This is part of a continuing effort to learn narrowband astrophotography and to try and go a bit deeper than in the past. I was surprised at how this image turned out when I finally got all the data and did the SHO combination. It probably helped that my expectations were not very high. When I originally stacked the data from each filter I knew this area lit up well in Hα, and was a little surprised to see as much SII as was present, but was equally surprised at how little OIII emission was visible in my OIII stack. So when I put them together I was astonished to see so much blue and such a range of colors. This was really fun to assemble. Another unusual thing about this image was that somehow I accidentally switched on 2x2 binning while acquiring the Hα data. I collected the other channels 1x1, but binned them in processing (which of course drastically sped up the processing steps). So I gained some bit depth and lost some resolution as a result. This image is dramatically better than any of my previous attempts on this target.

Date: 6, 7, 12 Oct 2017

Subject: Sh2-155 (Cave Nebula)

Scope: AT8IN + High Point Scientific coma corrector

Filters: ZWO 31 mm diameter unmounted SII, Hα, OIII (7 nm bandpass)

Mount: EQ-6 (EQMOD 2.000j)+PEC

Guiding: Orion Thin Off-axis Guider + DSI +PHD 2.6.3.7 (Win 10 ASCOM) using predictive PEC algorithm

Camera: ASI1600MM-Cool, -20 °C, Gain 198 Offset 50

Acquisition: Sequence Generator Pro 3.0.0.2

Exposure: 78x300 Hα, 96x300 SII, 96x300 OIII

Stacking: Neb 4.1.6, flats & darks, trans+rot align, Nebulosity 1.5σ stack and align.

Processing: StarTools 1.4.328: Aggressively stretched and deconvoluted each of the 3 channels in StarTools; binned the SII and OIII 2x2 in software whereas Hα was acquired in 2x2. Aligned the processed layers in Nebulosity then combined in Photoshop using Annie’s Astro Actions’ Hubble Palette module. Used the Photoshop Channel Mixer to adjust the colors a little, then did a little layer-masked Levels work to get rid of some unwanted red cast. Did a little Curves & Levels in Photoshop, along with deep space and space noise reduction followed by “less crunchy more fuzzy.” AstroFrame.