City Star Trails: A Comprehensive Guide to Star Trails in Light Pollution
Introduction to Star Trails and Pre-Shoot Thoughts
To shoot star trails, generally, dark skies and a crescent moon are needed for the stars to be visible. Even in dark skies, a full moon can overpower the light of the stars. The widest lens is used to capture as many stars as possible and the lowest aperture of that lens is set to allow in as much light as possible. Infinity focus is set or, if you don’t have infinity focus, you’ll employ the LCD method. Interval shooting is used and stacking in post is employed to give the stars their trail effect. More on dark sky star trails will be available in another blog post. Now that you know the basics of star trail shooting, let’s move on to city star trails.
When you hear the phrase star trails in the city, you often think of one of two things. Either, a sky so blown out that no stars are even visible or a hazy sky (due to light pollution) where the trails seem unimpressive. If the light of the full moon can overpower the light of the stars, how would the stars even be able to compete against a fully lit city skyline?
.1 Notice how even above the city, there is still an area of haze that cancels out a ton of the stars. Only the brightest stars can be seen and even then, they're dim and few in number Flickr
.2 This shot is a bit better but the stars still are dim and the sky still seems hazy. Cite
Walking in Boston, I remember seeing stars in the sky and if there’s one thing I know about night time photography, it’s that if you can see something at night, the camera is able to see it better. I was very skeptical about the widely accepted belief of the impossibility of shooting city star trails. During the night of the blood moon, I remember taking a shot of the sky and seeing a plethora of stars. I truly believed that it would be possible to pull off such a shot and I wanted to produce something that would wow even the most veteran of photographers. After discussing with some hobbyist friends and some photographers in the in industry, none of them believed it was possible. However, I was so hell-bent on producing this shot because I had this gut feeling that it could be done.
.3 Look at the PLETHORA of stars in Boston
Brainstorming
I knew this was going to be an incredibly difficult and advanced shot. If I pulled this off, it would be a monumental feat. For the best shot, I needed to pick
A scenic location (preferably a skyline)
Have either a half, crescent moon, or new moon
Clear skies with 0% cloud cover
A location with minimal light pollution
I eventually settled on the Cambridge side of the Charles River. Looking at the Boston skyline, the location should be far away enough that light pollution wouldn’t be a problem for most of the stars in the sky. The next issue would be weather. Thankfully, using the weather underground app, I found a night where cloud cover was 0% for 9 hours and the moon was a waxing crescent. (If you’ve never used weather underground, I highly recommend you start. It’s one of the most accurate weather apps I’ve ever used and can provide you with basic weather information as well as detailed information such as hourly temperature fluctuations and precipitation conveyed in the form of a line graph. In addition, Weather Underground has a feature called Smart Forecasts which tell you the most optimal times for any outdoor activity. From, landscape photography to running to star gazing to wild flower photography, Weather Underground has you covered. It also displays sunrise and sunset times as well as the phase of the moon that night. Weather Underground is currently my main weather app and I’m not even sponsored by them.) Before I could commit myself, I needed to know that the stars would be visible. During one of my golden hour shoots, I decided to stay past twilight and test my hypothesis. While it wasn’t the prettiest shot in the world, it did prove that this concept could be possible.
.4 stars in the city. They are definitely visible
As you can see, in a 30-minute period, I was able to get some star trails. The foreground was blown out so doing some local adjustments, I was able to properly expose it. But, it’s not the cleanest shot. I knew that the final shot would have to have a composite. One of the stacked stars and one with a properly exposed foreground.
Shooting
To shoot this kind of shot, you’ll need a few things:
Tripod
Wide angle lens (optimal but you can use any lens you want)
Remote
Batteries on Batteries (in 5 hours I went through 3) or your own set up for extended power
Tripod counterweight
DSLR (obviously)
Patience…. A LOT of PATIENCE
It’s gameday. Time to do something that so many people thought was impossible. The cloud cover is 0% and golden hour is ending. I had just scouted for 40 minutes to pick the most optimal composition of the skyline. I tried to find a frame with an interesting foreground element and employed the rule of thirds. In the case of this shot, the boat makes an interesting foreground element. I set up my camera, remote, tripod, and tripod counterweight. The tripod counterweight and remote are important. You don’t want any camera shake and even the smallest shake from the wind or your shutter finger can ruin the shot.
