Custom White Balance - yes or no?

[glend (Glen)]

First, I have done a search here and on the web and there seems to be arguments for CWB and against. The camera is a Canon 450D, full spectrum modified, and peltier cooled, and I generally run with a Baader uv/IR cutoff filter on the front. The camera is still set on AWB, and of course I get a lot of red seemingly everywhere I point it in the night sky.
Now some say, don't worry about it, just fix it in post-preocessing with auto colour correction (depending on app used of course).
Others say, shoot a grey card, in daylight and use that to create a custom while balance. But to my mind that is just doing a custom balance for daylight and maybe useless at night.
So how do I do a custom while balance for the night sky (usual targets are DSOs, nebs, etc)? Or am I wasting my time and should just fix it in processing?

[RB (Andrew)]

AWB is your worst choice.
This is because all your subs are at the mercy of the camera deciding which WB to set each one (there could be a difference between subs).

Your going to adjust colour correction in post anyway and you should be shooting RAW so I just set it to daylight so that each sub is the same WB on the preview screen just so that when I preview each sub, they're all the same colour balance.

CWB only matters if you're shooting jpg only.
In jpg the CWB is applied to each sub and you have to process this out.

So shoot in RAW and just set to daylight for convenience.

RB

[Camelopardalis (Dunk)]

Yeah so long as you're shooting raws, the colour balance setting is irrelevant and you'll have to balance it in processing.

I've recently began tackling this using an inexact and crude method, but basically I pick a dark patch on the image to set the grey point and it gets it in the ball park. The red histogram might need dragging down a bit still, but you'll be able to see that. Yellow stars become yellow again and blue stars become blueish.

I looked at the challenge of calibrating using G2V stars and my skills aren't up to it yet

The grey card is another method I read about, but I haven't tried getting hold of one. It seems it would give you a fairly accurate profile for correcting whatever images you take.

Ultimately though you are going to end up with a lot more red signal in your images because the camera has opened its eyes to it. I've only tried a few test shots on obvious nebulous areas and was really surprised at how quickly it captures the nebulosity, hope the weather cheers up a bit so I can start capturing some real data soon.

[killswitch (Edison)]

I just manually set my WB to around 4000k. It doesnt really matter if you shoot raw but i just prefer the previews to be uniform and closer to a neutral star colour.

[glend (Glen)]

Thanks guys. Yes I shoot in RAW. I'll try setting it for daylight first. I did expect a lot of red and that's ok as there is a lot of Ha out there I was missing. I will play with the RGB in processing and see how I go. I have read that Nebulosity will auto correct the colour but have not tried that yet.