Anatomy of an Image - Mackinac Bridge and Comet NEOWISE
Astro photos are quite polarizing. You are attempting to record a scene in which your eye cannot, or barely can, see. As a result, a vast majority of these types of shots do require multiple exposures, tracking, stacking, and blending to bring out the hidden details. This is especially true when shooting into light pollution or with deepscape subjects. I wanted to preface the article this way because if you are uncomfortable with blending shots to create a final composition, then Astrophotography may not be for you. This DOES NOT mean they are not real scenes. They absolutely are. We are working with the limitations of the gear to create the highest quality image possible.
July proved to be a month to redeem the rest of the year's rather insane chain of events. A comet became visible to the entire northern hemisphere. Comet NEOWISE would go on beyond just a beautiful binocular object. This celestial visitor was clearly visible to the naked eye. Dazzling the world over! Soon the entire Astrophotography and Nightscaper community pulled their collective camera together to record this comet from all over the world. A wonderful reminder about how celestial events can help us heal. I digress, though.
"DeepScapes" and Telephoto Lens Compression
The moment I first heard about the comet, I sprung into action to find memorable landmarks to photograph with it. I also realized that this would be a fantastic opportunity to plan a few deepscape images around. A great in-depth article on DeepScapes:
Deepscapes are similar to the "big moon" photos. It creates this compressed field of view exaggerating the main subject with a secondary one. The resulting effect is one that suspends reality and really brings those heavenly objects close to home. I REALLY wanted one with the comet!
What causes this rather jarring, yet captivating, effect? A few things. I cover this a bit in a previous article on photographing the Moon. To recap, I'll pull into this article what I wrote in the Moon one. The first phenomena is an optical illusion known as the Ebbinghaus illusion.
How does it work? Two circles of identical size are placed near to each other, and large circles surround one while small circles surround the other. This juxtaposition creates the illusion that the central circle surrounded by large circles appears smaller than the central circle surrounded by small circles. Yet, they are the same size.
Beyond the illusion, there are several studies out there as to why we perceive a Moon - and other objects - on the horizon as so much larger than when above the horizon. Some theories stem from binocular vision, or that as your target subject rises, we lose that reference to a terrestrial object, and thus have nothing to compare it to anymore. If you would like to read more on this phenomena, check out this study: https://www.pnas.org/content/97/1/500
The second aspect is a concept known as "Lens Compression". A more correct term for this would be "Focal Length Compression". As it really has nothing to do with the lens per-se. Lens compression is a type is distortion. This phenomenon makes background elements appear much larger and closer than they actually are. This distortion gets more pronounced as the focal length increases. While the use of lens compression is popular for portraits, it can be shocking when applied to landscapes. Mostly because landscapes are shot wide angle. Think about that for a second. When was the last time you shot a landscape over - say - 50mm? Flip from a 14mm to a 200mm, and the scene is going to look very different!
As I watched the comet photos flood the internet, I noted most were shot with the typical wide angle lenses. People got used to seeing a "small" comet. There were a number of telephoto shots posted, as well, but not with landscapes incorporated. Without the frame of reference, this doesn't look out of the ordinary. However, couple that telephoto comet shot with a landscape, and holy cow, what a view! The comet literally fills the entire frame. This is the effect DeepScapes go for.
The above time-blended composite image of the Mackinac Bridge was shot with a 35mm lens. This is the field of view most people are accustomed to. Note the comet's relative size.
More on lens compression can be found here: https://www.slrlounge.com/lens-compression/
Challenges of Astrophotography with Long Lenses
Utilizing the longer lenses at night does introduce a few new problems. The biggest of which is how quick star trailing happens. Once you creep towards 200mm, this will happen in a second or less. You almost always will need to use a star tracker of some sort. The exception is if you want to do star trail shots, of course! Using a tracker means that you can no longer shoot single exposures if you have any sort of landscape foreground.
