5500 ± 500 ly

I had some fun with this target. Looking for something appropriately placed in the sky and about the right size for my imaging train, I found Sh2-112 in my list of possibilities. When I went to save the imaging sequence in Sequence Generator Pro, I found I already had a sequence by the same name, which led me to look closer. I found I had already taken a goodly number of Hα subframes in 2018, but never finished collecting or stacking the data, and then forgot about it. So I took more Hα, added OIII and SII, and took some RGB as well. Playing with the processing was also fun. I was trying some different ways to run the stacking in Deep Sky Stacker and accidentally managed to stack all the Hα, OIII, and SII data together. Rather than throwing it away, I thought I might try using it as a luminance layer. I also did a straight up StarTools SHO combine, and found that using my combined stack as a luminance layer with that seemed to improve the image. Next I wanted to add in RGB stars, so I took a short set of RGB exposures (15 2-minute exposures with each filter) and did the RGB stack in StarTools. The default color module settings gave star colors I liked. I put this layer on top of the SHO with “all filter” luminance in Photoshop and used “Lighter color” to get RGB stars with SHO nebulosity. This did make my stars bigger, somewhat overwhelming the nebula, so I hit on the idea of using the original SHO layer again on top as a luminosity layer. This produced a result I liked, making the stars smaller without affecting the nebula. Finally, I usually play with turning the layers on and off to see what using them does, and was happy to see that if I turned off the bottom SHO layer—which I almost never try (leaving a “lighter color” RGB layer with the SHO luminance on top—I got a view of the nebula with the contrast of the SHO but the RGB colors. Liking this, I kept it too. I think there’s probably a little more structure-revealing contrast in the Hubble palette version, but it’s a close call (and I’d love to hear others’ opinions). I saw a pretty wide range of distance estimates for Sh2-112, so I went with a rough average.

Date: 26-27 Jun 2018, 22-24 Jun 2020
Subject: Sh2-112
Scope: AT8IN+High Point Scientific Coma Corrector
Filters: ZWO 31 mm diameter unmounted 7 nm bandpass Hα, OIII, and SII; R, G, B
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + ASI120MM-mini +PHD 2.6.8 (Win 10 ASCOM)
Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21
Acquisition: Sequence Generator Pro 3.1.0.479
Exposure: 71x300 Hα, 30x300 OIII, 30x300 SII, 15x120 R, 15x120 G, 15x120 B
Stacking: Deep Sky Stacker 4.2.3 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5
Processing: StarTools 1.6.394RC: Composed Hα, OIII, and SII in StarTools accounting for exposures to create a synthetic luminance. Software binned 2x2, cropped, and vignette wiped. Developed at 94%, HDR (reveal all), deconvoluted and untracked denoised (grain equalization). Composed R, G, & B accounting for total integration times in creating a combined synthetic luminance. Software binned 2x2, cropped, vignette wiped, developed (94%), HDR (reveal all), deconvoluted slightly, ran the color module with default settings, and untrack denoised (grain elimination). In Photoshop, played with things as described above. AstroFrame.