During my May 2021 trip to Namibia my imaging plan was not limited to narrow field with a 10-inch ASA astrograph: I also took wide-field pictures with by Baader-modified 6D DSLR.
My wide-field program’s main goal was the vast nebular complexes of constellation Vela and Puppis, which offer good visibility conditions in the evening sky, thereby leaving enough time to image this wonderful area of the southern sky. The Vela nebula, better known as the Gum Nebula, is actually made up of different objects, of which the most prominent are:
The so-called “Vela Molecular Ridge”, located in the northeastern part of the complex, containing the nebula’s brightest H II regions, namely: Gum 14 (RCW 27), Gum 15 (RCW 32) e Gum 17 (RCW 33);
The central portion of the Nebula, which contains a vast “mesh” of filaments that are thought part of a supernova remnant.
The Gum Nebula covers an overall area of more than 10 degrees, which requires a very wide field rig: my 6D and my Samyang f/2 lens make up a suitable combo, covering a field of about 10 x 15 degrees. In order to capture the nebula’s delicate H-alpha wisps, I also used an EOS-clip H-alpha filter from Optolong, which is hard to come by and now discontinued, but luckily I managed to get hold of one. Although color cameras are not ideal for narrowband imaging, as we are going to see shortly, the Optolong filter allowed yielded a much higher contrast and detail in the final composite.
Let’s now move on to the photos, all of which resulted from the stacking of 10-min (15 mins for H-alpha) subs at 1600 ISO atop a Fornax 51 mount. For autoguiding I used a Staraid rev. B stand-alone camera, the latest version of the one I used back in 2019 (detailed review available at this link), or an ASI 224 MC. All wide-field imaging was done with a Raspberry Pi 4 running Astroberry Server, a version of Raspbian (Raspberry Pi’s Linux flavor) optimized for astronomical imaging,
Let’s start off with this article’s highlight, the Gum Nebula. First is an HaRGB version resulting from 37 x 10 mins subs for RGB and 17 x 15-min subs for H-alpha, for a grand total of 625 mins, i.e. more than 10 hours. In order to better show the delicate and intricate structures of the nebula, next comes a mono H-alpha version with all stars removed through PixInsight;’s Starnet2 process.
Let’s continue our journey with another wide-field shot, once again taken with the 135-mm lens. In this case it’s an area encompassing part of constellations Ara and Norma. The H-alpha nebula in the lower part of the frame is NGC 6188+NGC 6193. 60 x 10 min subs ( about 10 hours) were taken for this shot.
I also used a longer focal length, which still belongs to the wide-field category, my Canon 100-400 L IS II zoom lens at its longest focal length. As an aside, PixInsight’s plate-solve script showed that the maximum focal length is not 400 mm but a bit shorter, about 385 mm to be precise. I took two pictures at this focal length: IC 4628, the so-called “Prawn Nebula”, and the area of Chamaeleon’s vast molecular clouds, of which IC 2631 is the main feature. These two shots are the result of 29 x 10 and 30 x 10 minutes respectively, i.e. about 5 hours of total exposure each.
A big thanks to Edoardo Radice for his invaluable support in my never ending quest to tame PixInsight :-)