M20 - The Trifid Nebula

The image that nearly never was…

I started out wanting to capture the Helix Nebula (NGC7293) as it’s big and bright at the moment. Nope, stopped by guiding issues - my software decided to try and guide on a hot-pixel in the guide camera. Something I’ve never had happen before. So I did the usual things of trying different camera settings before giving up.

Roll forward a few weeks and we (finally) got another clear night. So I tried the Helix again. Nope, still no guiding. Luckily, I had researched a few back-up targets to try, so I moved over to M20.

Again, I had guiding issues, and the software still tried to guide on a hot pixel. I managed to get around that, and kicked off the imaging sequence, only to find that after each dither operation the guiding would fail spectacularly. The software would eventually work out the guiding was rubbish and re-calibrate itself to take the next 10 frames before doing it all over again.

Since then I have deleted and recreated the library of dark images for the guide camera, so hopefully this will stop the thing from trying to guide on a hot pixel. I also need to have a look at the mount, as it appears to have developed at least one tight spot that makes it more difficult to rotate on the RA axis. At least I know how to take it apart and check the bearings and tolerances. Maybe I can get to that on the weekend? Oh, and check the backlash on the worm drive, it might be binding…

So anyway, I have an image. Given the issues I had in capturing the data, I’m not overly disappointed with how it turned out. Now to drop the L-Enhance filter into it and get more of those lovely Ha photons.

Image data:

  • Gain: 100
  • Offset: 10
  • Temperature: 0 degrees C
  • Exposure: 30 seconds
  • Frames: 170 Lights, 25 Darks, 34 each of Flats and DarkFlats (85 minutes integration in total)
  • Filter: None
  • Processed with SiriL (stacking, pre-processing and star removal) then finished in Affinity Photo v2

Equipment: SW72ED @ 420mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / Kstars/Ekos

M20 - The Trifid Nebula

Update - More photons captured

We had another clear night, so I determined to grab the Ha data (as I said above) to fill out the image of M20.

I still had problems with the guiding, but was able to implement a work around. I have since taken the mount apart and re-greased the bearings (one was very dry) on the RA axis. The mount now moves a lot more freely, so hopefully that will be the end of the guiding problems…

There is a very small amount of backlash in the worm-drive. However, the difference between the RA axis rotating freely with the backlash and binding the two gears was a tiny turn of the adjustment screw. So I’ve left it with the backlash and hope that the guiding will be able to work around it.

Image data:

  • Gain: 100
  • Offset: 10
  • Temperature: 0 degrees C
  • Exposure: 120 seconds
  • Frames: 60 Lights, 25 Darks, 50 each of Flats and DarkFlats (120 minutes integration in total)
  • Filter: L-Enhance

I combined the data from the two sessions together to give the new image. See how the additional Ha data really brings out the red of the reflection nebula.

M20 - The Trifid Nebula