This is one of my longer projects, with 84 hours of long exposure time over 2 seasons going into this photo. Sh2-224 is an extremely faint nebula, and this is what a single 10 minute long exposure (through a Ha narrowband filter) of it looks like. I ended up getting ~83 hours of narrowband exposures like this, plus about an hour of RGB images for the stars. Because it's so faint, if the moon was up at all I did not shoot it, which cut the number of clear nights I could reasonably image it in half. The nebula itself is false color (although the HOO palette I used is fairly close to natural color), the stars were taken with RGB filters and are true color. With this project I finally managed to learn how to do some starless processing techniques for combining the stars+nebula

Captured over 27 nights between February 2021 and April 2022, from my Bortle 6 driveway

Places where I host my other images:

Instagram | Flickr

Equipment:

• TPO 6" F/4 Imaging Newtonian

• Orion Sirius EQ-G

• ZWO ASI1600MM-Pro

• Skywatcher Quattro Coma Corrector

• ZWO EFW 8x1.25"/31mm

• Astronomik LRGB+CLS Filters- 31mm

• Astrodon 31mm Ha 5nm, Oiii 3nm, Sii 5nm

• Agena 50mm Deluxe Straight-Through Guide Scope

• ZWO ASI-120mc for guiding

• Moonlite Autofocuser

Acquisition: 83 hours 52 minutes (Camera at Unity Gain, -20°C)

• Ha - 266x600"

• Oiii - 231x600"

• Red- 14x90"

• Green- 14x90"

• Blue- 14x90"

• Darks- 30

• Flats- 30 per filter

Capture Software:

• Captured using N.I.N.A. and PHD2 for guiding and dithering.

PixInsight Processing:

• BatchPreProcessing

• SubframeSelector

• StarAlignment

• Blink

• ImageIntegration

• DrizzleIntegration (2x, Var β=1.5)

Narrowband processing:

• DynamicCrop

• DynamicBackgroundExtractions

• NoiseXTerminator

• StarXterminator to completely remove stars for starless processing

to be later replaced by RGB stars. doing this allows the nebula to be stretched without worrying about blowing out stars

• HistogramTransformations to stretch nonlinear

RGB Linear Processing:

• DynamicCrop

• DynamicBackgroundExtractions

• ChannelCombination to combine monochrome R, G, and B frames into color image

• PhotometricColorCalibration

• Slight SCNR Green

• HSV Repair

super useful for putting color back into blown out star cores

• StarXterminator to generate stars only image

basically just getting rid of the background

• ArcsinhStretch + Histogram transformation to stretch nonlinear

Combining Channels:

• ChannelCombination to combine stretched Ha and Oiii images into color image

Ha mapped to red channel, Oiii to Green and Blue

• HistogramTransformation to re-linearize HOO and RGB stars images

• PixelMath to add RGB stars only image to starless HOO image

HOO + Stars the math was simple

• HistogramTransformation to bring HOO+Stars pic back to nonlinear state

Nonlinear:

• Shitloads of CurveTransformations to adjust lightness, saturation, contrast, hues, etc. with various masks

• ColorSaturation to selective saturate/desaturate specific hues

• More curves

• Slight SCNR Green

• NoiseXterminator

• LRGBCombination with extracted L as luminance, used for chrominance noise reduction

• even more curves

• color saturation again

• SCNR to remove some green star color

• EZ star reduction

• NoiseGenerator to add noise into reduced star areas

• LocalHistogramEqualization

• guess what baby more curves!

• Extract L --> LRGBCombination again with mask for larger scale background chrominance noise reduction

• Resample to 70%

• Annotation

that 10-minute exposure image sure puts the work into perspective, if your amazing write-up wasn't clue enough already

Amazing!