[rustigsmed (Russell)]

Hi Peter,

Whenever a Narrowband filter is being used; the usual purpose is to enhance that particular signal in the image being created.

Take a hubble image, all the channels are not equal, with so much hydrogen it dwarfs the signal of the Sulfur and Oxygen. If you blended them 'normally' the image would be totally green just showing the Hydrogen. The idea is to demonstrate the three emission lines by boosting the weaker channels and creating a colour palette which helps to distinguish where the sulfur and oxygen are, as well as the hydrogen. (otherwise why bother collecting S2 and O3? - a mono Ha will do the job)

If people are adding Ha to a OSC image, it is generally to boost the Ha signal. You are able to go deeper more easily and promote the hydrogen that actually exists there and blend it in with a OSC image.

1st image below is ngc 6164 gone deep with a dslr - notice no O3 shell.

2nd Image then blended with O3 data (from the dslr and an o3 filter in front) - just checked and it was 3 hours of Oxygen data added.

that blue wasn't showing up before - and i think a good example of how narrow band filters can enhance essentially predominant RGB image.

So in some sense it is more real as it is showing what is actually there, but it is less real in terms of the image's dynamic range.

Cheers


rusty