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Caldwell 4

The Iris Nebula

Caldwell 4

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The Iris Nebula (also known as NGC 7023 and Caldwell 4) is a bright reflection nebula in the constellation Cepheus. Wikipedia

Description

Acquisition Details

Dates August 28th, 2022 (Waxing Crescent Moon)
Frames 30x300” (5mins), 2h 30m of total integration time
Focal Length 360mm (f/6)
Camera ZWO ASI533MC-Pro (gain 100, cooled at -5°C)
Telescope TS-Optics Photoline 60mm Doublet Apochromatic Refractor
Accessories 1.0x Flattener
Filters TS-Optics 2” UV & IR Cut Filter
Mount Sky-Watcher EQ6R-Pro
Guide Scope Angeleyes Mini Guidescope 30mm f/4
Guide Camera ZWO ASI 120MM mini
Computer ZWO ASIAIR Pro

Processing Details

I stacked the ligths frames in Siril using the OSC Preprocessing Without DBF (Darks, Biases, Flats) script. I decided not to use any Dark, Bias or Flat frames. I might try to create a dark frame library later, but the ASI533MC-Pro is considered a camera that can do without darks given the absence of amp glow.

I then used the following tools:

  • Photometric Color Calibration
  • Asinh Transformation (stretch 600.0, black point 0.001)
  • Histogram Transformation (mid 0.077, low 0.093, high 1.000)
  • SCNR (type 0, amount 1.00, preserve true)
  • Saturation enhancement (amount 0.35)
  • Background extraction (Correction: Subtraction)