NGC6164 - The Dragon's Egg

In my last update I mentioned the ‘Egg’ in the bottom right corner of my image of NGC6188 and how it would make a good target for the Megalens. Well, my chance came around a lot sooner than I expected.

I also think it’s fair to say that this image will be the last from the Megalens - it’s just not cut out for astro work. I’ll be saving my pennies from here on for an upgrade / companion to the SW72ED. Right now, I have my eye on the new Apertura CarbonStar 150 reflector.

Anyway, back to this image - I forgot that the moon was only one night past it’s maximum, and was not too far away from the ‘Egg’. Even with the light shield on the Megalens fully extended, there was a lot of spill-over light and almost all the light frames were of high noise and low contrast. A much longer light shield would have helped, but I didn’t have one, so not a lot I can do there.

My first attempt at processing the data was… in a word, appalling. Massive amounts of noise, horrible patterns in the background, and a totally over-blown centre. I’ll not mention the shape of the stars - initially they were more like obese ‘V’ shapes than circles. (I’m so thankful that Siril has the Star Resynthesis capability!)

The second attempt went a lot better - I sifted out the worst of the light frames before stacking them with my usual workflow in Siril. This time I neglected to use the GHS and went for the auto-stretch via the Histogram Stretch module. I suspect that if I spent a good amount of time carefully stretching the image via GHS, then I’d have a better image again, but I wasn’t in the mood to walk that road.

I then fed the stretched image into Graxpert and hit the ‘GO’ button. Even with the non-round stars, it was much better image than I had obtained in attempt one. So I fed the Graxperted file into Siril for a hit of starnet++ (followed by the Star Resynthesis to get the round stars back again).

One thing about the Star Resynthesis - it says you should do this to linear (unstretched) data. However I’ve been noticing some awful artefacts (speckles and bright pixels) around the brighter stars. This time I just threw the stretched file at the Star Resynthesis module. To my surprise the output was almost perfect - round stars and NO artefacts!

There’s only so much you can do with below-average data, so the image below is as good as I’m going to get. A few more hours of imaging in better conditions would really make a great image. I just need to be patient and wait for another clear night with less moon.

Image data:

  • Gain: 100
  • Offset: 10
  • Temperature: 0 degrees C
  • Exposure: 120 seconds
  • Frames: 59 Lights, 25 Darks (2 hours integration in total)
  • Filter: L-Enhance (Ha + Oiii dual-narrowband)

Equipment: Megalens @ 1000mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / Kstars/Ekos

NGC6164 - The Dragon's Egg

If you open the image in a new tab (at a larger size) you’ll be able to see the very faint ‘outer bubble’ of gas and dust to the top-left of the nebula. There is a matching one to the lower right, but it’s not visible in my image.