Sharpless 2-112 in Cygnus
Sh2-112 is a emission nebula near Deneb. The exciting star for this nebula is the O8V class star BD+45 3216 (SAO 49801). The nebula appears to be about 5700 light years away.
Exposure: Total exposure time 15 hours, 13:15:27 SII:Ha:OIII. All bin 1x1. Captured over 8 nights between June and September 2018.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: FWHM of subs about 2 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arcsecs/pixel (50% reduction)
Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.1 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.17140 (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon 5nm Ha/SII, 3nm OIII, Type IIe LRGB
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB_nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.0.0.8
Guide SW: PHD2.6.3, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: PlateSolve 2, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2
Processing Workflow by Workspace in PixInsight 1.85
1. Calibration
BatchPreProcessing with flats, darks and bias, using Cosmetic Correction with master dark
2. Stack and Mure Denoise
Blink to preview and reject a few frames
Subframe Selector to confirm selections
Image Integration
Mure Denoise
3. Linear Processing
Dynamic Crop
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask (on Ha only)
4. Stretching
Histo Trans
Masked Stretch
Curves Trans
Noise Reduction following David Ault’s Astro Imaging Channel tutorial:
TGV Denoise
Aggressive Multiscale Median Transform to remove lumpiness in background, using an inverted and blurred range mask to protect highlights
Local Histogram Equalization
5. Color merge
Merged narrowband channels in PixelMath, mapping SII:Ha:OIII to R:G:B
SCNR to shift green to yellow
6. Star removal/reduction
Stars were reduced and then replaced with a less stretched version, following David Ault’s technique
7. Final
Remove magenta halos and casts in corners:
Invert image
SCNR on green
Re-invert image
Mild Curves Transformation
Downsize 50% and save as JPG
