The Cygnus Loop, also known as the Veil Nebula, is a large supernova remnant in Cygnus. Its wispy filaments that stretch across the sky make it a very appealing target for beginner and expert astrophotographers alike. Due to the rich colors emitted by HII, OIII, and SII, images of this object benefit heavily from filters. That is why after I received my Optolong L-eNhance filter, the first target I had on my mind was the veil.
What is the Veil Nebula?
The Veil nebula is a large supernova remnant in the northern constellation Cygnus. A supernova occurs when matter in a star collapses in on itself, causing a huge release of energy, blasting the outer layers of the star away at super fast speeds. Those outer layers usually contain atoms like hydrogen, oxygen, and sulfur, along with other atoms created during the supernova. Atoms like those are what we see when looking at supernova remnants like the Cygnus Loop, Vela remnant, and even the Crab nebula.
The Vela Supernova Remnant Credit: ESO/J. Perez
The Optolong L-eNhance 2"
The L-eNhance is a multi-bandpass filter. That means that instead of just showing light like H-alpha or OIII, it collects light from both wavelengths. This is very useful to astrophotographers because many nebulae contain gases like hydrogen and oxygen that emit those wavelengths of light. Because the filter only allows specific light to pass, it almost completely stops wavelengths that are commonly found in streetlights and other forms of light pollution, making the L-eNhance an excellent option for those in light polluted cities and suburbs who want to capture targets that would normally be very challenging from their location.
There is a complaint that many have including myself, and it has to do with star color. For example, if you are using the L-eNhance, most stars will appear white. This is not a problem if you reshoot your target without the filter and make a star mask with the regular colors, though. For an affordable price, the L-eNhance is one of the best filters you can get to improve your astrophotography.
Optolong L-eNhance 2" filter
Other gear
Also used to take the image were the Sony a6000, Redcat 51, and HEQ5 pro. There is more information about this gear in the My Equipment section of the page.
Data Acquisition
In order to photograph the Cygnus Loop in detail, it is required to take long exposure images. These can stretch from 30 seconds to hours per sub. Once tens to hundreds of long exposures are taken, they are stacked together to form one image with detail and less noise. For the Cygnus Loop, I chose to take 61 three minute long images, as well as another 48 minutes for calibration frames, leaving my total exposure time at 231 minutes, just under 4 hours. This is by far the most data I've collected on a single target, and it payed off. After processing the image, I believe it is the best photo I've taken so far, and I hope you feel the same way.
Processing
In order to bring out as much detail as possible from a photo, it is necessary to stack images together and make other adjustments to the data using applications like Photoshop, GIMP, and other image processors.
The software I use to stack images is SiriL. It does a very good job of stacking, but it also has features that help when post-processing. In order to stack the subs together, I used the OSC_Preprocessing script that automatically stacks the light frames, darks, flats, and biases together. After it is done stacking, it saves the stack so you can do other edits to it.
While still in SiriL, I did a background extraction of the image to eliminate unnecessary color in the background. After this, I did a photometric color calibration to the image. This corrects the color of the image so the nebula and stars look natural. After the edits in SiriL, I moved the image over to GIMP. While in GIMP, I stretched the image to reveal the data I had captured. After adjusting the colors to my liking, I put the image through a software called starnet++. This software takes all of the stars out of the image and leaves just the nebula, so you can edit the nebula without blowing out the stars.
Starless Cygnus Loop
After getting the nebula layer back into GIMP, I did another stretch to bring out even more detail in the faint wisps. After I was happy with that, I made a mask of just the stars, and put that over the nebula image. Finally, after processing the image, I have this image. Enjoy
The Cygnus Loop by Me
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