M17 - The Swan Nebula

This object is also known as the Omega Nebula. It's another one that's been sitting on my hard drive for a couple of years waiting to be processed.

When I went through the data, I discovered that back when I captured it, I calibrated the subs in CCDStack, but never integrated it or made master frames. Up until very recently, my workflow has been to use CCDStack for everything up through integration, and then move to PixInsight. Since this data was never integrated, it gave me a good opportunity to do it in PI. And since it was somewhat under sampled due to largish pixels and short focal length, it's the first image that I have drizzle integrated.

Another thing that made this one a bit different to process, is that there are Ha emissions just about everywhere in the frame. My first cut at processing was to boost the faint areas a lot and also stretch the color data so as to preserve as much saturation as possible prior to blending it with the luminance.

There were two problems with that strategy. First, when I compressed the histogram enough to bring out all of the luminosity, I had flattened the bright "swan" shape enough that it was not immediately recognizable. My wife was a bit disappointed with this, so I made a conscious decision to redo it and maintain its namesake feature. The second thing is that I had preserved so much saturation, that it had a quite unnatural appearance, and also had areas that were red-clipped. Toning down the saturation helped not just with the overall appearance, but allowing the swan shape to desaturate to pink, helped to preserve it.

Equipment used was as follows:

Stellarvue SV80ST at F/6

SBIG ST-10XME with Astrodon Gen1 LRGB filters

Astro-Physics AP1600GTO-CP3

The exposures were 49x60 luminance, 35x60 red, 35x60 green and 44x60 blue. All were taken on the night of 6/30/16 at Golden State Star Party.