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Lovely fine detailed image. Thanks for the stars tutorial. Funny as I was just watching an educational DVD on how to select out the stars separately. Wodaski's book goes over a method to do this but I did not find it to work very well.
Whilst there appears to be no right or wrong in narrowband I have found in my dabblings with it and from advice from others (notably Richard Crisp who has done a lot of work in narrowband) that the red channel - S11 is where it gets hard and breaking the Ha dominance in the image is key.
My first efforts with Eta C in narrowband came out similarly with blue and green being dominant. I think this is common with most narrowband imaging. Fred could comment here.
So you have some choices:
1. Expose much more of S11 and use 2x2 binning.
2. When doing RGB combine work out various combine ratios pumping up the S11 and O111 as Ha will almost always be very dominant and overwhelm the image.
3. In the final image using Ha as a luminance layer will also add some sparkle and detail to the image.
I found I had to push the red channel with curves to bring it up and the blue/green dominance became more balanced and overall a more "traditional" Hubble narrowband look.
So one formula is:
1. Image Ha 1x1 but O111 and S11 in 2x2.
2. Use much longer subs for O111 and S11 (20-30 minutes or even longer) to get the signal to noise ratio up. Use longer total exposure times for these as well with S11 getting the most.
3. When doing your SHO combine weight S11 the highest, then O111 the next highest and Ha leave at 1.
4. Be prepared to push the red channel harder with curves to break the blue/green dominance in some images.
5. Taking shorter RGB image for the stars and installing as you have detailed in your excellent tutorial.
Another formula I personally like is:
1. Do an LRGB image.
2. Take O111 and Ha and add to the image.
3. I usually don't bother with S11 as it adds little to the final image.
So HaO111LRGB can make a very interesting image on some objects like Vela and appears to be more of a tradiitonal LRGB but with extra details enhanced. Don Goldman has done some great work in this format.
I hope this helps and I don't consider myself an expert on narrowband nor like it that much but this is what I have learnt so far.
There are some stunning narrowband images around. Ken Crawford has done a marvellous NGC3576 for example. That object looks better in narrowband than LRGB. But it also requires a largish image scale.
Greg.
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