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False Colour Newbie Questions


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Right...have now ordered the filter wheel to go with my CCD and am now in a position (or wil be when it gets delviered) to start looking at getting some data seriously.

At present have a 7nm Ha filter, an O-III filter and a UHC Booster filter.  Am planning on imaging with these and the using the UHC as a L as will be broadband(ish)

When it comes to combining these at post-processing, how will I map these?  Am guessing Ha will go to red, but will O-III go to green and then L to blue?

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I don't see the UHC filter as bringing anything to the party. Broadband stars are much bigger than NB stars so you'd throw away much of the charm of NB imaging by using a BB filter as luminance. The BB filter will also have a fraction of the contrast of the Ha so, again, you'd be watering down the result.

When I add Ha and OIII to RGB I've developed a way of seeing what I'm doing in real time. This could be adapted to bicolour imaging, I think, but I haven't tried it. It would involve making a three layer stack in Ps.

Top        Ha                    Blend mode Luminosity

Mid         Ha OIII Ha        Blend mode normal

Bottom    Ha OIII OIII     

I'd start by switching off the top layer's visibility and vary the opacity slider in the middle layer to decide on the best balance between Ha and OIII in the blue channel. The nice thing abut this is that you can see an instant result as the percentage varies. I'd then try bringing up the Ha as luminance and adjust the saturation of the other two layers as I did so. But, as I say, I haven't tried this recipe, just one a little like it.

Olly

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