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The Veil Nebula - Five panel mosaic


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Hi everyone.

Here's my first attempt at a mosaic of the Veil Nebula. This image includes the Eastern Veil (left) and the Western Veil (right), which also include many other structures which have their own designations! I'd recommend checking out this annotated image from Wiki which points out the main structures: https://en.wikipedia.org/wiki/Veil_Nebula#/media/File:Cygnus_Loop_Labeled.png

Initially I didn't intend on making a mosaic, but my original field of view was at the centre which resulted in the veil being right at the edges of the frame. I figured I would have a crack at creating a mosaic by expanding my field of view by image each of the four corners and ensuring a good enough overlap between panels. Full equipment, acquisition and processing details are included below the image.

Any questions, comments, feedback, tips or tricks are welcome!




  • Camera: ASI533MC-Pro
  • Telescope: RedCat51
  • Mount: EQ6-R
  • Guide Scope/Camera: WO 32mm/ASI120MM Mini
  • Filter: Optolong l-eXtreme
  • Peripherals: ASI Air Pro, TP-link WiFi extender, Dew Heaters


  • Gain: 100 (unity)
  • Sensor temp: -10°C
  • Subs: 180s | Panel 1 = 30 subs | Panel 2 = 25 subs | Panel 3 = 30 subs | Panel 4 = 29 subs | Panel 5 = 81 subs | [Total integration time = 9.75hrs]
  • Darks: 50
  • Flats: 30
  • Dark Flats: 50
  • Dates: 23rd Sep 2021 | 11th Oct 2021 | 12th Oct 2021 | 23rd Oct 2021 | 01st Nov 2021 | 02nd Nov 2021
  • Area: Northern Hemisphere, Bortle 5 zone



  • WBPP script
    • Chuck subs and calibration images from all nights into script
    • Calibrate by date of imaging; do not register or create master lights
  • Manually perform SubframeSelector on debayered subs, apply weights per Adam Block script (https://youtu.be/g6SUBB8uu4E) and reject subs which have poor FWHM, star quantity and eccentricity (perform this for each panel)
  • Register subs and create master light for each panel
  • Save each panel as separate XISF files

Processing (per panel)

  • Crop out any overlapping from registration
  • Dynamic Background Extraction to remove any gradients
  • Colour calibration
  • Plate solve each panel [Script > Image Analysis > ImageSolver]
  • Align each panel based on RA and DEC co-ordinates [Script > Utilities > MosaicByCoordinates]
  • Merge all panels and create master mosaic image [Process > GradientDomain > GradientMergeMosaic]
  • Save mosaic as XISF

Process (master mosaic)

  • Background neutralisation and re-run colour calibration to ensure colours match across all panels
  • Histogram transformation
  • StarNet to remove stars and create two separate images: Stars and Starless
  • Starless
    • EZ Denoise
    • Create mask and invert to protect background
    • SCNR (green, amount = 0.35, to keep teal colour)
    • Curves transformation to boost colours and saturation slightly
    • HDR Transformation to reduce bright regions
    • Remove mask
  • PixelMath to add stars back in
  • EZ Star Reduction > Adam Block method
  • Histogram transformation to shift black point towards left side of histogram without clipping
  • Unsharp mask
  • Add 20px black border
  • Save as JPEG, 100% quality

*** END ***


When I first tried the mosaic I had hardly any data and didn't get a nice blend between panels. I had about 4hrs of time on the centre panel, but just ~30 minutes on three of the corners, and 0 minutes on the lower right, see Fig.1. I was trying out the mosaic tools to see how it would all work. At this point, all I had done was crop each panel to the same dimension and performed a stretch: I didn't perform any background extraction or I tried both the "average" and "overlay" functions of the "GradientMergeMosaic" process with mixed results. The average method seemed to produce the best join between panels whilst the overlay method seemed to maximum the extra signal from the centre panel at the expense of a poorer, more obvious join in the corner panels. The script seemed to struggle with the larger stars at these boundaries.

By the time I gained enough subs (~30 x 3 min subs = 90 mins) per panel, the merge seemed to perform much better even though the centre panel was around 4 hrs. My planning paid off too, as I had very little "black" regions where the panels didn't line up around the edges, so I didn't need to perform too aggressive of a crop. Fig.2 shows the overlap between the five panels, with the white regions showing the most amount of overlap and signal (see if you can spot the boundaries!).







Edited by Richard_
Delete rogue spaces!
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