This has been a very difficult object for me. Probably I need darker skies than I have here in Mapleton (I tried 300 s luminance subs, had way too much sky glow, cut it back to 180 s, and still had quite a bit), and I just seem to have a more difficult time with LRGB these days than with narrowband (Narrowband is truly magic!). This kind of faint reflection nebula also seems to be the most difficult type of target for me. Then to make this even more difficult, leaving a star as bright as Rigel in the field of view presented all kinds of challenges, but I wanted it there because I understand Rigel is thought to light up the nebula. Finally, the Tamron lens does seem to perform less well with the blue filter for some reason, requiring a lot of star shrinking in the blue channel to avoid nasty rings around the stars. I’m still struggling a little to get good flats, though my L and R flats weren’t too bad this time (I think I’m probably exposing them too much so they overcorrect). Gradient Xterminator was a huge help, along with Carboni’s Soft Color Gradient Removal action. Of interest to me were the satellite trails that appeared in nearly every subframe; two parallel trails that appear and disappear as if the satellite is slowly tumbling. I’m guessing these must be geosynchronous or at very least in high, nearly equatorial orbits. They appeared frequently enough in the same places that sigma-clip stacking did not eliminate them, and I left them in (running vertically through the Witch’s chin) because they really were in that part of the sky.

Date: 12-15, 22 Dec 2017

Subject: IC 2118, Witch Head Nebula

Scope: Tamron 135 mm f/2.8 lens stopped to f/4

Filters: ZWO 31 mm diameter unmounted L, R, G, B

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

Guiding: Orion 9x50 Finder/Guider + DSI IIc +PHD 2.6.4.5 (Win 10 ASCOM) using predictive PEC algorithm

Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21

Acquisition: Sequence Generator Pro 3.0.0.4

Exposure: 98x180 L, 41x180 R, 24x180 G, 31x180 B

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

Processing: StarTools 1.4.328: Used StarTools’ “Wipe” module to correct for gradients the flats didn’t get, then stretched each channel separately in StarTools. Deconvoluted the L channel. Aligned the processed layers in Nebulosity then combined in Photoshop using Annie’s Astro Actions’ LRGB module. Stretched some more in Photoshop using Curves and Levels. Gradient Xterminator + Carboni’s Soft Color Gradient Removal, combined with several rounds of Carboni’s Make Stars Smaller, then Deep Space and Space Noise Reduction. AstroFrame.