During the most recent new moon, I finally took out my star tracker and kit to try my hand at photographing a deep sky object (DSO) for the first time. I knew this was going to be challenging and this first attempt would be more for learning than producing an image that I would be excited about. However, thankfully it was both – it was a beneficial experience in that I got practice in all the process surrounding making an image of this sort (I will go into details below), and at the same time the final image turned out better than I expected, especially considering the challenges I had. For those of you who don’t care about the process, you can stop reading here – I won’t blame you. For those of you interested, I will provide some of my notes and things learned. You can tell me if it was worth the hassle or not.
The Andromeda Galaxy (M31)
The Andromeda Galaxy is also known as Messier 31 and NGC 224. It is classified as a barred spiral galaxy and is about 2.5 million light-years from earth. It is the largest galaxy in our local galaxy group and is on a direct path to merge with our Milky Way in about 4.5 billion years.
Did you notice? In this image there is more than just the M31 galaxy. There are two other galaxies that move along with Andromeda. Messier 32 is on the bottom side of M31 at about four o’clock. M32 is a compact elliptical galaxy and is comprised of mostly older red and yellow stars that are densely packed. Messier 110 is above M31 in this image and is a dwarf elliptical galaxy. There apparently are at least 11 other satellite galaxies of M31, but none that are apparent in my image to my knowledge.
Collecting the data
For my first attempt, I traveled to the Astronomy Site at Broemmelsiek Park in Defiance, MO. This is an excellent place that provides several concrete platforms along with electrical access for those with equipment that needs it. I did not, but I was looking for an area not too far from our home to find as dark of skies as possible. The sky at this location (Bortle class 5) is darker than where we live (Bortle class 6) and is 25 minutes away. This is a pretty good site for viewing the night sky. I was really excited when I turned my birding scope at 60X power to Jupiter and was not only able to view the banding and colors of the planet, but could also make out four of its moons! However, there was still enough light pollution here to make serious astrophotography a bit of a challenge. Unfortunately, this was more of a challenge due to where M31 was located in the first half of the night. At this time of the year M31 rises from the NE sky and it was not until ~ 11:30 pm that the galaxy rose enough out of the skyglow of civilization to make me a little more comfortable.
For this attempt I was using a Canon 5d mk iv camera and a Canon 300 mm f/2.8 is mk i lens. I balanced this heavy kit on the Sky Watcher Star Adventurer Pro Pack star tracker. Because of the weight of this kit, I used an additional counterweight and bar to achieve balance. This is near the weight limit that this star tracker was designed to hold.
The first step in going about this is to get polar alignment with the celestial north pole. I won’t go into too much detail here, but I found this to be particularly problematic. After trying for 45 minutes I eventually decided I was “close enough” but definitely not at optimal alignment. Getting as close to perfect polar alignment is critical at longer focal lengths and exposure times in order to capture the stars as pinpoints of light. A big part of my problem here was working with the mounting “wedge” that comes with this tracker. I found it quite difficult to get the precise control that is necessary to align Polaris where it needs to be. I will eventually need to replace this wedge with one of higher quality.
After getting marginal polar alignment, my next step was to mount this rig, get it balanced and then point it at the target all while not moving the tripod at all! I am sure I moved it somewhat off the alignment that I managed to get. Because of the light pollution, I was unable to see M31 with my naked eye, which is possible under dark enough skies. This made locating M31 more challenging than I expected. With the help of star charts and astronomy apps on my phone, I eventually found it by taking shorter exposures with very high ISO to be able to compose close to how I wished. This probably took another 30 minutes.
With the mount polar aligned, the target in my sights and the tracker running, I was finally able to collect my data. My settings were as follows: 20 second exposure time, f4 and ISO 1600. A little explanation here is needed. With this tracker and kit, I could theoretically get between one and two minutes per exposure. However, with the imperfect polar alignment I knew I had and the fact this was my first attempt, I decided to go with a shorter exposure. For my aperture, I gave up a full stop of light. However, I was worried about how the stars looked fully open and decided at the last minute to close to f4 to gain a little in the IQ arena. I am not sure this was the best decision or not and will probably try wide-open next time..
