Sh2-155 aka Caldwell 9 aka The Cave Nebula

The Cave Nebula

The Cave Nebula in Cepheus

The Cave Nebula, Sh2-155 or Caldwell 9, is a dim and very diffuse bright nebula within a larger nebula complex containing emmison, reflection, and dark nebulosity. [Wikipedia]

Here is the RGB image without the H-Alpha added:

The Cave aka Sh2-155 aka Caldwell 9

Scope: Planewave 12.5" CDK
Camera: Apogee U16M w Astrodon GenII H-Alpha filter
Mount: Paramount ME guided w Astrodon MMOAG and SBIG ST-402ME
36 x 20 min of H-Alpha
11/7/14 x 10 min each of RGB
Acquired with TheSkyX and CCD-Commander

PixInsight processing:
RGB: CombineChannels, SPCC, BlurX, NoiseX, Curves, HistogramTransformation, Saturation Boost, save as TIFF
H-Alpha: BlurX, NoiseX, StarX, Curves and HT on the starless image, 2xLocalHistogramEqualization (for contrast), save as TIFF

Photoshop processing:
RGB split into channels, cleanup of some odd artifacts, starless H-Alpha added to Red at 100% and to Blue at 20% using Lighten Blend mode. Recombined the channels. Adjusted colour using Selective Colour (drop Cyan in the red channel) then some spot cleanup and curves. Save for Web

Lucknow, Ontario
October 2023