One of the first objects that I shot when I got my first telescope (an 8" SCT with Hyperstar) was M51. Looking back, it was a blurry mess... But I was so excited with it! I couldn't believe that I was able to actually photograph something that was 31mly away.
I have re-imaged this galaxy 3 times since then, but this time I really wanted to make sure that I did justice to the tidal streams surrounding this awesome pair. And I wanted to make sure that the arm of M51a crossing in front of M51b looked like it belonged to M51a, and did not "melt" into the dwarf galaxy behind. I'm sure I hit the first goal, and I think I hit the second, but I would like to hear your thoughts...
I also wrestled with the saturation on this image. I think I tend to prefer over-saturated images, so I really tried to pull back on the saturation of this one. Again, I would appreciate your thoughts.
Finally, I took some real time on the Ha portions of this object. First, I performed a continuum subtraction (see Vincent Peris' article
Messier 31 Ha Processing Notes for the method) so that (as best as I could) I was only dealing with the Ha emission. I also removed any remaining leftovers from stars in the image. Knowing that Ha is 656nm, I found the R, G, and B components for this emission line, which are R = 0.4510, G = 0.0039, and B = 0.1216. I then used this PixelMath expression:
R: $T + ((H_cs - med(H_cs)) * k * 0.4510)
G: $T + ((H_cs - med(H_cs)) * k * 0.0039)
B: $T + ((H_cs - med(H_cs)) * k * 0.1216)
where $T was the LRGB image, H_cs is the continuum subtracted Ha image, and k is a scale factor that I tweaked until I found the right balance. I was pleased with the results but, again, appreciate your feedback.
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