|Camera:||Canon EOS 5D Mark III|
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With pretty much any DSLR, a sturdy tripod, fast lens, and just little knowledge, you can now capture landscapes beneath more stars than you ever imagined possible. A camera’s ability to accumulate light allows it to reveal stars far fainter than the naked eye sees; rapidly advancing digital SLR technology now enables usable (low noise) images at the extreme ISOs necessary for star freezing shutter speeds in very low light.
I’m starting with the assumption that you have a relatively new digital SLR, one that allows you to capture fairly clean (low noise) images at 1600 ISO or higher. You’ll need to be fairly comfortable with managing the controls in the dark, and know how to get it into manual and bulb modes. For star trails a locking remote release is essential (one that allows you to lock down the shutter rather than forcing you to hold it down for the duration of the exposure).
And of course don’t even think about trying any of this without a rock-solid tripod (you don’t need to spend tons of money, but neither can you assume any tripod will work—it won’t!). A wide (35 mm or wider on full frame is best), fast (at least f4, but the faster the better) lens is best. Oh yeah, and take off your polarizer.
Getting the exposure
Moonlight photography is great for photographing landscapes beneath a few bright stars, but a sky filled with stars (and maybe even the Milky Way) can only happen when there’s no moon and city light to wash out the faint stars. When I go out on a moonless night, whether my goal is pinpoint stars, star trails (or both), I start with a test exposure to determine the amount of light my planned image requires. The test exposure also allows me to check my focus, level, and composition in light that’s nearly opaque to my eyes.
My initial test exposure is usually no more than one minute at an extreme ISO (the goal isn’t a usable image, it’s solely to determine the exposure) and my lens’s widest aperture. After each click I check my LCD, adjust, and reshoot. The first frame is mostly to gauge the light; subsequent frames refine both the exposure and composition. I’m usually ready to go after two or three test frames.
Once I have an exposure that works (the ideal combination of stars and foreground light), I just need to decide which shutter speed will give me the star effect I want—short for pinpoint stars, long for star trails. With that, finding the ISO and/or f-stop that adds or subtracts the light subtracted or added by my chosen shutter speed is just simple math.
For example, let’s say my test exposure was perfect at ISO 12,800, f2.8, and 15 seconds. A thirty-two minute star trail image will gather a lot more light (than my 15 second test exposure), so I start by figuring out how many stops 30 minutes adds to 15 seconds. Since I have to double ¼ minute (15 seconds) seven times to get to 32 minutes, I know going from 15 seconds to 32 minutes adds 7 stops of light. (2×1/4=1/2 minute -> 2×1/2=1 -> 2×1=2 -> 2×2=4 -> 2×4=8 -> 2×8=16 -> 2×16=32.)
On a moonless night there’s not enough light to see the controls on your camera, the contents of your bag, and the tripod leg you’re about to kick. Needless to say, there’s not enough light to focus either, at least in the traditional ways.
Because we’re usually wide, and very rarely including close detail, our night subjects are almost always at infinity. Unfortunately, that old prime lens habit of twisting the focus ring to the end for infinity focus doesn’t work on a zoom lens—every time you change your focal length, you need to refocus. While I’ve simplified my night photography by going almost exclusively with a 28 mm f2 prime lens, in those rare times I do use a zoom, I usually use it at its widest focal length. Not only does a wide lens maximize the amount of sky in my frame, the extra depth of field increases my range of focus tolerance. And sticking with a single focal length reduces the times I need to hassle with focus.
Despite the hardships, there are a number of methods for focusing at infinity in the dark. Here they are in my order of preference:
- 1. Autofocus on a bright planet or star. Some camera/lens combinations have excellent autofocus (the faster the lens, the better). I always start by picking out the brightest planet/star. Venus is great, but it won’t be up during the darkest hours of the night. Jupiter, Saturn, and Mars can work, as can Sirius and maybe a few other stars. Regardless, you don’t need to know what you’re pointing at—find something bright in the sky, center it in your viewfinder, and try to focus. (Any bright, distant object will do—headlights, a plane overhead, whatever.) Don’t forget to take your lens out of autofocus as soon as it’s focused.
- 2. Live-view focus on a bright planet or star. With my camera on my tripod I center the brightest object in the sky in my viewfinder and lock it in place. I go into live-view mode, center the star/planet in the LV magnification square, then magnify the view to the maximum (it’s 10x on my Canon), and manually focus. Don’t forget to take your lens out of autofocus as soon as it’s focused.
- 3. Autofocus on a nearby flashlight. When all else fails, I have somebody stand 50 feet or so away with a flashlight and autofocus on that. If I’m by myself, I rest the flashlight on a rock (or whatever) and walk (stumble?, grope?) 50 feet away. Believe it or not, if I focus my 28 mm f2 lens (for example), on a point 50 feet away, I’ll be sharp from about 25 feet to infinity, so you should be fine too unless your lens is significantly longer (which I don’t recommend for night photography) or faster (lucky you). Don’t forget to take your lens out of autofocus as soon as it’s focused.
Don’t forget!: Because there’s no fixed infinity on a zoom lens, if you change your focal length, you must refocus.
Because I love stars, and it’s the stars that really set a night image apart, most of my night images are at least 80% sky. The foreground is more of a placeholder, an excuse to dazzle you with the celestial ceiling. But that does not mean the foreground doesn’t matter. Quite the contrary, because the sky is a relative constant, the foreground is the difference between another pretty picture and something that pulls people from across the room.
It’s not necessary, but when possible I always try to include something recognizable, such as the Big Dipper, Orion, or the Milky Way. This is especially nice in pinpoint star images. If you don’t know the night sky, spend a little familiarizing yourself with the major constellations—you can find many, many smartphone apps to help with this.