This is where the photography community will fight like cats and dogs over what's a composite image and what isn't. Generally speaking, if you don't move your tripod and shoot the exact same scene from the same night, these are blends, and not composites. Yes, I am aware of the actual definition of a composite. However, in this case, you are working with the limitations of the gear. You are NOT taking elements from a different location, day, scene, or Google image search and adding it into your final composition. THAT is a composite. I strive for an accurate representation of the scene as it was. These are blended shots. Otherwise, why would i stay up all night waiting for that perfect alignment?
Next up focus and camera shake. Telephoto lens are harder to nail focus with at night. Some of this is contributed to the fact that when zoomed in, any slight touch or breeze introduces shake. This is important to remember overall. Once you start hitting focal lengths of 600mm, you'll find yourself having to use mirror-lockup on the DLSRS, to help alleviate the camera shake. Be sure to have a good, preferably wireless, remote to trigger the shutter. The less actual touching of the camera the better!
Finally is framing your scene. During the day this is less apparent since you can see everything. Heck, I've never paid attention to how little you have to move a telephoto shot to make a big difference in the scene's framing. At night, it'll smack you in the face. You do not need to move the camera much at all to completely change the framing! This is why people that shoot DSO have those nifty Go-To mounts! Trying to find an object millions of miles away in a sea of stars at 200+mm is next to impossible. Ha!
Also, depending on the weight of the gear, a counter weight may be needed. With the Nikon Z6 and Nikkor 70-200mm, I haven't needed one. If you cannot get a clean shot with pinpoint stars, and your polar alignment is good, look to the weight balance.
The Sky Live
Shots like these require much more careful planning, since you are dealing with a small field of view. Then add in the ever-changing position of a comet, and it becomes even more challenging. Luckily, there are tools available online and though phone apps to help pre-visualize your shot.
Several planetarium programs are available at your fingertips. Stellarium is extremely popular, and available on desktop and mobile devices. However, I kept hearing mixed messages regarding adding the new comet to the program. Some said it was free, other said it was a paid premium. I ended up using this online planetarium to plan a few shots. It's free, easy to use, and best of all - web based. How accurate is it? Enough to allow me to get the shot I was after!
This is where I went AWOL from all the media outlets. Most of the media articles on Comet NEOWISE stated that it was only visible for a few hours after sunset after July 15th (It was a dawn object prior). HOWEVER, if you live or were in a northern latitude - say 44 degrees north or above - NEOWISE was visible ALL NIGHT. Starting around July 12th, I was able to see the comet skim the horizon before moving back up in Wisconsin's Door County. As the nights progressed,the comet would continue to stay higher and higher above the horizon.
Another misconception portrayed by the media was the direction of both the tail and for viewing. Due to the fact they stated it was only visible a few hours after sunset. During that window of time, NEOWISE was in the Northwestern sky. As the night progressed, the comet move to the North before moving Northeast as the sun rose. That brings me back to the plan at hand.
The Mackinac Bridge faces a North/South direction depending on what side you are on. I wanted the comet framed by the towers, which faced north from Mackinaw City. Well, according to the planetarium app, on July 20th around 3:12am, it would squarely be facing north. One must also take into consideration the altitude. Didn't want it to far below the bridge, or to high. There really was only a handful of days where this alignment was the best.
Now that we know where Comet NEOWISE was going to be, we need to figure out if the rest of the scene will work. Enter PlanIT! Pro. This fantastic tool lets you pre-visualize a shot with astonishing accuracy. PlanIt! features constellation overlays, which is invaluable. Star charts and constellations helped locate the comet. NEOWISE liked to hang out in the Big Dipper. Which is nice because that is a very easy constellation to find. Even bortle 9 zones can see the Big Dipper.
The first step is to load your location in. You can do this by a search feature, or just pinning the GPS-based dot. From here, move the field of view (in green) to where you hope to shoot. Changing the focal length will also effect your field of view. I usually kept it around 50mm, as it was easier to spot targets. Then I changed to to the desired focal length to fine tune.
