The Pacman Nebula (NGC 281)
The Pacman Nebula is a large emission nebula that is approximately 48 light years across and nearly 9500 light years from earth. It was named for its resemblance to the popular Pac-Man character in video games, although you’ll probably have to use your imagination to see this in my image (Pac-Man is facing towards the top of the image). Unlike the the popular Namco mascot, this Pac-Man does not gobble up dots, it is actually creating them; NGC 281 is a star forming region that lies near the constellation Cassiopeia.
Collecting the data
Miguel, who is now getting serious into deep sky object (DSO) photography, and I met at what is now my favorite location for this work – Danville Conservation Area in Montgomery County, MO. This is classified as a Bortle 4 sky location and we were working under near perfect conditions of a new moon, no clouds, low winds and cool temps (mid to low 40s). Selecting a great night was one of the successes of this project. Miguel was just beginning to work on his new rig, attempting polar alignment for the first time and trying out his more sophisticated system of go-to and guiding. I use a simple unguided star tracker and the camera gear I use for normal daytime photography and had my target in mind and planned a night of imaging.
Canon 7d mkii, 300mm f/2.8 lens is mki, Sky-Watcher Star Adventurer tracking mount with extra counterweight balance, Bahtinov focus mask, red-light scope, heat packs used for prevention of dew formation on lens, all setup on a sturdy Gitzo carbon fiber tripod and anchored to a concrete block.
Lights: Approximately six hours with 30 second subs (manually removed obvious bad subs and used 512 subs for integration.
Darks: 32 darks captured in field after imaging
Flats: 40 flats taken the next day from home
Bias: 67 bias images
Image shown here was stacked using Sequator. Stacked file was processed in PhotoShop CS6, manually following processes described in various YouTube videos. See below for details learned from this processing session.
Problems and learnings
This was a good night but definitely not perfect. Again, I struggled with getting proper polar alignment. My main issue was not identifying Polaris, necessarily, as we were easily able to find it with our naked eyes. The problem came from being able to correctly identify the star while looking through the reticle. Ultimately, I picked the most likely candidate and went with that. I didn’t have much star trailing in my 30 second subs, so I think I did an OK job. I did notice that the tracking was off and I had to recenter the target about once an hour, but that is due to using an unguided tracker and the weight of my rig. This is something I’ll just have to remember to do with future objects.
I have picked up a couple pieces of gear that will dramatically help with achieving proper PA on future projects. First, I purchased a green laser pointer that I can shoot directly through the reticle and line up perfectly with Polaris. More importantly, I finally picked up a new wedge/base mount to support the tracker. This is the piece that is critical in getting proper PA. The mount that comes with the Sky-Watch Star Adventurer is severely lacking in many ways and is frankly a POS. The William Optics model I now have (see photo) is all metal, allows for more precise control in declination and is much easier to control right accession with. The differences are like night and day! I didn’t have these two things for imaging NGC 281, but I have them now and tried them in the yard one night and achieved perfect polar alignment in less than 15 minutes! I feel much less anxiety about this step now and wish I hadn’t waited so long to pick up this base mount.
The biggest mistake of the night was something I was aware of but simply forgot to handle. I left the settings for auto orientation on in the camera. This means, as the mount tracked the object over the course of the night, about half of my images were in the horizontal orientation and half of them were in the vertical orientation. This is a much bigger problem than it seems. In most software, you can change the orientation of an image with a simple mouse click. However, the orientation is actually embedded in the exif data of your RAW files. I came to find out that most stacking programs will not orient all of the files for you and, therefore, I was losing half of my light subs in the stacking process. It is possible to change the exif data to make them all the same, but this requires computer skills that I simply do not have. Thankfully, Sequator did accept all of my subs, but it is not the best software for stacking DSOs. I would love to fix this in the data I have collected for NGC 281 and be able to stack in Deep Sky Stacker or ASTAP one day, but I will definitely remember to turn this function off in camera in the future.
Processing after stacking was the usual barrel of fun. I found it a little easier than I did for M31, but I think I have a long way to go. I was hoping to get much more detail in NGC 281. I think I had ample integration time and feel there may be some detail I can pull out with better processing. Maybe the fault lies in my images themselves and I could do better with PA and tracking. It might also have to do with the focal length. With the 480mm focal length equivalent used for this object, I don’t have much more opportunity to improve here, but I could have used a 1.4x teleconverter and get 672mm focal length equivalent. I think there was room to do this with this object, but I would have had to recenter more often and lost some light gathering in the process. Maybe next year!
Despite the final outcome, which I am satisfied with, this was a lot of fun. I’m finding that I can have fun doing almost anything as long as I am outside. This is getting truer all the time. Although this process has its frustrations and anxieties, I guess you can call that a “good stress.” I’ll always remember the pair of Barred Owls squawking away at each other and the coyotes howling and barking on at least three sides from where Miguel and I worked. In addition, while I was breaking down at about 3:00 am, two armadillos noisily burst through the grasslands, coming up to within ten feet of me to see what I was doing.
My hope is to continue this and image one object a month. I think I can sacrifice one good night’s sleep a month for such experience, learning and memories.