These images are a combined 58-hours of exposure (Lum 15hrs; R 6.6 hrs.; G 6 hrs.; B 8 hrs; H-a 22 hrs). The Lums were 40 min subs 1X1; RGB 40 min. subs 2X2; H-a 1 hour subs 1X1 — just another day at the office! I added the 22 hrs of H-alpha to the Red channel. These were shot robotically and all are at -30C using the RCOS and Apogee U16M during April and May (pre-SN). You must wonder why I spent so much time capturing hydrogen-alpha data. Reason being, one of my all time favorite images of M51 was taken by a 1.23 meter telescope in southern Spain at Calar Alto with H-alpha data added big time (link below). I am not sure why they have so much green-yellow in their RGB image but I love the BOLD red-pink H-alpha in an RGBHa image they refer to as “a-new-look-into-the-whirlpool”. So I wanted to try to recapture some of that Calar Alto psychedelic H-alpha seasoning for my LRGB M51. They did 11 hours at 7nm bandpass; my H-alpha filter has a bandpass of 5nm. Nevertheless, I was not able to capture the incredible detail in H-a they got north of companion galaxy NGC 5195 (see the third image down on the link below). The two bright 17th magn. galaxies near M51 are IC 4277 (edge-on with yellow nucleus) & dumbbell-shaped elliptical IC 4278. Check out all the faint anonymous galaxies, especially clustered in the lower left corner and around the “bearded” tidal plume extending from the smaller galaxy NGC 5195! And see the varied galaxy morphologies at the top center which include a face-on spiral, edge-on, and tidally-distorted galaxies! The face-on galaxy seems to have a tiny adjacent galaxy (probably foreground) to its right. This main M51 galaxy also has detail right down to the stellar galaxy core.
http://www.caha.es/a-new-look-into-the-whirlpool-image-release.html — Examine “true” colour, RGBHa and H-alpha only images from Calar Alto, Spain – Fabulous!!