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M81 & M82, Bode's Galaxies, HαLHαRGB, 4 & 11 May 2017

Technical card

Resolution: 4377x3330

Dates: May 4, 2017May 11, 2017

ZWO Blue 31 mm: 12x300" -20C bin 1x1
ZWO Green 31 mm: 12x300" -20C bin 1x1
ZWO H-alpha 7nm: 14x600" (gain: 139.00) -20C bin 1x1
ZWO H-alpha 7nm: 4x600" -20C bin 1x1
ZWO Luminance 31 mm: 36x300" -20C bin 1x1
ZWO Red 31 mm: 12x300" -20C bin 1x1

Integration: 9.0 hours

Avg. Moon age: 11.56 days

Avg. Moon phase: 79.70% job: 1578444

RA center: 148.924 degrees

DEC center: 69.294 degrees

Pixel scale: 0.860 arcsec/pixel

Orientation: 88.078 degrees

Field radius: 0.657 degrees

Locations: Mapleton Lateral Observatory, Mapleton, Utah, United States


At the risk of posting two very similar images back-to-back, I added some Hα data to this year’s Bode’s Galaxies image. After shooting a few 600-s frames at the “0” (maximum dynamic range) setting, I decided I just wasn’t getting enough signal to a switched to unity gain (the “139” gain setting) and was more satisfied. Processing this was difficult. I used a 50/50 mix of the original R channel with the Hα for R, then mixed in little Hα with L to create a new L. The difficult part came when I attempted to get the color balance right. There was certainly nothing scientific about it. I used a lot of layer masking with color balance tweaking and also worked hard to make sure the “jets” coming out of M82, which are most prominent in Hα, were visible. I was pleased to see some of the Hα emission regions in M81 also showing up. A better image will have to wait until next season.

Date: 4 & 11 May 2017
Subject: M81 & M82, Bode’s Galaxies
Scope: AT8IN + High Point Scientific coma corrector
Filters: ZWO 31 mm diameter unmounted L, R, G, B, Hα
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + DSI +PHD (Win 10 ASCOM) using predictive PEC algorithm
Camera: ASI1600MM-Cool, -20 °C, Gain 0 Offset 10, some with Gain 139 Offset 21
Acquisition: Sequence Generator Pro
Exposure: 36x300 L, 12x300 R, 12x300 G, 22x300 B, 20x600 Hα
Stacking: Neb 4.1.5, flats & darks, trans+rot align, Nebulosity 1.5σ stack and align.
Processing: StarTools 1.4.327. Stretched and deconvoluted the luminance. Combined RGB in Neb 4 and stretched, color balanced, and sharpened in StarTools. Layered luminance over RGB in Photoshop CC 2014, boosted the vibrance a lot and saturation a little. Applied GradientXTerminator medium/high. Layered RGB on top of the LRGB as a color burn at ~40%, then masked out the galaxies and gaussian blurred the mask. Mixed 50% R from this with 50% Hα and used that as the final R. Mostly used the original L, but to make the jets of M82 show up I added some Hα to the luminance in the area of M82. Then lots of layer-masked color adjustment to make the Hα show up well without making the galaxies or the background look too nasty. Topped off with AstroFrame



David Dearden

Sky plot

Sky plot


M81 & M82, Bode's Galaxies, HαLHαRGB, 4 & 11 May 2017, David Dearden

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