3300 ± 900 LY

I was looking for a good target during nearly-full Moon that would benefit from narrowband filters. I have been wanting to try this one for some time since my last attempt was in 2015. After getting some OIII data that looked OK, I switched to Hα and immediately noticed a huge focus shift and brighter-than-expected stars. I surmised that the filter had probably come out of its slot in the filter wheel, so went on to get R, G, & B. When I took the filter wheel apart the next day the Hα filter had indeed fallen out along with one of its mounting screws. I found a number of other loose mounting screws, so snugged them up and put the Hα back. Processing this image was extremely challenging. I tried mixing various filters into the color channels, but I eventually opted to use OIII as L + HαGB synthetic L and HαGOIII for the color information. This gave stars that were quite green, so I had to reduce the green bias way beyond StarTools’ default. I attempted to image the core using unstretched 10- and 5-sec OIII and Hα, but this was only marginally successful; I don’t have the needed focal length (and probably don’t have the needed skill!). I can see some of the shape of the central part of the nebula. It was challenging to mix it in without making it look a mess. Overall, it’s better than my last attempt, although that’s not saying much. This is one of the most interestingly-structured planetary nebulae I have imaged; it looks like ink splashed on a photograph, leading me to wonder what caused all the knots and whorls. Wikipedia indicates that the central star is a Wolf-Rayet star, and that made a lot of sense to me as these tend to produce fascinating shapes in the surrounding nebula. So maybe this is more properly a wind nebula rather than a planetary.

Date: 8-9 May 2020
Subject: NGC 6543, Cat’s Eye Nebula
Scope: AT8IN+High Point Scientific Coma Corrector
Filters: ZWO 31 mm diameter unmounted 7 nm OIII, 7 nm Hα, R, G, B
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + ASI120MM-mini +PHD 2.6.7 (Win 10 ASCOM)
Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21
Acquisition: Sequence Generator Pro 3.1.0.457
Exposure: 48x300 OIII, 20x10 OIII, 48x300 Hα, 20x10 Hα, 30x180 R, 25x180 G, 30x180 B
Stacking: Deep Sky Stacker 4.2.3 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5
Processing: (I tried a lot of different approaches, and this is at least an approximation of what I finally settled on) StarTools 1.6.394RC: Combined OIII as L, Hα as R, OIII as G, & B in StarTools, accounting for exposure times to add in synthetic luminance. Software binned 2x2, cropped, gradient wiped, developed, HDR (optimize soft), slight deconvolution, color with large green bias reduction, untrack denoised (grain equalization). Several cycles of levels & curves, some layer-masked noise reduction. Stacked the 5-sec OIII and Hα in Nebulosity 4.4.1 (there weren’t enough common stars for DSS to stack them). Attempted (mostly unsuccessfully) to sharpen in StarTools and combined in Photoshop. Layered this nebular core onto the main image in Photoshop. AstroFrame.