03 - June 7, 2017: Shooting Stars (2 of 4 - Star Trails)
This is the second in a series of entries covering night sky photography for beginners. If you're just starting out, I recommend you read through part one, which covers what gear you'll need to have a successful, and enjoyable, session.
Now that we've covered what gear you'll need to successfully capture the night sky, it's time to delve into the actual technical skills and setup that will be required to put that gear to good use. The best gear in the world doesn't amount to anything if you don't know how to use it! I've broken this piece into two separate entries: Star Trails and the Milky Way. Even if your goal is to only capture the Milky Way, I still strongly encourage you to read through this page as I cover information that is useful to both capturing star trails and the Milky Way.
FIRST THINGS FIRST - WHAT NOT TO DO
Before you even start your setup, I highly recommend checking (or double checking) each of the following:
• DO NOT use a filter*: Remove any UV, polarizing, or neutral density filter you may have attached to your lens - you don't need it and it may/will screw up your shot(s)
• DO NOT use image stabilization: If your lens has image stabilization, disable it - it can cause focus drift on longer exposures
• DO NOT use in-camera noise reduction: Disable long exposure noise reduction in your camera settings, especially for star trail sessions - it will slow down your shooting and may/will create gaps in your star trails as a result (through trial and error you may find that in-camera noise reduction helps when capturing the Milky Way... it will depend on your gear and settings)
• DO NOT let your camera die: Don't start shooting with a battery that isn't fully charged - you may be taking a few hundred shots and don't want your camera to die before you finish
• DO NOT let your intervalometer die: If you're not certain that your intervalometer batteries have a decent amount of charge left, swap them out for new ones before starting - as with your camera battery, the last thing you want is for your intervalometer to run out of juice part way through
* There are some filters that can help cut through light glow from city lights but, generally speaking, no filter is better - your best solution is to go out far enough to minimize interference from such lights.
FOREGROUND ELEMENTS AND LIGHT PAINTING
Alright, one more important thing to cover before we move on to actually taking shots with your camera: light painting. As will be covered below, the composition of your shots will be extremely important and, with that, comes the importance of having interesting foreground elements in your frame. While you can certainly rely on silhouettes to add interest to your shot you will likely want to light up the foreground at some point, and that's where light painting most often comes into play. I don't want to overcomplicate this explanation as it really comes down to trial and error in the field so, ultimately, it's a "simple" matter of using a flashlight or other portable light source to "paint" objects with light. It is definitely an art more than a science as you need to balance beam width, brightness, and how long you light up objects to have a good end result.
One additional piece of advice, though: given the propensity of LED lights these days you may want to find a warmer light source. Modern flashlights all tend to lean heavily towards the pure-white spectrum and, in my opinion, that's not really what I want for light painting. I've recently ordered a warm spectrum LED flashlight and also dug out an old fashioned MAG Light that still has an actual bulb. I'm looking forward to trying them out to see if I can get a less harsh end result without introducing too much yellow into my shots.
Shooting Stars | Creating Star Trails
Hopefully, you have a camera and a lens or two that meet my recommendations covered in part one of this series. Namely, a body that can perform well in low-light conditions at higher ISO, and at least one lens that is reasonably wide-angled and fast. On my 80D, I have captured star trails using both my Sigma 17-50mm lens at an aperture of 2.8 and my Tokina 11-20mm at 2.8. That does not, however, mean you need to shoot wide open to capture trails; you will find that it may take some trial and error to find the sweet spot for your particular camera and lens as some lenses are sharpest at a step or two down from wide open. Below are the settings I used for my first attempt at capturing star trails (you'll see later that I tweaked my setup for my follow second attempt):
Overall, I was thrilled with this first effort. Frankly, I was expecting to fail miserably… but, if I'm being honest, the outcome does have its flaws (I'm also my own worst critic). The worst mistake I made was not giving myself enough time to setup my shot; I was with a large group of people and I wasn't quite ready when everyone started, resulting in my focus being off just enough to be noticeable on the foreground elements.* Thanks to my just-missed focus, the star trails came out slightly thicker than expected, too. I don't actually mind that as it really makes the trails stand out but, in the end, I learned the hard way that the most important step of shooting the night sky is the setup for your composition.
* Your group size is another important factor; I recommend no more than 5-7 people, max, to make it easier to coordinate everything.
