Night Photography: After the Sun Sets
The summer Milky Way on the prairie; 45 seconds, ISO 800
The sun has dropped below the horizon and the last colors of dusk have faded from the sky. You could call it a day; pack it in and go grab that meal that your stomach has been grumbling about for the last couple hours. You could…but then you would miss out on the fascinating world of night photography. In describing his discovery of the night sky on the prairie, poet Walt Whitman wrote:
The supper is over, the fire on the ground burns low,
Whitman’s discovery of the “not-day” parallels my own. Once you see the Milky Way spanning from horizon to horizon, you can’t get enough. Chance upon the Andromeda spiral galaxy and you’ll never look at the night sky quite the same. There are always new treasures to unearth, and the constant challenge to preserve fantastically dim beauty in a photograph. Over the last two years I’ve experimented with night photography and learned a lot in the process. Whether you are interested in capturing a landscape painted in the pale light of the full moon, depicting the stars wheeling overhead, or attempting to pull out details invisible to the naked eye, this article will get you started.
Before You Go
A little planning will go a long way toward putting you in the right place at the right time. My first step is to look up the basics: time of sunset/sunrise, moonset/moonrise, and the phase of the moon. Fortunately this information is readily available from the U.S. Naval Observatory website (http://aa.usno.navy.mil/data/docs/RS_OneDay.php) and many handheld GPS units. Armed with these facts, you’ll be able to plan what is possible. When the moon approaches its full phase, it will mask dim objects with its glow, but you’ll have unique opportunities to use moonlight to light the landscape. When a new moon approaches, it’s time to begin working on star trails or capturing the Milky Way.
The full moon lights the landscape in Myakka River State Park, 4 minutes, ISO 200
The next stage in my planning is to select a site for my night photography. My tool of choice is a Google Earth overlay of estimated North American light pollution. On any computer with the free version of Google Earth installed (http://earth.google.com/), simply open the kmz file available at this link: http://www.umich.edu/~lowbrows/guide/google/269838-ArtificialNightSkyBrightnessforNorthAmerica.kmz. The map uses color to indicate the severity of light pollution. These colors range from transparent for pitch black skies, up through blue, green, yellow, orange, red, and finally white in the most severely impacted urban areas. Using this map as a guide, you can place yourself in the best spot for the type of photography that you choose to pursue.
Map of light pollution for the lower 48 states, Mexico, and Caribbean
Keep in mind that extremely dark skies (green or darker) will be useful for dim objects such as the Milky Way. However, even the most light-polluted urban neighborhood holds night photography possibilities using the full moon. On a personal level, I’m saddened by the light pollution that hides the stars from my view, but by thinking creatively it is possible to turn a negative into a positive. Several times I have used the yellow/orange glow of city lights to my advantage as a way to add color to an otherwise monotone sky.
Light pollution from Twenty-nine Palms, CA (top) and Sarasota, FL (bottom) add a bit of color to the sky
Sometimes I use planetarium software to preview the night sky and how it will change through time for a site I may visit. A very capable piece of software named Stellarium is available for free download (http://www.stellarium.org/). This software makes it easy to get a quick idea of where key elements will be in your image, including the moon, planets, stars, and the Milky Way. When you first begin, you may find that this stage of planning provides information overload. If this happens to you, just go outside and work with what you find. It is worthwhile, though, to keep Stellarium in mind as a powerful tool that can help answer questions such as where the moon will rise and what portion of the Milky Way will be visible.
Finally, as the date of my shoot approaches, I want the very best information on weather conditions. I have found that a website for astronomers called Clear Sky Chart (http://www.cleardarksky.com/csk/) is particularly powerful. In conjunction with the Canadian Meteorological Center, it provides some surprisingly accurate maps of hourly cloud cover (and atmospheric transparency, humidity, wind, etc.) for more than 3,500 locations. Simply click on the state or province of your choice and browse for a location near your site of interest. The chart can appear complex at first glance, but it’s just a 48 hour forecast coded visually through a series of colored squares. Clicking on any square will pull up the full forecast map for that particular hour.
In the Field
No more planning. Now you are out in the field with the stars shining overhead. It’s time to get down to the business of night photography. I consider a sturdy tripod, camera remote release, and a headlamp to be essential gear.
