Before switching back to more well-behaved optics, given that it’s in the right place in the sky right now and that the ST80 has the right field of view, I couldn’t resist attempting M31 again. Because it’s so bright, I didn’t need as much integration as I’ve been accustomed to getting recently. Also, I’m playing with higher gain, shorter subs, and more of them as a way to improve my bit depth. This seems to work. This image presented a number of challenges, especially in processing. I don’t have autofocus capability on my ST80 yet (but I just took delivery of a stepper motor I think will fix that in the near future, with the added bonus that it should work on the MyFocuser Pro controller I have already built, as it’s the same motor I use on the AT8IN focuser with that controller). So that makes it hard to keep all the subs well focused, and I struggled to get good focus with both the L and the B data. I added in some Hα to try and make the Hα emission regions stand out a bit more, but I don’t really know how to add in the Hα effectively. I finally settled on adding it to the R channel and using some layer masking to allow it to show up only in the spiral arms where I think it should, but once again I’ve identified something I need to learn about. Overall, this image is far better than my best previous of this target, so I’m happy.

Date: 25-26 Sep 2017

Subject: M31, Great Andromeda Galaxy

Scope: Orion ST-80

Filters: ZWO 31 mm diameter unmounted Hα (7 nm bandpass), L, R, G, B

Mount: EQ-6 (EQMOD 2.000j)+PEC

Guiding: Orion Thin Off-axis Guider + DSI +PHD 2.6.4 (Win 10 ASCOM) using predictive PEC algorithm

Camera: ASI1600MM-Cool, -20 °C, Gain 200 Offset 50

Acquisition: Sequence Generator Pro 2.6.0.24

Exposure: 15x300 Hα, 60x180 L, 20x180 R, 19x180 G, 20x180 B

Stacking: Neb 4.1.6, flats & darks, trans+rot align, Nebulosity 1.5σ stack and align.

Processing: StarTools 1.4.328: Aggressively stretched and deconvoluted L. Combined R, G, and B in Nebulosity and also aggressively stretched the RGB. Used L as luminosity in Photoshop at 50% opacity. Mixed R and Hα using Linear Dodge (Add) in Photoshop, and used that for R channel but layer masked it so the Hα only shows in the spiral arms. Did several rounds of Levels and played with the saturation, desaturating B and G a bit to get rid of halos and star colors I didn’t like. A couple of repeats of Carboni’s Deep Space Noise Reduction. Finally, I used StarTools’ Lens module to try and compensate for aberrations around the edges somewhat. Astroframe.