To further visualize the shot, you can bring up the Virtual Reality mode. With the constellations on, this helps you pinpoint where your subject will be in relation to the horizon and if its even in your view! The compass below along the bottom will help orient yourself in the direction of shooting. The app also will load elevation maps, so you can see if there's a mountain in your way. I was in Michigan, so very little mountains to worry about! Ha!
Alright! The time as come! You have waited up all night for this moment. The moment where - the comet in this case - graced your frame! This is the most critical part of your imaging session. As you want your main subject to be as close to the plan as possible. I fired off six 1.5 min tracked shots as the comet moved across the bridge's towers. Seeing the faint icy snowball show up on the back of the camera was nothing short of amazing! Even though the light of the bridge, there it was, tail and all! I then shot the untracked foreground shot. Which I always shoot more than one, just in case. This night was quite windy, so I had several unusable images due to camera shake. You can shoot foreground prior to tracking, too. Completely up to you.
In the above image, you can clearly see the comet and its tail - even through the heavy light pollution! The position, direction, and size are true to the final image. Note how much the foreground moves in a 1-minute tracked telephoto shot. Here in lies the problem and why single image shots with a foreground are not possible.
Once you are happy with your tracked shots, concentrate on the foreground. Or if you already captured the foreground, you're done! I make it a habit to go back and check focus on the images, and for any issues with camera shake and the like.
I chose a foreground shot after the tracked ones to use. Notice how much the comet moved in that short amount of time. This was maybe a half hour worth of shooting.
The Magic of Stacking - Even with Tracked Shots
It is completely feesable to use the two above shots to create a final blended shot. However, if you are anything like me and want the max amount of detail from these kinds of lighting conditions, you'll want to stack those tracked shots in a program like Deep Sky Stacker. These programs were developed for - you guessed it - deep sky imaging. All those beautiful and pretty photos of nebulae and galaxies benefit from many images stacked together. The more data you have, the more the computer can extract! Lately a few of us have been combining the art of deep sky imaging with landscape elements to create these otherworldly compositions.
In the cropped image above, you can easily see the detail from the tail! Six tracked images netted a huge gain in data through the lights! Pretty amazing, right? No need to slap in a comet from somewhere else!
Putting it All Together
Here is where the magic happens! Initial adjustments, such as white balance and exposure, are done in Lightroom or Camera RAW. Matching the color casts and exposure between the shots will make your life easier. Trust me! Once satisfied, save out the individual files. The actual number of files depend on situation. For example, if you needed to focus stack, you'll have more to deal with.
Open the files in Photoshop. You can either open them all individually, or use Photoshop's "Load Files into Stack" script. The latter saves you some time of copy and pasting them over to the main master file. Nine time out of ten the next step will be aligning the layers. Believe it or not, the camera does move ever so slightly - even when taking same the same shot over and over. There are a few ways to deal with this, too. Manually, with the transform tool, or the "Align layers" script. (EDIT > AUTO-ALIGN LAYERS)
Once aligned, mask in the tracked sky shot to the foreground. All you do is add a mask the sky layer and then mask out the unwanted blurry foreground. Voila! You have created an image representative to the scene, but with much more detail, less noise, and better overall quality. Now, further adjustments may be needed, such as matching the brightness of the layers, or fixing a slightly different color cast. Also depending on how complex the foreground is, you may need to spend a crazy amount of time masking trees. Ask me how I know!
As Astrophography becomes more accessible to everyone, pushing the envelope of what's possible follows suit. What started out as single image exposures turned into blue hour blends, stacking, and focus stacking at night. Then tracking and experimenting with long lenses. Now many use software developed for astronomy for wide-field milky way landscapes. The results are spectacular, in my honest opinion! Hope you find some inspiration here to experiment with longer lenses!
Feel free to contact me with questions. I'll try my best to answer them. I hope this helps you understand the sheer amount of work that goes into these types of shots. So next time someone cries foul on a shot that done differently than the others, please ask the photographer before blasting them! We put so much time an effort in this to be dismissed as "fake" and "photoshopped". Sure we use Photoshop to edit and put it together. That is ENTIRELY different than snagging an image off Google and incorporating it. Happy shooting!