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Jellyfish Nebula, SHO

The cosmic sea jellyfish in Sulfur ΙΙ, Oxygen ΙΙΙ and Hydrogen-α (SHO). The remnant of a dead star, a supernova that lit up the heavens 30,000 years ago.

Processing Details

PixInsight

Star alligment of the linear Ha, OIII and SII data using StarAllignment (Hydrogen-α frame as a reference).

Dynamic Crop on all frames using the same process.

Background Noise Resduction with Dynamic Background Extraction (using 50 points on non-nebula areas, separately for each frame).

The auto-stretch of the OIII frame (weaker emmision of all three) that performed with STF (ScreenTransferFunction) with unlinked RGB channels, was applied on both the Hydrogen-α and OIII frames using HistogramTransformation to balance the emissions.

Noise reduction was performed with MultiscaleLinearTransform to reduce the noise and prepare them for the Pixel Math process. 4 layers with the following settings (R as default):

  • Layer 1: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 2: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 3: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 4: Threshold 0.500, Amount 0.50, Iterations: 1

The Pixel Math formula that was applied:

  • R: (0.76 * SII) + (0.24 * HA)

  • G: (0.85 * HA) + (0.3 * OIII) + (0.15 * SII)

  • B: OIII

The green was reduced with SCNR at 9.0, the red at 0.23 and green again at 0.23.

Further noise reduction was applied with ACDNR and StdDev of 1.0 and Amount 0.50.

Star Reduction was applied with StarMask at 0.04000 Noise threshold, Scale 6 and Structure Growth as 0, 1 and 2 (Large-scale, Small-scale and Compensation).

Curves Transformations were applied to boost RGB/K and Saturation.

Jellyfish Nebula Sho 0219 CurvesTransformations

Photoshop

Selective Sharpening with High Pass Filter (radius 1.6).

Tech Card

Date / Location

26th & 27th February, 25th, 28th March 2019, Bedworth, GMT+0, United Kingdom, Bortle Class 5 ~SGM: 19.57 mag./arc sec2

Equipment

Camera: ZWO ASI 1600MM-PRO USB 3.0 Mono (Type CMOS)

Sensor Cooling Temperature: -15C

Filters: 1.25" 5nm Astrodon Ha, 1.25" 3nm Astrodon OIII, 1.25" 3nm Astrodon SII

Imaging Telescope: Takahashi FS-60CB

Correcting Lens: Takahashi Reducer 0.72x (composite focal length at 264mm and focal ratio at f/4.9)

Mount: iOptron CEM25EC

Image Quality

12Bit ADC (FITS)

Exposure time per image / number of composities and sensitivity

50 x 180" Ha subs (Unity Gain, Gain: 139, Offset: 21, Binning 1x1)

42 x 180" OIII subs (Unity Gain, Gain: 139, Offset: 21, Binning 1x1)

42 x 180" SII subs (Unity Gain, Gain: 139, Offset: 21, Binning 1x1)

Total Integration Time

6hrs 42mins

Calibration Frames

20 Darks, 20 Flats

Software

PixInsight 1.8 Core

Photoshop

SharpCap