Having learned my lesson about the importance of setup at Fort Griffin, I gave myself plenty of time to stage my composition and get everything right before starting the session (it was also a much smaller group, with only 5 of us to coordinate). At the time, I thought the thicker star trails from my first attempt were due to using f/2.8 for the aperture - rookie mistake - so I decided to shoot at f/5.0. I've since realized that the issue was my focus being off as opposed to shooting wide open. Thankfully, the narrower aperture didn't ruin the outcome… which leads to another point: you don't need the fastest lens in the world to capture star trails. While a larger aperture will certainly help it is not as critical here as it is for capturing the Milky Way. You likely won't capture as many trails as fainter stars won't be picked up but you will still have success at capturing a nice star trail shot.
SUCCESSFULLY COMPOSING YOUR SHOT
Although I've only shot the night sky a handful of times, each time I've done so with other people I've always heard the following question: "How do I compose my shot when I can't see anything?!" The answer is to crank up your ISO as far as it will go and shoot as much as you need until you are certain you have the composition you want, and until you can really dial in the focus. These shots won't be pretty but they will help make your initial composition much easier.
Aperture: Wide Open
Shutter Speed: 10-15 seconds*
* Or as long as necessary to get a bright enough image to check your composition and focus
Top Left: Leveling the horizon at Lake Tahoe
Top Right: Not quite bright enough at The Rock Church
Bottom Left: Lining up the North Star at Mt. Rose Hwy above Lake Tahoe
Bottom Right: Composing the shot to avoid interference from passing traffic
At the above settings, your shot will come out extremely grainy and probably won't impress you much BUT it will allow you to see your foreground elements so you can make sure you're level, have the composition you want for the foreground, and can focus appropriately. That last point - focus - will be easier or harder depending on your lens. With my Sigma 17-50mm I have to focus all the way out to infinity and then still have to do some fine tuning to really dial things in (as I learned at Fort Griffin). With the Tokina 11-20mm it's as easy as setting it to infinity every time (note that this is where your headlamp comes in handy; you'll want to see the infinity marking on your lens, if it has it). On a recent outing overlooking Lake Tahoe, my sister and niece came along and we quickly discovered that the 18-135mm Canon kit lens that my sister brought doesn't have any markings for focus, and it doesn't even have a hard stop for the focus ring, which meant it took quite a few setup shots to finally get the focus dialed in. It was still possible but it was definitely much more difficult and time consuming (I was ultimately able to use my flashlight to light up a tree in the foreground of her shot just enough for her to focus on it while zoomed in using Live View).
Beyond the importance of the basics - level, and in focus - you also have two other extremely important factors to consider:
1) Find an interesting foreground element; I mention it above for a reason! It's the foreground that will make your image stand out from others, and it will allow you to create a shot that is unique (not to mention there's no point in traveling to different locations if all you do is capture shots with nothing but stars). Even if you are with a group, seek out different angles, heights, objects, etc. from everyone else. It's not very fun to compare results after the fact and have an image that looks like everyone else's. An interesting and unique foreground is what makes for an interesting and unique night sky shot!
2) If you have multiple options for your foreground, you also need to consider what type of star trail image you want to create. Do you want the classic ring of circles expanding outward across the night sky? Then you are going to have to find the North Star (Sirius) and have it in your frame. If you want to create a feeling of the stars leaping across your frame, you don't need Sirius in-frame. Or you can mess with viewers' perceptions and have opposing arches of star trails by composing your shot to include "reflecting" trails with the celestial equator dividing the night sky into two parts. All of these provide an opportunity for you to create something beautiful and unique - have fun with it!
Lastly, make sure your tripod is well planted. You don't want it to shift at all during the session; if it's windy out, you may want to leverage some weight bags or your camera bag - if you have a center hook on your tripod - to help provide some added security.
Once you have your composition set and everything is locked in, you're ready to go!
INTERVALOMETER VS. SINGLE EXPOSURE
You have a choice to make at this point: You can either shoot one extremely long exposure to generate star trails, and more or less be done with it, or you can shoot multiple shorter exposures which you will later stack together to generate star trails. While the first option is technically simpler, it is also - in my opinion - far riskier. What happens if an unexpected light blows out your shot? What if someone or something interferes with your foreground? You have no way to recover from that if you're doing a single, very long exposure, and you'll have wasted a good chunk of time (what if the issue happens at the end of a 90 minute exposure?).
