[avandonk]

The real problem here folks is that a DSLR is designed to give an image that closely represents the 'average' human eye's spectral sensitivity to any object illuminated by daylight. There is an adjustment for artificial light by allowing for colour balance or by auto white balance and other more complicated methods. But this is marginal compared to astro images.

We barely perceive H Alpha and so a unmodded DSLR does not either. I think that is what Peter was trying to point out. Hands up those who did not know that? Ok.

David Malin pioneered careful use of RGB filters with black and white film and then by a colour process which was the opposite of colour separation as in movie film as in the earliest colour movies. He used to put together 'colour' images of many nebs etc.

The problem has always been H Alpha, what colour is it? As only our scotopic (night) vision barely has a chance to perceive it and even then it is in black and white or grey tones!

The argument is basically about assigning what colour that the parts of the EM spectrum we can't perceive.

I personally like a 'normal' colour assignment to various spectral emission lines as in O3, Hb, SiII, and Ha.

Where the problem really is that modern CCD's with no filtration are really good at a far wider spectral sensitivity than the human eye. If you could buy a DSLR without a Bayer Matrix Filter and the filter in front of the sensor end of argument. Then just treat like the DSLR as an astro CCD. Unfortunately this is not the case. So we make do with the so called shortcomings because of the cost factor. One good thing is that the Bayer Matrix filters are essentially transparent to HA and IR, this is more correct for the 'red' Bayer filters.

Colour balance has no relevance in astro imaging as the spectral width of the incoming light from stellar nebs etc is far greater even accounting for atmospheric absorption and scattering than our spectral perception.

To me it is a non issue. For one simple reason. We can record a signal and then produce an image from it. Do we throw away any signal that we cannot normally see? No just incorporate it into the final image. I do not care if it looks too red!

Bert