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Ahh yes, the colour balancing can be a hairy issue. My old 300D did just that, showing even known to be fairly red nebulae such as Eta carina as a bluish pink, and the tarantula a strongly blue. Photoncollector (Paul) showed me that using Curves in photoshop on the red channel could bring out more red without making too much of an overall red cast. Also, I found out that by using a nebula filter like the Baader UHCS, Lumicon Deep sky or equivalent, and using high ISO to get around the filter factor, a good deal more red would come through.
The software I use, Iris, has a commandline function called "white". I draw a small box on a dark area of sky with no stars inside, then enter "white". This tells Iris to balance the image to get a neutral grey on the sky background.
The Human eye, however, sees astronomical nebulae more like an unmodded DSLR. As an unmodded camera looses HA sensitivity dur to the IR cut filter, the human eye looses HA sensitivity because the Rod cells in the retina cannot detect low levels of HA light, and the more sensitive rod cells cannot either, only shorter wavelenghts, only very bright nebulae in big scopes such as M42 in a 20 inch dob will show much red. Some peoples eyes are better than others perhaps, but I struggle to ever see any red with my 10 inch scope and low power eyepiece.
With my modded DSLR, using a nebula filter brings out plenty of red, so much so that I need to be careful not to make it too intense.
here are some raw images processed only with canon's own Digital Camera professional software to show us the images without any external colourbalancing or any other adjustments done, they are "as shot" Similar shots with my old 300D would show the sky background as bluish, even with the filter in place.
Ive read that the one true way to colour balance, is to take a picture of a white card, preferably an official photographers colour chart, using the exact filterset that you will use to take astro images with, take note of the adjustments deeded to render the white card as white, then apply the same settings to the astro images. I might see about trying that out myself, take a pic of something I know to be white, in midday sunlight, run the image through Iris, and take note of the red-blue-green adjustments in order to get it looking white. Will be an interesting exercise. Another way would be to take a short exposure of a deliberately out of focus non saturated star of spectral type G2 (same as the Sun) and balance that as white.
Scott
EDIT: I should also say that turning OFF the Automatic White balance in the SLR camera might be a good idia too, and set it to Daylight instead, although with Iris, as it does its own debayering, the AWB might not matter
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