M31 White Balance Issue?

[old_eyes]

So after a couple of months with me never being at home when there were clear skies. Last night looked good. Moon rise was not until midnight so I could get some decent time in before the moonlight started to wash things out. I wanted to try out my secondhand Canon 200mm L on my 1000D so figured a nice widefield object like M31 would be good.

Unfortunately, in the gap since my last imaging session, my son had borrowed/reclaimed (there is some debate about who owns it) the netbook I use for imaging. So I had to go for a backup old laptop. Unfortunately it only has 2 USB ports. I need three for guiding with PhD, so I needed to use a hub. But it was dead. Aaarghh!

So plan B was some short exposures unguided and keep my fingers crossed that the drift wasn't too bad.

The attached image was 2 hours of 180 sec exposures at ISO 800.

Now the problem I had was the colour cast. I had also fitted a clip-in CLS filter, and the stacked images from DSS were a bright blue instead of the strong red cast I was familiar with with the DSLR. OK I thought background neutralisation and gradient correction in PixInsight should deal with that. Got a dark background, but M31 was very blue and a lot of the stars seemed very red. Colour calibration did not fix it. In the end, this image was created by sending the file to PS and tweaking the individual colours to tone down the blue cast to M31.

So what should I have done? I think I should have done something to the white balance to account for the filter, but what?

Any advice gratefully received.

old_eyes

[Jannis]

I have no experience with that filter, yet at least, so i can't answer if that's what gives a strange result.

But on the final picture, i think it simply just have too much green and a bit too much red in it (is your camera modded?). White balance should normally fix some of this, but i don't think it would fix it all.

By reducing the green and some red in PS i think it looks really good though You'll loose come overall colors though, but you'll keep all the details and get a more natural look.

Did you shoot in raw? If you did, you shuold be able to change the white balance afterwards, so you shuoldn't normally have to worry about the white balance while shooting. Weird if it's the CLS filter that messes it up though, as i thought DSS processed all channels seretatly anyway and you can adjust it in the final stacked image?

[old_eyes]

So far I have just taken what DSS produces from the RAW files and started there. Maybe I need to look at some of the DSS parameters. I notice that there is a per channel background calibration and also an RGB background calibration option. Have just accepted defaults.

Any DSS gurus know whether I should try and fix the problem in DSS?

old_eyes

[blinky]

There is a setting in DSS that says something like 'Reset all white balances' thats what you want to choose.

[old_eyes]

There is a setting in DSS that says something like 'Reset all white balances' thats what you want to choose.

Thanks Blinky, I'll give that a shot.

I went back to teh autosaved FITS file from DSS, and found there was a significant shift between the peaks of the three channels. I aligned them and saved with adjustments embedded, and it was much better. Still a lot of red in the fainter stars (if indeed they are stars!).

old_eyes