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 2.6.4.5 (Win 10 ASCOM) using predictive PEC algorithm

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

Acquisition: Sequence Generator Pro 3.0.0.5

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.