Sh2-134 and Sh2-135 — Wide Field
October 9, 2017
This wide field Lies in Cepheus, approximately midway between the Bubble Nebula and IC1396. I made an annotated version to identify some of the other interesting objects in this image, such as dark nebulae B73 and B74 and open cluster NGC 7261. The estimated distance to Sh2-135, which lies near the centre of this image, is 6,200 light years. There is a striking similarity between the structure to the lower left of centre and the Propeller Nebula, which lies not far away.
Moravian G3-16200 EC camera (on loan from O’Telescope), Optolong Ha, R, G and B filters, Takahashi FSQ-106 ED IV at f/3.6, Paramount MX, unguided. Acquisition with the SkyX, focused with FocusMax, scripted with CCD Commander. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Moderate moonlight for Ha, no moonlight for RGB, average transparency and seeing.
31x5m R, 34x5m G, 33x5m B and 124x10m Ha unbinned frames (total=28hr50m).
Creation and cleanup: The BatchPreProcessing script was used to perform calibration, cosmetic correction and registration of all frames. LocalNormalization, ImageIntegration and DrizzleIntegration were used to make the Ha, R, G and B masters. The masters were cropped to remove edge artifacts. R, G and B were combined to make an RGB image which was processed with DBE, BackgroundNeutralization and ColorCalibration.
Combining Ha and RGB data: The NBRGBCombination script was run with default settings using Ha for red narrowband. PhotometricColorCalibration was applied.
Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the NB-RGB image. Layer settings for threshold and strength: Layer 1: 3.0 0.8 Layer 2: 2.5, 0.7 Layer 3: 2., 0.6 Layer 4: 1.0, 0.2 Layer 5: 0.5, 0.1.
Stretching: HistogramTransformation was applied to the NB-RGB image to make a pleasing, bright image.
Creation and cleanup of SynthL: The four channel masters were processed with DBE and then integrated (average, noise weighted, no rejection) using ImageIntegration to create the SynthL.
Deconvolution: A star mask was made to use as a local deringing support image. A copy of the image was stretched to use as a range mask. Deconvolution was applied (50 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 30 stars).
Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the background areas of the NB-RGB file. Layer settings for threshold and strength: Layer 1: 3.0 0.8 Layer 2: 2.5, 0.6 Layer 3: 2., 0.5 Layer 4: 1.0, 0.2.
Stretching: HistogramTransformation was applied to the SynthL to make a pleasing, bright image.
Noise Reduction and Re-Stretch: TGVDenoise was applied in Lab mode with 300 iterations with a range mask applied to protect high signal areas. This was followed by a HistogramTransformation to raise the black point (but with no clipping).
Local Contrast Adjustment: Bright areas of the nebula were processed with two passes of LocalHistrogramEqualization with max contrast of 1.5 (scale 50, strength 0.45 and scale 150, strength 0.18) using a mask to protect background and stars.
Combining SynthL with NB-RGB:
The StarReduction script was used to reduce the size of stars in the NB-RGB image to match the SynthL. The processed SynthL was applied to the NB-RGB image using LRGBCombine with Chrominance noise reduction on and all settings at default.
Final Steps: MultiscaleLinearTransform was used to sharpen the structures in the bright parts of the nebulae (layers 2-4 at 0.1), using a mask to protect background and stars. The DarkStructureEnhance script (strength 0.1) was used to increase contrast between dark nebula and brighter regions. Background, nebula and star brightness, contrast and saturation were adjusted in several iterations using Curves with masks as required. A range mask was used to protect background and stars while adjusting the hue of the nebula to reduce a slight orange cast. The image was reduced in size by a factor of 2 with IntegerResample to restore resolution to its original value.
Image scale is about 3.2 arcsec per pixel for this camera/telescope combination.