Sh2-155 or more commonly known as the Cave Nebula is a complex region in the constellation Cepheus that contains emission, reflection, and dark nebulae. The most eye-popping part is the ionized hydrogen (Ha) region which supports star formation approximately 2400 light-years away. It also happens to lie at the edge of the much larger Cepheus Molecular cloud so it is plenty dusty! To make things more interesting there is a less popular reflection nebula nearby in Cepheus known as Ced 201 or VdB 152 which also goes by the nickname the Cave Nebula. Patrick Moore included Sh2-155 in his catalog as Caldwell 9 but also nicknamed it the Cave Nebula even though Ced 201 was previously nicknamed the Cave Nebula.

This was the fourth time for me on this object and the second time using the SHO palette. The other two were widefield and with the dual band filter. This narrowband SHO image came out much better than my first attempt partly due to better filters and better processing techniques. The Antlia 3nm filters just bring out the fine detail more than the capable 7nm filters I was using. I probably could have brought out the surrounding nebulosity amore but I like the fading translucent look.

I had some issues with WBPP in PixInsight when stacking as it left stripes running down the SII and OIII stacked images. I remade flats and darks and did a bunch of experiments before I zeroed in on PI where I posted the issue on the forum as well as the Facebook page. The answer from a PI Top Contributor (Vicent) was I needed to 'deactivate the Linear Correction under the Lights tab'. Apparently it is not needed for CMOS cameras. I also had issues with using the EZ Processing suite, in particular I had been using the EZ Soft Stretch scripts as part of my normal routine. However, Dark Archon, the developer, had other commitments so were not usable for a time. Looking for a new easy way (I am lazy) to stretch linear data I came across Bill Blanchan's Pixel Math scripts which I used here (HT Stretch Unlinked). He wrote back with directions on how to reinstall the EZ Processing suite if I wanted to still use it. As of this writing I like Bill's method better.