Knowing that I needed to make a composite to compensate for the blown highlights in the foreground when I stacked my test, at around 7:30pm, I started with a blue hour RAW shot at the lowest iso as a base composite for my stacked star trails. I employed focus stacking (which I’ll talk about in another blog post) to get everything in sharp detail in the frame. After waiting an hour, the first stars started showing up. Using the PhotopPills app, I calculated the longest exposure time I would need for the most accurate stars. I ended up at ISO 800 f3.5 10s at 10mm. At this point, you want to switch to jpg to reduce the amount of space the photos take up on the SD card. Also, it will make stacking easier on your CPU in post and the jpg format won’t matter because we’re going to blend the stacked frames into our focus stacked RAW file. So, set your settings, shoot in jpg, and shoot at around 4k white balance to really illuminate the stars. Now to focusing on the stars.
Because my lens doesn’t have infinity focus, I had to use my LCD screen and the manual focus ring to get the stars as sharp as I could. To do this, you start in live mode. Using the screen and the focus ring, get the brightest star that you see on the LCD as small as possible. Take a few test shots at a high iso to make sure that the star is in focus. Make sure that once you set the focus, you remain in MF. Time to start shooting.
I used a technique called interval shooting, which is just a fancy way of shooting multiple shots of the same frame to stack later. Make sure IMAGE STABLIZATION is OFF. Once I had my focus set and my composition ready, I set my camera to continuous mode and started shooting. This is when your remote comes in. Make sure that you have your remote and the shutter on the remote is locked. This way, you don’t have to constantly press the shutter button. The camera will now automatically continue to take photos. Now you play the waiting game. I waited from 8:30pm to 1:30am at the same spot and ended up with 2212 star frames and 3 blue hour shots for stacking. Don’t be discouraged if you don’t see anything in your frames. I think this is where most people give up. The initial single shots will seem hazy with only a few stars. This will all be remedied in the stacking process. If you can see 1-2 stars in your frame, you’ll be ok. At some point, you will run out of battery. There are products you can buy to extend your battery’s life. Or, you can make your own setup out of a dummy battery and an external power bank (in another blog post). If you don’t have either, you must make sure, MAKE SURE that when you change, you change quickly, and move the camera as minimally as possible or not at all. Change fast to eliminate gaps in the stars and don’t move the camera or stacking in post is going to suck. Practice a ton of times before shoot day. You don’t want to spend hours in a spot and have your shot messed up because you moved the camera when changing the battery.
.5 One of my shots for stacking. As you can see, there aren't that many visible stars. The process will fix that. Have faith. I used the star in the top right to focus.
Post- Processing
For my post processing, I used a few different programs
Photoshop
Lightroom
Starstax
Windows Photo Viewer
To start, I took all 2212 frames into Starstax, a free software for star trails, to see if it was at all possible. This was the big turning point. If this worked, then this style of shot would be possible. After stacking, this is what my initial photo looked like.
. 6 As you can see, Starstax has illuminated all the stars in the sky. Even with all the stars you see in the frame, there are still more stars in the shadows that you can illumiante if you up the exposure.
As you can see, the stars are illuminated in the night sky. Also, the foreground gets really blown out. Starstax stacks exposures on top of each other. This means that the more frames you take, the brighter the final image highlights will be. Therefore, you can see the stars in the city. With 2212 exposures stacked on top of each other, the night sky stars will get bright. The only problem is all the air traffic in the sky.
After I finished stacking, I decided to do the composite and make sure that everything could be stitched together. Again, the blue hour composite is shot to help properly expose for the foreground.
.7 Composite of blue hour and star trails
In Photoshop, I took the stacked shot and used the blend mode lighten to blend the stacked layer onto the blue hour focus stacked layer. Not all the stars are as visible as the previous shot and all the air traffic is still present. This is ok. We will fix that later. The important thing is that the composite works.
Now comes the most tedious part of the post processing process: cleaning out ALL the air traffic. To be honest, at this point, I didn’t really know what to do. None of my friends would’ve known. They didn’t even think this was possible. So, like every normal 20-year-old, I turned to Google and found this article. Feel free to give it a read. While our shooting processes are quite similar, we differ in the post proccessing. I think the concept of a star trail in the city is still very new in the community as this was the only detailed article written on the subject.
To take away all the air traffic, it’s simple. All you must do is open your windows photo viewer (or whatever it is on the Mac) and take a black brush and paint out every plane trail in every frame. Sometimes, the trails are hard to notice so make sure that you are extra attentive in this step. If you miss a few after you’re done, a mask and brush in Photoshop will fix any small mistakes you’ve made. This step will take the most time. Just focus on the opportunity and the end goal. This step took me about 20 hours in total.
After you’ve tediously brushed away all the plane trails, it’s time to stack all the frames into Starstax and watch as all the black brush strokes magically disappear.
.8 Stacked image with minimal air traffic. There are still a few planes in the bottom right, but I’ll brush these out later.