Most people’s vision subconsciously runs along the long edge of an image. Since the primary feature or a night image is the sky, at least 2/3 of my night images are oriented vertically. Probably more than 2/3 are vertical when my foreground is simply an anchor for the sky, and slightly less when the foreground has enough power to compete with the sky. Regardless of my orientation bias for a particular night shoot, I always make sure I have at least one vertical and horizontally oriented image.
I’m constantly on the lookout for a striking foreground to feature beneath a starry sky. Bold objects without a lot of intricate detail work well. Reflective subjects, like water, granite, and sand, work well too. When all else fails, find a rock or tree to silhouette against the sky.
In Yosemite I like Half Dome for the way it stands out against the sky. The Grand Canyon is one of the few locations a magnificent expanse that can match a dark night sky, but it’s also just a dark hole without lots of light—I’ve had better luck with Grand Canyon my star trail images because the long shutter time allows enough light at a very clean ISO. My current favorite location for night photography is the Kilauea Caldera on Hawaii’s Big Island, which has the added advantage of its own light source and surrounding terrain that can stay black (allowing pinpoint star shots with an ISO still low enough to be manageable).
Successful star photography is all about managing star motion—either minimizing their motion or maximizing it. Unfortunately there’s an inverse relationship between the number of stars you capture and your ability to freeze their motion. In other words, for any given ISO and f-stop, the longer your shutter is open, the more stars you’ll expose, but the more they’ll move during your exposure.
Pinpoint star images require (relatively) fast shutter speeds to freeze the stars’ motion; star trail images require long shutter speeds, the longer the better, to maximize star motion. (Of course it’s not the stars’ motion we’re capturing, it’s Earth’s rotation against a fixed backdrop of stars, but you already knew that.)
Some nights I shoot both pinpoint stars and star trails; other nights I only photograph pinpoint stars. Because a pinpoint star image is usually only 15 to 30 seconds, even after I’ve completed my test exposures they’re the best way to make sure I have everything right before moving on to the quite lengthy star trail exposures.
I’ve seen a formula floating around that’s supposed to ensure pinpoint stars. It’s called the “Rule of 600” and goes something like, “Divide 600 by your focal length to ensure a shutter speed that will freeze the stars.” My concern with solutions like this is that they sound far more precise than they are, and they create a false sense of security, often leading to longer or shorter exposures than necessary.
The problem is, the amount of motion is a function of (among other things) a star’s distance from the axis of rotation. For example the North Star, which is less than a degree from Earth’s north axis, will show very little motion in exposures of many minutes or even hours; Betelgeuse, on the other hand, because it’s near the celestial equator will show a significant amount of motion in just a few minutes. For pinpoint stars I think it’s more important to find an exposure that delivers enough light with the least amount of noise. So go ahead an use the Rule of 600 as a starting point, but don’t assume it’s Gospel.
What do I do? For pinpoint stars I shoot with a wide lens (28 mm or wider on a full frame) and keep my exposures under 30 seconds—motion has never been a problem for me (you can make your own determination of what is and isn’t acceptable). I know I can get usable images that clean up nicely with noise reduction software (Topaz DeNoise is my choice) at 3200 ISO. If I’m pointing north (less star motion) I’m more inclined to expose for 30 seconds if it’ll buy me a lower ISO; pointing more toward the celestial equator (east or west), my bias is usually toward a higher ISO to allow for a faster shutter speed. But the exposure is the priority, so I don’t hesitate to go all the way to ISO 3200 for 30 seconds if the light calls for it.
Many people are having great success photographing star trails by combining many consecutive, relatively short exposures. In general this approach reduces noise and results in a cleaner image. But since all my images are captured in a single frame (I’m a film shooter with a digital camera), you’ll need to look elsewhere for that method.
My star trail images are usually 20 or 30 minute exposures, which I find to be more than adequate to achieve the effect I’m looking for. Start with pinpoint stars and stick with those shots until you’re happy with your composition, exposure, and focus. When you’re ready for star trails, without changing your composition, focal length, or focus (you’re on a tripod and I’m assuming you’re happy with your point star results):
- Turn on your camera’s long exposure noise reduction (most cameras have it, though it’s usually buried deep in the menu system). LENR isn’t necessary for pinpoint stars (though it may help slightly), but it makes a noticeable difference in star trail images. The downside of LENR is that it doubles your exposure time (it basically takes a second exposure of the same duration with the shutter closed, compares the results, and subtracts whatever it finds in both images). That means if you take a 30 minute exposure, you’ll need to wait another 30 minutes before viewing your results.
- Put your camera in Bulb mode. On some cameras Bulb mode is one of the choices on the Aperture Priority, Shutter Priority, Manual (and so on) dial; on others Bulb is the next step after 30 seconds in the Manual shutter speed.
- Now it’s time to do your exposure math. Assuming you want the same exposure (amount of light) you have in the pinpoint star images, determine how many stops of light your star trail shutter speed will add, then subtract that amount of light with some combination of lower ISO and smaller aperture (larger f-stop number). For example, if your star trail exposure is 30 seconds at ISO 3200 and f2.8, a 30 minute exposure would add 6 stops (technically a full 6 stops would be all the way to 32 minutes, but those extra two minutes are inconsequential).
- Now you’re ready to shoot. If your camera allows you to block the light entering through the viewfinder, now’s the time to engage that (if you don’t know what I’m talking about, you probably can’t do it, so don’t worry about it). Click the shutter button on your remote, lock it down, and check your watch or set a timer.
- Enjoy the view.
I’ll soon be adding a couple of paragraphs with my thoughts on processing night images, so keep checking here.