Sh2-140
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January 15, 2025
Sh2-140 is a fairly large emission nebula in Cepheus. I thought this would be an excellent target for the Sky-Watcher Esprit 120 that I have been using.
This emission nebula lies about 3000 light years from Earth. The glowing gas is mostly hydrogen, which emits mainly red and some blue light. The brightest areas also contain oxygen, which emits at green and blue wavelengths. It is part of the Cepheus Bubble, and is considered to be a stellar nursary. Near the top centre of the image is reflection nebula GN 22.12.3. I couldn’t find any information about it other than its catalogue number (with the Seti Astro What’s In My Image script).
This turned out to be my final image capture for 2025 (though I still have several data sets to process). The weather has been poor for imaging for the last two and a half months.
Tekkies:
Acquisition, focusing, and control of Sky-Watcher Wave 150i mount and other equipment with N.I.N.A. and Green Swamp Server. Primalucelab 3″ ESATTO focuser, ARCO rotator, GIOTTO flat panel and ALTO cover motor. Equipment control with Primalucelab EAGLE 6 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Acquired under average transparency and seeing and variable moonlight between October 27 – November 2, 2025.
Sky-Watcher Esprit 120, QHY168C camera, Optolong L-Quad Enhance filter.
68 x 5m = 5hr 40m
Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, debayering, weighting, registration, integration and Drizzle integration of all frames (1x drizzle, 1.0 Drop Shrink, Circular kernel).
Gradient Removal: Dynamic Background Extraction was applied.
Colour Calibration: BlurXterminator was applied to the RGB master with Correct Only selected, followed by SpectrophotometricColorCalibration. The darkest patch in the image was selected for the background reference.
Deconvolution: BlurXterminator was applied to the RGB master with Automatic psf , star sharpening set to 0.5, and non-stellar sharpening set to 0.9.
Linear Noise Reduction: NoiseXterminator was applied with settings Amount=0.9 and Iterations=4.
Stretching: MultiscaleAdaptiveStretch was applied to make a pleasing image with the darkest pixels in the image at approximately 0.11.
Nonlinear Processing
Star Removal: StarXterminator was used to remove the stars from the master, with default settings. The stars-only image was retained.
Nonlinear Noise Reduction: NoiseXterminator was applied with Amount=0.9 and Iterations = 4
Re-stretch: HistogramTransformation was used to boost contrast by moving the dark point to the toe of the histogram and slightly decreasing the mid-point slider.
Contrast Enhancement: LocalHistogramEqualization was applied three times. A Contrast Limit of 1.5 and 1 iteration was used for each LHE application (scale 300, strength 0.2; scale 150, strength 0.25, scale 40, strength 0.25).
Sharpening: MultiscaleMedianTransform was applied. (Layers 2 – 4 with strengths of 0.03 0.04, and 0.02 respectively).
Contrast, Brightness and Colour: Brightness, contrast, hue, and saturation were adjusted in several iterations using CurvesTransformation, ExponentialTransformation and the Jurgen Terpe Selective Color Correction script, with masks as required.
Stars-only steps: The CIE L* channel (i.e. the lightness channel) was extracted from the stars-only image and then applied to the star image as a mask. CurvesTransformation’s Saturation slider was used to boost colour in the stars.
Star Restoration: The PixelMath expression combine(starless, stars, op_screen()) was used to combine the starless starless image with the stars-only image. The StarReduction script was applied with small star protection enabled (Tranfer method, strength 0.4) to slightly reduce the larger stars.
Final Steps: Background, nebula, and star brightness, contrast, and saturation were adjusted in several iterations using CurvesTransformation with masks as required. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving as a jpg. The finder chart was made using the FindingChart process.
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