In my last post, I talked about my introduction into astrophotography. During the same trip, I attempted star trails – those beautiful concentric circles/arcs you see when turning your camera skyward and sucking up all possible light for minutes or even hours.
I’ve always been curious about star trails. The fact is: given the chance, your camera can see more than human eyes. This is why photos of the night sky look so surreal. There’s no way that many stars are visible from our tiny little planet.
The technique sounded fairly straightforward: set your camera on a tripod, leave the shutter open for an hour or so, and voila! neat swirls. I questioned how you’d know exactly how long to leave it open so as to get a proper exposure, but that’s what the wonderful world of the interwebs is for!
My searching revealed more than I bargained for. I didn’t realize there was more than one technique to achieve those stellar shots (pun intended). While I was familiar with the all-in-one-shot approach, I soon discovered you could also stack multiple images together – and that this often resulted in better quality shots.
I really wanted to explore this idea, so I used this blog post for research. I decided on the stacking technique. I also had this wild idea of double-dipping by doing a trail time lapse (I’ll dive into that with another post). Instead of duplicating Dan’s instructions for trails, I will simply focus on the lessons I learned through this process.
First, read what I learned from my mistakes with star photography as a whole. Most of those tips are applicable here as well.
An intervalometer is a fun accessory!
I just purchased a basic one online; I only spent around $20, though I know there are far more expensive ones out there. The most important thing to ensure is that it works with your camera.
This is such a simple tool to allow for shots at perfect intervals. Set the delay for how long you want the camera to wait before you start shooting, the length of time you’d like to keep the shutter open with each shot, and the amount of time to wait between each click. For my trails, I used 5 seconds, 60 seconds, and 1 second (most won’t let you have an interval of less than a second; you need this to allow time for the camera to write the image to your card), respectively. This device could be used for star shots (obviously) and time lapses. I would love to explore the latter really soon.
For either star trails or time lapses, this piece of equipment is essential, unless you want to spend your evening staring at your watch and hoping you press the button at just the right moment. It takes the guesswork out of the process, ensuring you get perfectly spaced images.
Do some research beforehand
I didn’t have much time prior to our excursion, so I admit I rushed it a bit. Had I read up a bit more on it, I might have adjusted my technique somewhat. I read 30-40 seconds for a shutter speed, but even these appeared a bit dark, so I worked my way up to minute exposures, and I stuck with that the entire night (sadly, also for my stills). I learned later that this is far too long. As a result, every picture wound up slightly blurry. This is excusable on the trails shots, as I intended to make a motion composite anyway, but the overall quality would have been improved with a faster shutter. And I certainly should have had a faster speed for my stills (as noted previously).
Take a few foreground shots
The idea is this: for the first few shots of your star trails, illuminate the foreground. You can then use this illuminated foreground in your final image, after you’ve stacked your stars, replacing the black silhouette. The silhouette works, too, but it’s good to have the option if you want to bring in some of the foreground details.
I didn’t think to do this while I was out there, but I happened to set up near a spot where people were walking by with headlamps (see my next point), periodically lighting my foreground, so I decided to bring some of that in. I’ll make more of a deliberate effort to do this next time.
Choose your spot wisely
If you’re alone in a field near your home or at some obscure campsite in the mountains, this shouldn’t be much of an issue. While we thought we’d be all alone at our site, we had some campmates who walked back and forth with bright headlamps, not giving much thought to what they were illuminating. Even without that, we had a lot of photographers in our group, each doing his or her own thing. Needless to say, I happened to set up too near the main thoroughfare, increasing my risk of wayward lights polluting my shots. Lesson learned: make sure your camera on its tripod will have a quiet, dark home for the duration of your shots. Any extra light introduced should be intentional.
Use a script to compile your stack post-production
Once you’ve gotten all of your shots, it’s time to pull it all together.
You can stack photos manually, but I recommend sparing your sanity by using a script. I used the script referenced in Dan’s post above, and it worked well.
