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A fabulous Ha image there Chris.
I find this procedure works well with Ha (there are other methods this is one).
1. Do your RGB or LRGB image as normal. Register the Ha along with the LRGB so they are all aligned. You can align in Photoshop but its a pain and hard to do precisely.
2. Process the Ha by itself, levels,curves, shadows/highlights, selective sharpening etc. I would suggest making a duplicate layer of the Ha and set the top layer to soft light to increase contrast and use the opacity slider to suit. This reduces the background noise as well which will help later. Even an S shaped curve to increase the highlights but suppress the noisy background. Again later on that noisy background can mean red noise in your final image if there is no LRGB data in the same pixel. Save it as a tiff.
3. In Photoshop after you have finished the LRGB image create a 2 new layers and copy and paste the Ha into them. If you shot the Ha at 2x2 binning then resize it to match.
4. Set the blending mode to lighten on both.
5. On the first layer Click on channels and holdng down control click on green and blue channels and they go blue.
6. Control A (to select) then control delete to delete. Now you are left with only the red channel. Name that channel Ha as red
7. Use curves to boost. In lighten mode only the pixels that are lighter than the main image show through. So if you don't boost with curves generally not much comes through. So boost to taste. I sometimes make a duplicate layer and set it to saturate blending mode to boost the red if needed or simply make a duplicate layer of the Ha as red layer after that layer is boosted with curves but you want more. Slide the opacity slider to suit.
8. On the 2n layer do the above but leave the blue channel and delete green and red. I set the opacity on this level to suit but usually only about 10% to 15%. It creates the H beta colour which is magenta/blue.
I also sometimes make a layer mask of the stars so that the Ha does not affect the stars. You can attach that to the Ha as red and Ha as blue layers.
This is the same really in effect as adding Ha into the red channel and saving it as a blend but you have much more control and can change it to suit.
I also find running a noise program such as Noise Ninja is helpful on the Ha image as it tends to be noisier than LRGB images.
I also have tended over the years to keep Ha in check as it easily overwhelms an image and a pleasing image usually has a more equal blend of colours rather than just one, in this case red. So I prefer it to be more of an enhancement and slightly subtle is better than too heavy.
Some add Ha as luminance to sharpen details but you will find it creates salmon colours easily and washes out RGB colours rapidly and for very little gain. If you do add it you simply create another layer and set it to luminosity blend mode and adjust the opacity to suit. Sometimes it adds a bit of detail otherwise lost as RGB is not that great for showing sharp details.
The above is one way. Adam Block details doing Ha on his tutorials and its rather complex. I suppose you would get used to it and I am used to the above which is what Tony Hallas uses and I was using it like that before I saw his tutorials. Lighten mode is the key. Keeping the Ha background out of the image can also be important as it can add a lot fo background red noise to your image or pollute star colours. Lighten tends to prevent it from attacking stars as the RGB stars are brighter than the red Ha ones.
Greg.
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