I collected 265 “lights” before clouds, that were completely not predicted by all of my weather apps came in and closed me down for the night. Later I cut this down to 225 lights that were unaffected by clouds or airplane lights for a total exposure time of 1.25 hours. While in the field you are supposed to take “darks” – these are frames at the exact settings under the same environmental conditions but you throw your lens cap on. These images are then used by the computer programs to remove the digital noise that is produced during capture. Somehow I forgot to do this in the field and did not remember until I was slipping into bed at 3:00 am. So, I got out of bed and went outside to take them.
Processing the data
It may seem crazy looking at this image, but I spent around 12 hours processing this. Much of this time is due to me not being very familiar with what I was doing. I also prefer to process as manually as possible, and used no specialized plug-ins in Photoshop.
Prior to Photoshop, all of the data needs to be stacked in the computer by specialized software. I first tried to use Deep Sky Stacker (DSS) that I have used for this type of work before. However, I ran into problems. After loading all my lights and calibration frames the software refused to run and gave me typical ambiguous reasons. Doing some troubleshooting online it looks as though my data weren’t good enough – apparently my stars were not round or sharp enough and I could do nothing to get DSS to process my data. I then played around with a couple of other free astro-stacking softwares. Most of these were far too technical for me to easily learn them. I finally found Sequator and this worked great. It does not accept “bias” calibration frames, but I doubt that I could recognize their absence in the final product.
I then took the stacked image and went through the “stretching” process in Photoshop. This is where you increase the local contrasts, trying to bring out details in the arms of the galaxies, nebulosities, etc. There are a number of steps involved in this last bit of processing. Much of what I did I learned from Charles Braken’s book, The Deep-Sky Imaging Primer and YouTube videos from Nebula Photos, Peter Zelinka and others.
Conclusions and what I learned
I realize this type of image is built mostly by technology. There really is not much subjectivity when making images of deep-space objects. It either looks like the thing or it doesn’t. I also realize that there are people doing this that have much more appropriate equipment and knowledge and can produce a much better version of a DSO than I could no matter how much I practice. However, I have found it very rewarding to be able to produce an image of M31 myself, especially using camera equipment I already owned and use for other things.
Here are some things I believe I have learned and can potentially help me improve in my future attempts at making DSO images. If you are an experienced DSO imager and can offer any further suggestions, I would be very much appreciative!
- Getting better polar alignment
- Getting more practice should help here and I will try and do this on nights that I am not planning on shooting, potentially from my yard.
- I have read and seen videos where people are suggesting upgrading the wedge mount and I will do this eventually.
- Collecting more data
- I believe I could pull more details from the galaxy’s disk, including colors by collecting more data. I was limited by clouds for this one, but next time I hope to get at least four hours. I know that some pool data collected from multiple nights, but that is another layer of complexity I probably do not need right now.
- Finding darker skies
- There is no doubt that skies with less light pollution will allow for better data collection at a faster rate. This will definitely help in pulling fine details and colors from DSO’s. There are light pollution filters, but I have heard mixed thoughts regarding their benefits.
- Beware of dew
- I knew this, but forgot to take the heating elements to wrap the lens barrel in order to prevent dew forming on the lens objective. Thankfully, the lens hood seemed to protect from this, but at the end of the night I did notice a thin haze of condensation on the lens.
- Learn more on processing
- There are numerous ways to skin this cat and I hope to learn more by watching more techniques on YouTube. With trial and error, I am certain that I can improve the final image by learning more here.
Other than the above, the only thing I can think of that would make a big difference is purchasing technology. People who really get into this use specialized telescopes, specially modified cameras, guided trackers run by computers, filters and much more. However, I do not intend to go down this road and believe I can produce images that will satisfy me with the equipment I already have.
If you have an interest in DSO photography and have the basic equipment, I urge you to give this a try. All you need is a camera and lens that is about 100 mm – 500 mm. A star tracker is definitely helpful but not required! You can shoot DSO’s with simply a tripod. Other than that you will need to learn just a few things on how to adjust the settings on your camera and where to point.