A Portion of IC 1318

IC 1318 has a couple of other names. It’s also known as the Sadr Region and the Gamma Cygni Nebula. Sadr and Gamma Cygni are both names for the bright star at the upper right of the frame.

Sadr is the star at the intersection of the lines forming the “t” shape in the constellation Cygnus. It’s a very bright star and easily visible but the nebula, though large, is quite faint. It has a very low surface brightness. But though it is faint, it is quite large in our sky taking up a couple of degrees on all sides of Sadr. This is just a fraction of the entire nebula.

The nebula is about 1,500 light years away while Sadr is about 1,800 light years away. In the image the star seems to be in front of the nebula but that must be an optical illusion.

This image was also a test for a new telescope mount. After twenty months of frustration with my last mount, I decided to take advantage of a sale on the Sky-Watcher EQ6-R Pro and I’m glad I did! Right out of the box this mount performed wonderfully, guiding easily and consistently over the course of the entire night. While it isn’t perfect it is a great performer at it’s price point.

My first night on this image was the second with the mount. I spent the first few hours getting a good periodic error correction curve defined and testing it and various guiding options. About 2:30 AM I started to image this and I managed 270 20-second images with the luminance filter. Guiding was consistently around 0.6” RMS over the entire night.

The next night I managed to get red and blue filter data, again with good guiding performance. The following weekend we had an unheard of three clear nights in a row and I did green one night and more red, blue and luminance on the remaining nights. Overall it was 10.3 hours of good data. The mount performed wonderfully and the only thing slowing the process down was Sequence Generator Pro which seems to take a long time downloading images.

I preprocessed the data in PixInsight using darks, flats and flat darks. I also used local normalization at scale 256. Image integration used linear fit clipping and large and small scale pixel rejection.

One aspect of post-processing was going to be a challenge. Since the entire field was basically nebulous there were no obviously good points to use with DBE. I decided to use ABE and it definitely helped and didn’t appear to be leaching any nebula away.

Here was the entire process:

Luminance

  • Dynamic Crop
  • Automatic Background Extraction
  • Deconvolution
  • Multiscale Linear Transform (noise reduction)
  • Histogram Transformation
  • RBG Working Space

Individual R, G and B

  • Dynamic Crop
  • Automatic Background Extraction

Combined Image

  • Channel Combination of R, B and G
  • Photometric Color Calibration
  • Multiscale Linear Transform (luminance noise reduction)
  • Multiscale Linear Transform (chrominance noise reduction)
  • Histogram Transformation
  • RBG Working Space
  • LRBG Combination with luminance
  • TGV Denoise
  • Local Histogram Equalization
  • Multiscale Linear Transform (mild sharpening)
  • Curves Transformation (contrast and saturation)
  • Dark Structure Enhance
  • SCNR (to remove green from Sadr’s halo)
  • Multiscale Linear Transform (to shrink Sadr’s halo)

Aside form the challenge of gradient reduction mentioned earlier, the other challenge was reducing the halo around Sadr. Sadr is extremely bright compared to the other stars isn’t he frame and it’s halo was enormous. I used a combination of the GAME script (to generate a mask for the halo and MLT to remove four or five layers from the halo to dramatically shrink it making it less visually distracting. This left behind this browinsh looking nebula that I couldn’t find a way to handle. Normally that’s a sign of light pollution and in this case the light pollution was probably from the halo. I almost cropped Sadr and its halo out of the image but decided I liked it better as a wider image despite that flaw.

I did learn a few things for the future. I should raise the temperature on the camer from -20 to -15C. In the warm July nights the camera was struggling to get to that temperature. I think I’ve done everything I can do to speed up SGP and it still wastes a lot of time in between frames. I’m going to try an open source program called N.I.N.A. to see how it does. People are saying good things about it.

One night I was having trouble getting guiding to work in DEC. I went out and rebalanced the DEC axis and it worked fine. Definitely need to pay attention to that before leaving the system to run unattended.

I don’t think I’ve ever been completely satisfied by one of my efforts though I feel like I’m improving with each one. I learned a lot from this one and it was great to get five clear nights in less than two weeks. Who knows when the next time that will happen? I had to take advantage of it even though the moon was nearly full and I only had broadband filters. Despite all that I think this one of my best images so far. I’m hoping that new moon will be as kind to us as (nearly) full moon was.

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