Using Starstax and their gap filling mode (to erase gaps in star trails) you get this clean stacked shot without any air traffic. All the black brushing that you did has magically disappeared. My guess is because with the way Starstax stacks, it stacks layer on layer, but only reveals anything with bright highlights (by using a mask and employing a threshold) on the new layer. Therefore, by hiding the plane trails and unwanted bright highlights with a dark brush, the trails get stacked over when the next image is stacked. As a reult, the sky can stay dark while the stars are revealed. This is just my hypothesis and not actually confirmed but I think it makes a lot of sense. In this frame, the stars aren’t as visible, but you can see some of the outlines (meaning you can totally brighten them later.) Go ahead and save the finished frame to your computer.
To make the composite, export the blue hour focus stacked raw file as a jpg in the highest quality possible. Open Photoshop, go to File > Scripts > Load Files into Stack… Select your blue hour shot and stacked star shot and open them as layers. Make sure that auto align in the prompt box is checked. If you forget, just shift click and select both layers, then Edit > Auto- Align Layers… This will align your layers together making brushing easier. Crop away any blank space. Next, arrange the star stax layer on top and the blue hour layer on bottom. Set the blend mode of the star layer to lighten. Create a layer mask on the Starstax layer and, to the best of your ability, brush away the foreground of your shot without brushing away the stars in the frame. If you want, use the pen tool to make a selection of the foreground so you can brush it away. At this stage, you may find that the color of your stacked shot differs from your blue hour foreground. Open another file window of your blue hour shot by going to File > Open… and find your blue hour shot. Next, in the window of your composite, go to Image > Adjustments > Match Color… and play around with the luminance and color intensity until the colors match. Congratulations! You’ve successfully made a star trail composite using the stars at your location!
9 Finished Composite
Now, some of the stars may not seem very bright. This is easily remedied with luminosity masks ( A blog post will be posted in the future on how I use these techniques) Congratulations! You’ve done the impossible.
.10 Final image with stars brightened and my post processing applied
Conclusion and Final Thoughts
The process for this shot is pretty complicated. The most important things to remember:
Make sure your weather conditions are perfect. If you can’t get a day with 0% cloud cover, you must make sure that the moon is new or in a crescent phase.
Get the blue hour shot in. It’s impossible to have both the stars exposed and the city exposed properly. You must composite it. (There might be a way to do it without the composite but at this moment, I haven’t figured it out. The outcome of compositing vs not compositing would be the same either way because you’re using the stars on location.)
Make sure your camera is STILL. You don’t want to try to auto align 2000 frames and export them out in Photoshop. Your computer will not be able to handle that even if they are in jpg format. Employ your bag as a counterweight to guarantee your tripod won’ t fall over.
Once you get the shots, you can mess up as many times in post as you want until you get that perfect shot. To recap post processing
Load all jpg star files into StarStax and start with the lighten blend to see how many stars you can see
Composite in the blue hour shot to make sure the concept works.
Use a black brush in your default photo app and go frame by frame in your star shots with a black brush to paint out any plane trails
Load the cleaned images into StarStax with a gap filling blend mode to fill any gaps in the trails (the second the shutter closes before your camera takes another shot in continuous mode)
Composite that shot into the blue hour shot and use masks and brushes (or pen) to paint away the foreground
Use the match color option to match the color of your foreground to your stacked shot or vice versa
Follow normal post- processing workflow.
For this one shot, you will invest a lot of time. You might give up half way through the shoot but you must have faith that the finished shot will be fine. I wanted to bail so many times during the shoot, but I pushed myself to stay and it was completely worth it. Do not attempt this shot if you are relatively new to post – processing or photography in general. The techniques used are quite advanced to get the desired outcome. Learn the basics and then come back to this guide. Go ahead and wow your friends
Commentary on this shot:
“Shoot for the Stars”
As with all my shots, I always want a foreground, mid ground transition, and background. Scouting, I found this beautiful composition with 2 boats. The water was also calm, so the reflection was almost a mirror image. In the final image, I deleted one of the boats and had only one boat in the center of the frame. I think one subject in the foreground is infinitely more powerful than 2 boats especially when looking at the night sky. The one subject in the middle of the frame helps to convey the loneliness and isolation against the vast night sky, even if the scene is in the city. There’s something to be said about the contrast of one (especially one placed in the center) vs many. For the background, I did a little crop so the Prudential and 1 Dalton could be in the middle of the shot. The reflections and the water act as a great transitioning midground and the reflections act like leading lines from the boat to the skyline as well as introduce more colors.
Click Here to download my Shoot for the Stars Timelapse and Wallpapers for phone, tablet, and computer!