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Hi Greg,
As I wasn't at AAIC, I can't really comment on how to do it, but I might question why you would want to.
I suppose that the theory is that summing the RGB data will give you a "false luminance" image. This is OK in theory, but in practice it makes some assumptions.
Firstly, and you mention it in your question, you have yo shoot your RGB subs at 1x1 binning, which effectively lengthens the time required to acquire the RGB subs vs, say binning 2x2. If you don't do this, then the recombination of that data will reduce some of the hard fought resolution in the L image. So given that you will have to shoot for at least twice as long, probably more to get the same RGB data, why don't you shoot RGB binned and then spend the extra time on L? An example would probably help. Take, for instance, a typical LRGB data acquisition sequence, this may be 4 hours L, followed by 30 minutes of each of RGB binned 2x2, total time taken is 5.5 hours. Now you want to shoot your RGB at 1x1, which will require at least an hour each to achieve the same depth of image, this leaves 2.5 hours for L, the recombination of the RGB data can only add back in an hour of L, so you end up with 30 minutes less luminance exposure.
You would also have to be careful when you took your RGB images, as they now contribute to the resolution of the L image, so all subs now have to be taken whilst the target is high in the sky, this shorten the period you can use to image.
Cheers
Stuart
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