I’ve always thought M33 is a beautiful galaxy. It’s close enough you can see a lot of what is going on, and it has lots of pretty star-forming regions and clusters of bright young blue stars. This is the first time I’ve been able to pick up some of the faint outer arms, and it was worth it to use the extra integration. After doing most of the acquisition with 180-s subs at a gain of 200, I added more luminance with 300-s subs at unity gain (139 on this camera). The latter are what really picked up the outer arms. I thought about adding some Hα to further enhance the star-forming regions, but after seeing the RGB decided they already show up pretty well. The sky was especially clear for the data that make up this image. Much better than my last previous attempt. This monochrome LRGB stuff is hard (i.e. more fun to process!) but produces nicer results than I was ever able to get with a one-shot color camera.

Date: 27-29 Oct 2017

Subject: M33, Triangulum Pinwheel Galaxy

Scope: AT8IN + High Point Scientific coma corrector

Filters: ZWO 31 mm diameter unmounted L, R, G, B

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

Guiding: Orion Thin Off-axis Guider + DSI +PHD 2.6.4.4 (Win 10 ASCOM) using predictive PEC algorithm

Camera: ASI1600MM-Cool, -20 °C, Gain 198 Offset 50 (with some L done at Gain 139 Offset 21)

Acquisition: Sequence Generator Pro 3.0.0.2

Exposure: 71x180 L 30x180 R, 30x180 G, 30x180 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 in StarTools. Combined RGB in Neb 4 and stretched, color balanced, deconvoluted (less aggressively) in StarTools. Gradient Xterminator. Several rounds of layer-masked levels to try and get rid of color gradients, followed by several rounds of layer-masked desaturation for the same purpose. Several rounds of “Increase Star Color.” AstroFrame.