M76 - The Little Dumbbell Nebula

The Little Dumbbell Nebula gets its name because it kinda looks like a tinier version of the Dumbbell Nebla M27 (yes, a different palette was used for this pic). It's really tiny compared to the uncropped FOV. I'm a lot happier with this attempt at it, compared to my 2019 pic of M76 with the same equipment. I know It's a bit out of season rn but I needed something to shoot at the start of the night. The nebulosity itself is false color, but the stars are true color RGB. Captured over 10 nights in Feb/Mar 2024 from a bortle 9 zone (I could only get a couple hours max per night on it.

Places where I host my other images:

Flickr | Instagram

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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-290mc for guiding

• Moonlite Autofocuser

Acquisition: 21 hours 6 minutes (Camera at -15°C), NB exposures at unity gain and BB at half unity

• Ha - 99x360"

• Oiii - 83x360"

• R - 101x60"

• G - 100x60"

• B - 99x60"

• Darks- 30

• Flats- 30 per filter

Capture Software:

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

PixInsight Preprocessing:

• BatchPreProcessing

• StarAlignment

• Blink

• ImageIntegration per channel

• DrizzleIntegration (2x, Var β=1.5)

• Dynamic Crop

• DynamicBackgroundExtraction

duplicated each image and removed stars via StarXterminator. Ran DBE with a shitload of points to generate background model. model subtracted from original pic using the following PixelMath (math courtesy of /u/jimmythechicken1)

$T * med(model) / model

Narrowband Linear:

• Blur and NoiseXTerminator

• StarXterminator to completely remove stars (to be later replaced by the RGB ones)

• ArcsinhStretch to slightly stretch nonlinear

• iHDR 2.0 script to stretch each channel the rest of the way.

This is a great new pixinsight script from Sketch on the discord. here's the link to the repo if you want to add it to your own PI install.

RGB Linear:

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

• SpectroPhotometricColorCalibration

• BlurXTerminator for star sharpening

• HSV Repair

• StarXterminator to generate a stars-only image

• ArcsinhStretch + HT to stretch nonlinear (to be combined with starless narrowband image later)

Nonlinear:

• PixelMath to combine stretched Ha and Oiii images into color image (/u/dreamsplease's palette)

R = iif(Ha > .15, Ha, (Ha*.8)+(Oiii*.2))

G = iif(Ha > 0.5, 1-(1-Oiii)*(1-(Ha-0.5)), Oiii *(Ha+0.5))

B = iif(Oiii > .1, Oiii, (Ha*.3)+(Oiii*.2))

• NoiseX again

• Shitloads of Curve Transformations to adjust lightness, hues, contrast, saturation, etc

• LocalHistogramEqualization

• UnsharpMask

• More curves

• ColorSaturation to slightly desaturate the purples

• even more curves

• Pixelmath to add in the stretched RGB stars only image from earlier

This basically re-linearizes the two images, adds them together, and then stretches them back to before

(again, credit to Jimmy independent starless processing stuff)

mtf(.005,

mtf(.995,Stars)+

mtf(.995,Starless))

• Couple final curves

• DynamicCrop waaaay in on the nebula

• Annotation