NGC6992 - Eastern Veil Nebula in HOO - Leaping from the Waves

Original Post - 01-08-2023:

There have been over a month of cloudy nights, so I decided to work on a first version of this target. It is short set of Ha and OIII data from one night that turned out nicely. I had planned to delay until I had some RGB subs for a separate star layer, but the HOO blend worked pretty well for this version. No idea if it mattered, but I still set the SPCC filter to use the SII wavelength even though OIII mapped there. I skipped Interactive Normalization and let the WBPP batch script do the initial integration. This meant there were no sub ref frames to do for the Subframe Selector process. I only used it to ditch lessor subs after the WBPP script.

Target Workflow (H,O subs):

ASIFitsView (Blink Equivalent)
- Review all subs and remove visually bad frames (none this time)

WBPP
- Cosmetic Correction Applied
- Pedestal added to avoid clipping in later processes = 800DN
- Set Local Normalization (Automatic)
- Check Image Integration
- Do not do Drizzle Integration as subs still to be weeded out in next step

Subframe Selector
- Sort by PSF Signal Weight and Star Count to weed out subs that stray far below median values

Drizzle Integration
- Use Normalization Files

Dynamic Crop
- Barely trim edges

Linear Fit
- use Statistics to find the lowest channel Median value for reference sub = H

LRGB Combination
- Uncheck L channel and load H to R, O to G, O to B
- Uncheck Chrominance Noise Reduction

DBE
- Apply Subtraction with Tolerance 2.0, Smoothing Factor = 0.65

BlurXTerminator
- Run PSFImage script and get average of the FWHMx and FWHMy values = 3.22
- Turn off Auto PSF and set to 3.22
- Sharpen Nonstellar = 0.7

Image Solver Script
- Search and set target from database = NGC6992

Spectrophotometric Color Calibration
- White Ref = Photon Flux
- QE Curve = Ideal QE Curve
- Check Narrowband filters mode
- Set Wavelengths (ZWO 7nm - H=656, O=500, S=672)
- Make very small background preview
- Set Background Neutralization->Region of Interest->From Preview->Select the background preview

Bill Blanshan SCNR
- Amount = 0.45

NoiseXTerminator
- Turn on 24-bit STF lookup tables
- Apply with Defaults

StarXTerminator
- Check 'Generate Star Image' and 'Unscreen Stars' for HOO
- Remove stars from HOO image and save as HOO_Starless and HOO_Stars

Generalized Hyperbolic Stretch on HOO_Starless and HOO_Stars
- Multiple iterations to zero in and finalize with Linear at end

Extract CIE Luminance from HOO_Starless
- for use in later steps
- save as HOO_Starless_L

Histogram Transformation on HOO_Starless_L
- Darken Background without clipping

Curves Transformation
- Apply HOO_Starless_L as mask to HOO_Starless
- Adjust contrast and colors to taste
- Use Bill Blanshan blue color mask to enhance nebula

Local Histogram Equalization
- Apply HOO_Starless_L as mask
- Large structures - KR = 150, CL = 1.3, Amount = 1.0, 10-bit
- Small structures - KR = 50, CL = 1.3, Amount = 1.0, 8-bit

Pixel Math to Mask Stars from Main Nebula Signal
- Formula = HOO_Stars - HOO_Starless_L
- Save as HOO_Stars_masked

Pixel Math to Re-add Stars
- Formula = ~((~HOO_Starless)*(~HOO_Stars_masked))

Image->Geometry->Rotate 180 degrees
- Save final and JPG for upload

Sessions

Total Integration Time:

July 31, 0022 - 23 * 300.0 seconds
ZWO H-alpha 7nm 1.25"
July 31, 0022 - 20 * 300.0 seconds
ZWO O-III 7nm 1.25"

Catalogues

Caldwell New General Catalogue

Targets

C33 NGC6992 NGC6974 NGC6979 NGC6995

Gear

Telescope: William Optics Gran Turismo 81 IV
Camera: ZWO ASI1600MM Pro
Mount: Sky-Watcher EQ6R-Pro