Narrowband NGC 7822 – Modified SHO

NGC 7822

Acquired 2017-09-26 - 2017-10-14 from TriStar Observatory TinyObs

28 x 900" Hα, 27 x 900" NII, 70 x 900" OIII, 40 x 900" SII : 41h 15m Total Integration

Stellarvue SV80ST

Astro-Physics Mach-1 GTO

Atik 414EX

Astrodon 1.25" 3nm Ha, NII, OIII, SII filters

QHY5-L II Guidecam

Sequence Generator Pro


Figured I’d try to throw in some NII for a change since…well…I have the filter, why not use it? Overall, not really worth the effort imo. It does show some VERY minor differences from the Hα signal in darker areas, but not enough to justify the several extra hours of imaging time.

Feel like I’m getting a better handle on taking narrowband images where I envision them when I first see the data. Color management is still a huge issue for me, and likely always will be, but I’m getting a better feel for “what makes a thing look like i think it looks”, so that’s a start anyway.

Not at all confident about the lower corners of this one. Very difficult for me to tell what’s nebula, what’s LP/noise gradient, and what’s just my imagination. The reddish corners are a “best compromise” result between “wow, the rest of the image looks nice but the corners are horrendous” and “might as well be monochrome”.

This is probably the last image for a bit. The Mach 1 has picked up a rather horrendous (and well out of spec) bit of PE and aberrant behaviour in the RA axis, and is currently sitting at AP’s shop for some troubleshooting and attention. When it returns, I may or may not throw it back in TinyObs, depending upon the completion level of Obs 2.0

Acquisition Details

  • Date and conditions
    • Acquired 2017-09-26 – 2017-10-14 from TriStar Observatory TinyObs
    • Bortle class 6-7
    • 28 x 900″ Hα, 27 x 900″ NII, 70 x 900″ OIII, 40 x 900″ SII : 41h 15m Total Integration
    • Equipment
      • Stellarvue SV80ST
      • Astro-Physics Mach-1 GTO
      • Atik 414EX
      • Astrodon 1.25″ 3nm Ha, NII, OIII, SII filters
      • QHY5-L II Guidecam
    • Software
      • Sequence Generator Pro
      • PHD2

Processing Details

  • All processing in PixInsight
    • Calibration of all light frames w/ 50-frame Dark masters, 200 frame Bias master, 50 frame Flat masters per filter
    • SubframeSelector to weight frames, (100 * SNRWeight)/(FWHM+Eccentricity). Frames w/ high eccentricity or FWHM rejected.
    • StarAlignment to register all frames
    • LocalNormalization applied using highest weighted frame from each set as reference
    • DrizzleIntegration x 2 of each filter set
    • RGB Processing
      • Masters cropped equally
      • DynamicBackgroundExtraction applied to each master, subtraction mode
      • Synthetic Luminence created using PixelMath
        • .8 * Ha + OIII + SII (Rescaling on)
      • MMT Noise Reduction applied to all masters
      • Masters stretched using HistogramTransformation to equal black points.
      • RGB Combination using PixelMath
        • .5 * Ha + .5 * NII to create HaNII
        • SII:HaNII:OIII
      • SCNR to Remove Green, amount .8
      • PixelMath for Magenta Removal
        R : $T[0]
        G : iif(min($T[0],$T[2])>$T[1],min($T[0],$T[2]),$T[1])
        B : $T[2]
      • MorphologicalTransformation through star mask to reduce stars in color master, using X/+ method
    • Lum Processing
      • Deconvolution through brightness mask w/ stars removed, using DynamicPSF & StarMask local support, 30 iterations
      • UnsharpMask through same brightness mask, Sigma 2.0, amount .8
      • MMT for very light NR through inverted brightness mask, heavily stretched.
      • MorphologicalTransformation through star mask to shrink stars, using round pattern, amount .15
      • DarkStructureEnhance script, about .4
      • HistogramTransformation to stretch SynthLum
    • Final Processing
      • LRGBCombination to combine SynthLum w/ RGB
      • CurvesTransformation to boost saturation, adjust colors via Hue.
      • Final light SCNR, amount .2







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