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Contains:  NGC 7023
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The Iris and Ghost Nebula (NGC7023 and vdB 141), 


            Andrew Klinger
The Iris and Ghost Nebula (NGC7023 and vdB 141)

The Iris and Ghost Nebula (NGC7023 and vdB 141)

Technical card

Resolution: 3633x2719

Dates:July 12, 2018

ZWO B 1.25": 10x360" (gain: 76.00) -10C bin 1x1
ZWO G 1.25": 7x360" (gain: 76.00) -10C bin 1x1
ZWO L 1.25": 11x360" (gain: 76.00) -10C bin 1x1
ZWO R 1.25": 16x360" (gain: 76.00) -10C bin 1x1

Integration: 4.4 hours

Darks: ~64

Flats: ~30

Bias: ~200

Avg. Moon age: 28.80 days

Avg. Moon phase: 0.60%

Bortle Dark-Sky Scale: 1.00 job: 2153483

RA center: 316.810 degrees

DEC center: 68.468 degrees

Pixel scale: 2.530 arcsec/pixel

Orientation: 179.986 degrees

Field radius: 1.594 degrees

Locations: Chisos Basin, Big Bend National Park, TX, United States

Data source: Traveller


I captured this dusty duo from my stay in Big Bend National Park, TX, a Bortle 1 on the dark sky rating. To take advantage of the dark skies, I chose a target that is all reflection nebula and non-reflective molecular clouds. Cepheus is full of this dust that can only be revealed from dark skies!
With only 4hrs of integration time, I would normally be hesitant to call it “done”, but the dark skies really helped bring the signal through, and some generous noise reduction helped as well. When I return to true dark skies in the future, I’ll most likely continue adding data to this, as it can only get better!

OTA: William Optics GT81 w/0.8x reducer (382mm fl at f/4.7)
Mount: Orion Sirius EQ-G (HEQ-5)
Guidescope: Orion 50mm guidescope
Guiding camera: Orion StarShoot Autoguider
Imaging camera: ZWO ASI1600MM-Cool


Location: Chisos Basin, Big Bend National Park, TX (Bortle 1)
Dates: 7/11/18, 7/12/18
Gain: 76 Offset: 15
Camera temp: -10C
L: 11x360"
R: 16x360"
G: 7x360"
B: 10x360"
Total integration time: 4hr 24min
64x darks per calibration
30x flats per calibration
200x bias (master bias in library)

Batch PreProcessing script to generate calibrated images
DynamicCrop each master
DBE on each master
LinearFit R and B to G

RGB processing:
SCNR green 50%
TGV and MMT noise reduction (via Jon Rista's method)
HistogramTransformation x3
SCNR green 100%
CurvesTransformation for saturation
ColorSaturation to further saturate blues and orange dust
CurvesTransformation slight contrast

L processing:
TGV and MMT noise reduction (via Jon Rista's method)
HistogramTransformation x2 to stretch image
Duplicated the image to create a starless version, using a starmask and several iterations of MMT and MT. Then pushed the faint nebulosity in the starless version using PixelMath expression: "1-(1-$T)*(1-$T)"
Combined the starless version with the image using PixelMath expression "F=0.4; (1-(1-$T)*(1-s)*F)+($T*~F)" followed by the same expression with F=0.2 (s=starless photo).
HistogramTransformation to move blacks in
ExponentialTransformation with a mask showing just the dust to bring it forward a tad more

Combined L and RGB with LRGBCombination tool
CurvesTransformation to neutralize background color
MorphologicalTransformation for slight star reduction
ACDNR final noise reduction
Resampled to 80% for web posting



Andrew Klinger
License: None (All rights reserved)

Sky plot

Sky plot


The Iris and Ghost Nebula (NGC7023 and vdB 141), 


            Andrew Klinger