I personally can't see myself ever not using an intervalometer and image stacking to generate my star trail shots. Yes, you have to have another piece of gear (the intervalometer, unless your camera has a built-in one that will meet your needs) and, yes, you have to spend more time on the computer stacking all the images together and blending layers to get the perfect foreground shot, but you also eliminate the risks I just outlined above. You eliminate the worry of having your entire session ruined by a single, careless mistake. You could have 50 frames of a 300 frame capture with ruined foreground elements but, as long as your sky is fine, you can easily recover from that in post-processing (which will be covered in Part 3). Even if the sky isn't recoverable in some shots, the worst you'll have are small gaps in your trails, as opposed to a completely lost effort.
I'm assuming you will follow this recommendation - after four night sky outings I am clearly an expert, after all (/sarcasm) - and, therefore, you'll need to understand how to use that intervalometer thing.
UNDERSTANDING THE INTERVALOMETER
Although an intervalometer can be used as a simple remote shutter release, it offers far more functionality, which makes it exactly what is needed to capture multiple exposures for star trails. You do need to understand what the various values mean, though, before you can properly prepare for your session.
DELAY: This value determines the delay between pressing the shutter and taking the photo and, for our purposes, won't be used.
LONG: This value determines how long your shutter will remain open.
INTERVAL: This value dictates how long the "pause" between each shot will last.
N VALUE: This value allows you to choose how many total exposures you want to capture.
TIMER START/STOP: Fairly straight-forward; start and pause/stop your captures.
SHUTTER BUTTON: When your camera is in Bulb mode,* press for a single shot; how long you hold it down will determine the length of the exposure. Most intervalometers also have an exposure lock feature that lets you lock the shutter button in place, saving you the hassle of holding it down constantly on longer exposures (if you aren't using the intervalometer itself to control that).
LOCK: A single press will turn on the backlight (on this model, at least) while holding it down will lock the device so nothing can be inadvertently changed.
* Different camera models and brands may have different ways of selecting Bulb mode. If you're not terribly familiar with your camera model, I urge you to read the manual ahead of time (and bring it with you, if your memory isn't the greatest!). For instance, on my Canon T5i it was a matter of turning my shutter speed dial to select 30 seconds and then turning once more to enter Bulb mode. On my 80D, Bulb mode is an actual separate selection option on my Mode dial.
Now that you (hopefully) understand what each intervalometer setting does for you, you're ready to move on to setting each value appropriately for your star trails session.
Long: 00:00':30" (30 seconds)
Interval: 00:00':01" (1 second)
N Value: 240*
* You have some flexibility on this setting. My first session at Fort Griffin was done with 240 images while my second at The Rock Church was upped to 300. I've also gone as low as ~85 captures; it completely depends on what you want out of the image. If you're composed to have the North Star in your shot with circular trails rotating around it, you'll want to use a higher number to have fuller circles. If the North Star isn't in your view, you may want to use a lower number to simply get enough shots to have lights streaks from each star. Or, you may use a lower number if you're freezing your butt off and just really want to get somewhere warm sooner than later (been there, done that)!
So, you've set your composition. You've dialed in your focus. Your intervalometer is set and ready to do its job. All you have to do at this point is hit the Start/Stop button on the intervalometer and kick back and relax. If you're with a group of people, this is a great opportunity to sit around and talk, maybe enjoy a drink or two, and just have a good time. Me being me, I usually check on my camera every 15-20 minutes if I'm not sitting right by it; I've had two experiences with a stranger or strangers showing up mid-session and there's always paranoia associated with an unknown person being around your gear - and your person - in the middle of the night. On the flip side, when a random guy showed up towards the end of our star trails session at Lake Tahoe and set up a tripod I was comfortable getting out of the car and striking up a conversation while he set up for his own Milky Way shots. You should, of course, keep safety in mind at all times, and having a group of people with you helps minimize risk.
Once your camera stops firing away, or you opt to manually end your session, you're just about done with the star trails shoot! The last step you want to take is to capture a "dark frame" shot by using your lens cap. This allows you to capture a frame that will help filter out sensor noise when stacking the images together. By capturing this dark frame at the end of your session you'll do so while the sensor is at operating temperature; higher sensor temps beget higher sensor noise. When you include a dark frame in your image stacking process that noise will be automatically removed, saving you some time in cleaning up the end result in post. More on that in the final Shooting Stars entry!
Whether your goal is capture star trails, the Milky Way, or both, your starting point is the same provided you have the appropriate gear: focus on your composition to create interest and a unique image. Plan ahead, scout locations online or through local photography groups, and leverage technology (such as the PhotoPills app) to help you coordinate your setup and timing as needed.