The Spider Nebula in Auriga

Tricolor narrowband image with RGB stars.


Exposure: Total exposure time 30 hours, 25:30:26 x 20 mins SII:Ha:OIII and 30:26:30 x 2 mins R:G:B. All bin 1x1. Captured between November 2017 and January 2018.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
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
Channel Combination to merge RGB images
Dynamic Crop

3. Narrowband Linear Processing
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask (on Ha only)

4. Narrowband Stretching
Histo Trans
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 luminance mask to protect highlights

5. RGB Linear Processing
Dynamic Crop
Dynamic Background Extraction
Photometric Color Calibration

6. RGB Stretching
Histo Trans
Curves Trans to increase saturation

7. Color merge
Merged narrowband channels in PixelMath, mapping SII:Ha:OIII to R:G:B
SCNR to shift green to yellow
Remove magenta halos and casts in corners:
Invert image
SCNR on green
Re-invert image
Curves to increase saturation
Very mild Local Histogram Equalization

8. Star removal/reduction
Stars were reduced and then replaced with RGB stars, following David Ault’s technique

9. Final
Reduction of reflection/halo around brightest star following David Ault’s technique
Photoshop:
Desaturate blue halos around bright stars
Clone stamp and blurring to finish reflection/halo reduction
Downsize 50% and save as JPG