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Imaging telescope or lens:Astro-Tech AT8IN
Imaging camera:ZWO ASI1600MM-Cool
Guiding telescope or lens:Astro-Tech AT8IN
Guiding camera:ZWO AS120MM-Mini
Software:Noel Carboni's Astro Tools for PhotoShop , StarTools , AstroPlanner , PHD2 Guiding , Sequence Generator Pro , EQASCOM , DeepSkyStacker , photoshop , Enterprise Astronomy Annie's Astro Actions
ZWO Blue 31 mm: 20x120" (gain: 139.00) -20C bin 1x1
ZWO Green 31 mm: 20x120" (gain: 139.00) -20C bin 1x1
ZWO H-alpha 7nm: 55x300" (gain: 139.00) -20C bin 1x1
ZWO Luminance 31 mm: 60x120" (gain: 139.00) -20C bin 1x1
ZWO OIII 31 mm 7 nm: 20x300" (gain: 139.00) -20C bin 1x1
ZWO Red 31 mm: 20x120" (gain: 139.00) -20C bin 1x1
ZWO SII 7nm: 17x300" (gain: 139.00) -20C bin 1x1
Integration: 11.7 hours
Avg. Moon age: 14.63 days
Avg. Moon phase: 2.33%
Bortle Dark-Sky Scale: 5.00
Astrometry.net job: 3303452
RA center: 7h 29' 1"
DEC center: +13° 15' 14"
Pixel scale: 1.719 arcsec/pixel
Orientation: 89.528 degrees
Field radius: 0.682 degrees
Locations: Mapleton Lateral Observatory, Mapleton, Utah, United States
Data source: Backyard
I saw I had not tried this target in 4 years and was looking for something that would work well in narrowband, so thought I’d try the Medusa Nebula. I was fighting my focuser trying to get the tension properly adjusted, so had a hard time getting good focus on the first subframes I took. Not fully satisfied with the early result, I decided to integrate some more and I’m glad I did. I took LRGB data primarily intending to use it for star colors and was interested to see that the nebula itself is pretty dim; the narrowband filters helped a lot, especially Hα although the nebula showed up in all 3 filters. Processing was also a struggle this time. I found I needed to do levels & curves on the nebula after adding an Hα luminance layer but before using a “lighten” combine to add in the LRGB stars. I processed both an SHO Hubble palette version and a HSO version; once again, I think the chemical differences in the nebula show up better in the Hubble version so that’s the one I prefer. It’s interesting that Wikipedia describes this as a planetary nebula. If that’s indeed correct, it’s an unusually structured one.
Date: 21-25 Feb 2020
Subject: SH2-274, Medusa Nebula
Scope: AT8IN+High Point Scientific Coma Corrector
Filters: ZWO 31 mm diameter unmounted 7 nm Hα, SII, OIII, L, 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 188.8.131.522
Exposure: 55x300 Hα, 17x300 SII, 20x300 OIII, 60x120 L, 20x120 R, 20x120 G, 20x120 B
Stacking: Deep Sky Stacker 4.2.3 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5.
Processing: StarTools 1.6.387: For Hα, SII, & OIII each, software binned 2x2, cropped, developed, HDR “reveal all”, deconvoluted, and untrack denoised (grain equalization). Combined L, R, G, & B in StarTools, adjusting for exposure times. 2x2 software binned, cropped, developed, HDR “reveal all,” color module with heavy saturation boost and that barely made the color show up. Untrack denoised (grain removal). In Photoshop, used Annie’s Astro Actions to do SHO Hubble combination, attempting to overlap the histograms for the 3 colors as much as possible. Did the same using the RGB action to do HSO. For both SHO and HSO, applied Hα as luminance and did some levels & curves adjustments. For the LRGB, used Astronomy Tools’ “increase star color” and “decrease star size,” then combined with the SHO and HSO using “lighten.” More levels and curves. AstroFrame.
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