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Getting plate-solving status, please wait...
The Seagull Nebula in Ha-OIII, 


            Jim Lindelien
Powered byPixInsight

The Seagull Nebula in Ha-OIII

Getting plate-solving status, please wait...
The Seagull Nebula in Ha-OIII, 


            Jim Lindelien
Powered byPixInsight

The Seagull Nebula in Ha-OIII

Imaging telescopes or lenses: William Optics Star71-II

Imaging cameras: ZWO ASI128MC Pro

Mounts: iOptron CEM120EC

Guiding telescopes or lenses: ZWO 30mm f/4 Mini Guide Scope

Guiding cameras: ZWO ASI290MM mini

Software: ASCOM Platform 6  ·  NINA  ·  darkarchon EZ Processing Suite  ·  Pleiades Astrophoto PixInisight 1.8 Ripley (x64)  ·  Windows 10 Remote Desktop  ·  Cartes du Ciel  ·  Open PHD Guiding PHD2 Guiding  ·  StarNet++  ·  Affinity Photo

Filters: STC Duo-Narrowband 50mm Square

Accessory: Baader UFC Filter Slider  ·  QHYCCD Polemaster  ·  ZWO EAF Focuser  ·  Guzila Fanless Mini PC Intel Core i5-5257U  ·  iOptron Tri-Pier 360

Dates:Feb. 10, 2021

Frames:STC Duo-Narrowband 50mm Square: 33x300" (2h 45') (gain: 240.00) -10C bin 1x1

Integration: 2h 45'

Darks: ~32

Flats: ~64

Flat darks: ~64

Avg. Moon age: 28.23 days

Avg. Moon phase: 1.89%

Bortle Dark-Sky Scale: 4.00

Mean FWHM: 3.30

Temperature: -8.00

Astrometry.net job: 4361979

RA center: 7h 9' 36"

DEC center: -10° 45' 40"

Pixel scale: 3.561 arcsec/pixel

Orientation: -36.260 degrees

Field radius: 3.532 degrees

Resolution: 5950x3950

Locations: N. America, Pahrump, Nevada, United States

Data source: Backyard


The Seagull Nebula in bi-color Ha-OIII (HOO).

A comment about workflow for the technically curious:

Rather than treating the OSC data as a color image to be de-Bayered with the VNG algorithm--which would have caused Ha and OIII signal crosstalk too early in the processing workflow--I instead conceptualized the Bayer sensor as four interleaved but independent mono cameras and used PixInsight's SplitCFA process to make cleaner separations of the Ha signal contained in the red CFA pixels, and a 3x deeper stack (for better SNR) of the dimmer OIII data by summing together the two green plus the blue CFA pixels. Thus, this is a kind of hybrid binning.

Atmospheric turbulence convolves photons across neighboring pixels regardless. Dithering the sub exposures plus 2x drizzle integration of the stacks restored much of the original sensor resolution to these channels despite their interleaved nature in this hybrid binning strategy. Given all the above, with regard to the signals' spatial frequencies along the X and Y axes, the Nyquest Sampling Theorem is respected and so an acceptable image can result.

Versus a monochrome camera, of course, per unit time less silicon is exposed to each signal channel and there is inefficient double filtering of the photons through the sandwich of NB and RGB filters, which degrades SNR, but this object is bright, and not much imaging time is needed to overcome such inefficiencies.

Thereafter the HOO post processing proceeds just as it does if Ha and OIII were imaged separately on a normal monochrome sensor camera.


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  • Final
    The Seagull Nebula in Ha-OIII, 


            Jim Lindelien
  • The Seagull Nebula in Ha-OIII, 


            Jim Lindelien


Description: Portrait version--after you open the square thumbnail--and intentionally mirrored. I've left the other version as Final for PC viewing but this one's my personal preference as it strikes me as the more dramatic presentation even though the data are identical.

Uploaded: ...

Sky plot

Sky plot


The Seagull Nebula in Ha-OIII, 


            Jim Lindelien