For a long while, I struggled with how to actually execute it from Photoshop. All of the instructions online directed me to run a script through File -> Scripts. However, this menu item does not exist in PSE 10. On a whim, I chose to simply open it from the File -> Open dialog, and it worked. Therefore, if you, like me, are missing this option, save the script to a location you’ll remember (I saved mine in Library/Scripts on OSX Mavericks), and simply navigate to the script’s directory when you want to run it (from PSE’s Open). To have access to the .jsx file, you might need to select “All Documents” in the Open dialog, as it defaults to “All Readable Documents.” I also usually choose the Photoshop Raw format option to give me the most flexibility later. You will then be prompted to select the directory containing your photos.
Which leads me to…
Avoid opening too many RAW photos at once in Photoshop
This mistake is easily remedied, but it did cause me some headache. I tried to run the script to stack my individual images – against over 100 RAW photos. Needless to say, my poor little Macbook first took an hour or so to process so many photos and eventually display them in Photoshop, then it wouldn’t let me save the 2GB+ file. I was eventually able to save it as a PSE (a 1.4GB file that I couldn’t even open later), but I had already resolved to more-or-less start over with fewer images anyway.
Make sure the layer mode is set to “Lighten”
You should be able to watch the script run; 5 images finished within a matter of a minute or so. In your layer menu (you might need to enable the view in the Window tab), make sure the mode is set to “Lighten.” Otherwise, you will likely see just the top layer image.
This also means that your image will get brighter as you stack more layers. You’re still in no danger of overexposing a nighttime shot, but you will likely want to make a few adjustments on color and brightness once the script is done.
Find the number of images that give you the trail you like
This takes some experimentation. My first picture, made with only 5 images (I was a bit scarred after the fiasco with 100+), merely looks like I tried to take a nice nighttime shot without a tripod; the stars are a sloppy blur. Longer trails look better and more deliberate. However, you also don’t want to throw every picture into the chopper at once for one massive trail (see my point about opening too many RAW pictures in Photoshop). I personally wouldn’t try to process more than 25 raw photos at any given time.
To find the right balance, start with your maximum (25, unless you know you’d like fewer). You can then deselect layers to see the length that suits you best. Personally, I feel anything less than 10 looks like unintentional blurs. I like the longer trails, so I go for the full 25-image stack, but you might prefer something shorter.
If you really do want longer trails, you can repeat the stacking process with a few 5-image (or more) stacks that have already been saved down to 30MB so you aren’t attempting to open 2GB of images at once.
Higher-quality images highlight every glaring flaw with its precision
Fresh out of the script, I was dismayed to see holes and disjoint lines in my trails. However, as soon as I saved them to .jpg, the lower quality blurred the pixels splendidly. Therefore, don’t be discouraged until you see the finished product!
Once I had the stacked image I was happy with, it was time to bring in some foreground. By sheer happenstance, I got a few shots of illuminated foreground, courtesy of my unaware campmates. First I brought this in. Adding a new layer to the existing background is as simple as opening the foreground image, cmd+A (select all), returning to the background image, and cmd+v (paste). A new layer is automatically created; be sure to switch the mode to Lighten.
I deleted the stars in the middle from my foreground layer; I already had the trails I wanted, and I didn’t want errant stars from another image cluttering my final shot. You can use the brush selection tool for the first cut and the eraser tool for more precise edgework. This is what it looks like with the rock and tree brightened:
The contrast was a bit much, and the rock was slightly overexposed (I didn’t intentionally paint it, after all), so I used a low-opacity eraser to better blend with the original background. I also softened the foreground edges a bit. Additionally, I corrected some of the coloring, bringing out the blues and deepening the blacks.
I used a third image to bring in some of the other branch in the upper left, using the same techniques as above.
Finally, I brought the image back into Lightroom for some final tweaks. These included lens corrections, a bit more touchup on the coloring, some minor noise reduction, and a slight vignette.
When all was said and done, this is what resulted:
It was a fun experiment, but this certainly isn’t the best I could do. However, I know how to improve for next time, and I’m sure it will go smoother then. It was a great first try, and I’m excited to get back out there to try again!
If anyone has done their own star trails, I’d love to hear your own tidbits, what you learned and how you improved your own techniques. In the meantime, happy gazing!