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Imaging telescope or lens:Tamron Adaptall 135mm F2.8
Imaging camera:ZWO ASI1600MM-Cool
Guiding telescope or lens:Orion 9x50 finder
Guiding camera:Meade DSI II C
Software:EQASCOM, photoshop, Nebulosity, Noel Carboni's Astro Tools for PhotoShop, Enterprise Astronomy Annie's Astro Actions, Sequence Generator Pro, PHD2 Guiding, Silicon Fields StarTools 1.3, AstroPlanner
ZWO Blue 31 mm: 25x10" (gain: 139.00) -20C bin 1x1
ZWO Green 31 mm: 25x10" (gain: 139.00) -20C bin 1x1
ZWO Green 31 mm: 19x120" (gain: 139.00) -20C bin 1x1
ZWO H-alpha 7nm: 31x300" (gain: 139.00) -20C bin 1x1
ZWO OIII 31 mm 7 nm: 24x300" (gain: 139.00) -20C bin 1x1
ZWO Red 31 mm: 25x10" (gain: 139.00) -20C bin 1x1
Integration: 5.4 hours
Avg. Moon age: 25.87 days
Avg. Moon phase: 14.55%
Astrometry.net job: 1891402
RA center: 85.096 degrees
DEC center: -2.741 degrees
Pixel scale: 5.936 arcsec/pixel
Orientation: 87.545 degrees
Field radius: 4.712 degrees
Locations: Mapleton Lateral Observatory, Mapleton, Utah, United States
I wanted to compare what I can do now with the image I took of this area last year, which was my first try at SHO Hubble Palette imaging and one of the first using the Tamron 135 mm f/2.8 lens. I had a very hard time processing the data for this image, but I felt this beautiful region of the sky deserved my best effort so I spent a lot of time on it. Trying to get the colors where I wanted them was particularly hard. I took a lot of R and B frames I did not use because the RGB image just didn't look very good. I wanted the Hα behind the Horsehead Nebula and the Flame Nebula to show different colors, but when I applied the Hα as luminance that was consistently getting messed up. What finally worked was to make a HαGO combination (Hα is definitely in the red region, I don’t have anything else for G, and OIII is definitely blue. The B filter produces terribly bloated stars, because apparently this lens doesn’t focus well across the range of the filter, so I used the narrowband filter to get much better-looking stars). I used Hα as luminance, then layered the HαGO back on top with “Pin Light” blending mode at 50% opacity to bring back the correct colors. Finally, I layered an RGB image using 10 s subs on top with a hide all layer mask, and put holes in the mask for central M42 and for some of the more prominent stars to get rid of overexposure and to correct the color for those brighter stars. I think the result is far superior to last year’s effort. Oh, and I almost forgot this is first light for use of my “new” used Windows 10 desktop computer to control the session. In many ways it’s simpler than using VMWare on a Mac, but some of the camera connection stability issues I was hoping to get rid of still persist.
Date: 12-13 Jan 2018
Subject: Orion Molecular Cloud Complex
Scope: Tamron 135 mm f/2.8 lens stopped to f/4
Filters: ZWO 31 mm diameter unmounted Hα, SII, OIII (7 nm bandpass), R, G, B
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion 9x50 Finder/Guider + DSI IIc +PHD 18.104.22.168 (Win 10 ASCOM) using predictive PEC algorithm
Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21
Acquisition: Sequence Generator Pro 22.214.171.124
Exposure: 31x300 Hα, 19x120 G, 24x300 OIII
Stacking: Neb 4.1.6, dark+flats, trans+rot align, Nebulosity 1.5σ stack and align.
Processing: StarTools 1.4.328: Used StarTools’ “Wipe” module to correct for vignetting remaining after flat correction, then aggressively stretched and deconvoluted each channel separately in StarTools. Aligned the processed layers in Nebulosity then combined in Photoshop using Annie’s Astro Actions’ RGB module with Hα assigned to R, G in G, and OIII in B. I used Hα as luminance, then layered the HαGO back on top with “Pin Light” blending mode at 50% opacity to bring back the correct colors. Finally, I layered an RGB image using 10 s subs on top with a hide all layer mask, and put holes in the mask for central M42 and for some of the more prominent stars to get rid of overexposure and to correct the color for those brighter stars. Did quite a lot of work to get rid of reflection/halos around the brighter stars. Played with the color balance to “de-green” just a tad, and darkened slightly with Levels. AstroFrame.
These are the same data except here I’ve got the SHO Hubble Palette version where obviously I’ve used SII rather than G and mapped the colors quite differently using Annies Astro Actions. This was a lot easier to process than the attempt at true color above. It’s amazing how much different M42 appears to be chemically from the rest of the nebulosity, where Hα seems to be heavily dominant; there’s quite a lot of SII and OIII showing up in M42. I guess this is the version that really should be compared with last year’s effort, which was also SHO. I think I’ve learned a little since then.
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