I have been out and about with my narrowband filters again. I have managed to make my first tri colour narrowband astrophotograph.

The image:

Heart Nebula in Ha, SII and OIII

I have taken 38x900s of hydrogen alpha (ha), 33x900s of SII and 39x900s of OIII. A total exposure time of 27.5 hours. As I keep saying in this astrophotography blog, you need to take a lot of exposure time to get a narrowband image. Making a colour narrowband image is worse.

In most narrowband targets the signal from hydrogen alpha emission dominates. OFten by an order of magnitude. Therefore we need to take huge integrations of the weaker species and then attenuate the Ha in our processing so that we end up with a balanced image.

In a few days I will procedure a monochrome result in just Ha for this region - which goes much deeper than this image.

I've found the tri-colour processing of narrowband imaging to be a steep learning curve, lots of different ways of doing things. Do we process the three channels separately and then combine in photoshop - or do we do the combine in maxim? Do we sharpen and noise reduce the channels individually, or only the final RGB image? Lots to experiment with.

Please click on the image below for the full sized image and the full details on this image.

heart nebula astro in narrowband

It is very interesting to see how the different emission species come from different parts of the nebula. The dominant Ha emission forms the main structure of the nebula, with the red SII on the "outer edge" of the nebula, which gives it the brown trimming to the edge. The central "pool" of the nebula is filled with the blue OIII emission.

It is worth mentioning that the colours represented here are somewhat artifical. Both the Ha and SII emission are in the far red of the spectrum, and the OIII in the blue, however we choose to put the Ha into the Green channel to give a balanced image. Because the eye responds best to green , we put the strongest dataset (ha) in this channel.