I’ve had a long stretch of cloudy weather and just being busy, but got a bit of a break and decided to try the Angel Nebula. This is one of the more difficult targets I have attempted; it is quite dim and low in my sky. I also had a lot of problems with satellite trails. I had thought to work mostly with Hα with a little R, G, & B added in, but almost as an afterthought (well, I’d seen a lot of images with a lot of other colors) I decided to get some L as well. I’m really glad I did, because I think I got more detail from the L than from the Hα. Processing the color was a big problem because I stretched the color channels really hard and all kinds of flaws appeared without revealing much of the nebula. I therefore tried something new: I wanted to use Hα for the R channel without losing the authentic R for the stars, so I layered the two images in Photoshop with “Lighter color” as the blending mode. This kept the brighter stars from the R image but also brought in the nebulosity from Hα. I did something similar when combining Hα with L to produce the luminance that I actually used. Anyway, I worked to try and eliminate as many artifacts from the HαRGB and eventually did the color combination in StarTools. Back in Photoshop I used my HαL as a luminance layer with the HαRGB and this is the result. It doesn’t have as much detail as I would like, but given how low it always is on my horizon I guess it isn’t too bad.

Date: 26-30 Jan 2019

Subject: NGC 2170, Angel Nebula

Scope: AT8IN+High Point Scientific Coma Corrector

Filters: ZWO 31 mm diameter unmounted 7 nm Hα, R, G, B

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

Guiding: Orion Thin Off-axis Guider + DSI IIc +PHD 2.6.5dev6 (Win 10 ASCOM)

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

Acquisition: Sequence Generator Pro 3.0.3.151

Exposure: 11x600 Hα, 22x300 L, 8x300 R, 8x300 G, & 8x300 B

Stacking: Deep Sky Stacker 4.1.1 (64-bit) dark+flat (no bias), κ-σ stacking with κ = 1.5.

Processing: StarTools 1.4.332: Software binned all stacked images 2x2. Vignette wiped the Hα, Vignette wiped the L, Gradient wiped R, G, & B. Stretched and HDR optimized. Deconvoluted and untrack denoised the Hα and L. Just denoised R, G, & B. Took the pattern noise out of R using Carboni’s Astronomy Tools. Had to do extensive levels and curves on G & B along with a bit of clone stamp to get rid of things the flats didn’t fix. Used Photoshop to create HαR by layering with “Lighter color”, and used this as the R layer in the RGB, which I combined in StarTools and boosted the saturation. Created HαL the same way to use as L. Finally used HαL as L and (HαR)GB for color, adjusted levels yet again, AstroFrame