) scientifically correct method to use a luminance image with a narrow band colors, since a broad band luminance contains all the wave lengths used for color information.

I don't usually like to mix colors from a different imaging methods, like pure RGB and narrow band. In this case I have used RGB, real color, stars with an emission line image.

Some astro imagers tend to use H-alpha channel as a luminance, due the higher details and better S/N than any other channel has. Even though the visual appearance might look better, other channels, O-III and S-II, has no information in H-a luminance and all details in there are lost!

(*I have to point out, I use H-a  luminance with a many NB images but H-a is boosted with all the information in O-III and S-II channels used. I call this method "Tone Mapping". Step by step instructions can be found here: )

The original narrow band image, with technical details, of  M16 can be found here:

Technical details
Imaged with a Northern Galactic members remote telescope in Australia,

16" RCOS ja Apogee U9000 camera. 
LRGB combo.
H-alpha 5x1200s, O-III 2x1200s, S-II 2x1200s . Dark and Flat calibrated.
Broad band luminance 15x300s.
RGB-colors Red 2x300s, Green 2x300s and Blue 2x300s.
Raw data is shared with Petri Kehusmaa and J-P Metsavainio

Processing workflow:
Image acquisition, MaxiDL
Stacked and calibrated in CCDStack.
Deconvolution with a CCDSharp, 30 iterations.
Levels, curves and color combine in PS CS3.

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