Globular Cluster Messier 71 in Sagitta
Exposure: Total exposure time about 2.6 hours, 19 x 2 mins per LRGB channel. All bin 1x1. Captured June 20, 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 imaging at f5.7
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 IIi LRGB
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB_nStep with driver version 6.0.7
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.0.0.4 beta
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 and bias, using Cosmetic Correction with master dark
2. Stack and Mure Denoise
Blink to preview frames
Subframe Selector to weight by FWHM
Image Integration
Channel Combination to merge RGB channels
Dynamic Crop
3. Luminance Linear Processing
Automatic Background Extraction. Executed first for subtraction, then for division.
Dynamic Background Extraction
Deconvolution, using Dynamic PSF, multiple iterations of Star Mask to create a deringing support image, and using a stretched luminance as a mask.
4. Luminance Stretching
Histogram Trans
Curves Trans
Noise Reduction with TGV Denoise and Multiscale Median (following David Ault’s Astro Imaging Channel tutorial).
5. RGB Linear Processing
Automatic Background Extraction
Dynamic Background Extraction
Deconvolution on blue channel to bring FWHM close to green channel
Photometric Color Calibration
6. RGB Stretching
Histo Trans and Curves Trans
TGV Denoise
7. Color Combine
LRGB merge
8. Background Removal
In Photoshop, desaturate comatic blue halos
Create background image and export it back to PI
PixelMath to subtract background from image
9. Final
Save as TIFF
Downsize 50% and save as JPG