How long should you expose a night photo? There really is no easy answer as there are many variables including the type of photograph you are pursuing, equipment capabilities, focal length, aperture, light pollution, moon influence, etc. My best advice is to experiment with exposures from 30 second to 30 minutes or more and take advantage of the instant feedback you will have on the camera’s LCD. While experimenting, do keep in mind that the night sky is not static. As a consequence of the earth spinning on its axis, the night sky rotates above your camera at a fairly rapid pace. Even in wide angle photographs stars will begin to streak after 30-45 seconds. If you seek to minimize streaking, your exposures will be generally be under a minute and you’ll likely need to use a fast lens and high ISO. On the other hand, if you want to showcase the star paths overhead, you’ll probably find that exposures greater than 10 minutes will have the most impact.
To attempt exposures longer than 30 seconds, you’ll want to switch your camera to bulb mode. This is usually accomplished by selecting the “B” or “bulb” shutter speed in full manual mode. In bulb mode the shutter will remain open for as long as the shutter button is depressed. You can avoid the need to directly press the shutter button by using a remote release. In a pinch when caught without a remote release, I’ve done bulb exposures the hard way, by carefully holding down the camera’s shutter button for several minutes. Your finger might cramp, but at least you’ll get some photographs!
A helpful video on bulb mode can be found at http://www.ehow.com/video_2369640_canon-eos-40d-bulb-exposures.html. This video provides instruction for a specific camera model, but the concept is similar for all models.
Hint of dawn and the moon in Everglades National Park, 30 seconds, ISO 800
The next thing that I do with my camera is switch to manual focus. Setting the proper focus distance will require some trial and error until you develop a familiarity with your lens. Usually the infinity setting goes too far and will result in out of focus stars and foreground objects. When using a new lens I usually focus closer than infinity in steps and take test photographs. On the LCD it is useful to use maximum magnification to determine when your stars are sharp points (or thin lines on longer exposures). If your lens has markings, try to note the focus setting you use in order to save time on future trips. If there are extremely bright celestial objects in the sky (Moon, Venus, etc.) your camera might actually be able to acquire focus. After autofocusing, return to manual focus and preserve that focus setting throughout the night. I’d also recommend that you occasionally check your focus settings to ensure that nothing has been bumped. Few things are more frustrating than returning to your computer after a long night and discovering that your best photographs are out of focus!
It certainly depends upon the capabilities of your camera, but you’ll probably work most frequently with an ISO setting between ISO 400 and 1600. The ISO that I choose is usually dictated by my subject. When working with the full moon I’m often able to stay quite low and use ISO 400 (sometimes even ISO 200). However, if my goal is to capture dim stars or galaxies, the ISO must be cranked up to 800 or more. Thankfully each new camera generation moves us ahead and allows the use of higher ISO’s with lower noise.
Beyond the night sky; Fireflies in Great Smoky Mountains National Park; 2 minutes, ISO 1600
Many night photographers also enjoy painting their subjects with artificial light to add additional emphasis. You can accomplish this in a variety of ways, from shining a flashlight over a scene to using the test mode on your external flash to pop in a bit of light. Pay attention to the color temperature of the light source that you use or you could get unexpected results. In general, LEDs provide an extremely cool (very blue) light that may hurt the final image. I usually prefer the warm light of my Maglite, or even my flash unit. The use of filter slips on your light allows for some very creative possibilities. At $0.01 for a pack of several dozen, you just have to add this to your next B&H order (http://www.bhphotovideo.com/c/product/45184-REG/Rosco_950SBCNG0103_Cinegel_Swatchbook.html)
Joshua Tree lit by walking through the scene and popping my flash; 2 minutes, ISO 200
Walking with a flashlight, Dry Tortugas National Park; 2 minutes, ISO 640
Many cameras now offer special in-camera noise reduction settings that double the exposure length. This feature operates by taking a second exposure equal in length to the original, but without exposing the sensor to light. The resulting dark frame roughly represents the hot pixels and noise present in the original image. It is then possible to subtract this information from the original and greatly improve image quality. I usually turn this feature off and choose to do it manually in Photoshop. For example, if you experimented with several 60 second exposures during a night shoot, end your session by placing the lens cap on your lens and taking a single image at 60 seconds. In Photoshop you can simply add this dark frame as a layer on top of your night photograph, and switch its blend mode to Difference to apply the effect. The choice is yours, but I greatly prefer to end my night with a few dark frames of varying exposure length rather than waiting for the camera to automatically apply dark frame subtraction to each and every image. Sometimes the time savings in the field can be very significant.
Long exposures greater than 10 minutes are certainly possible with many digital cameras, but sometimes you risk amp glow along image edges or a battery dying before the exposure completes. Recently, I tried a new technique for taking multiple, shorter exposures and stacking them in Photoshop. With a timer release, it was easy to tell the camera to take consecutive 1 minute exposures. After the 75th exposure I stopped the process. Fortunately, it is also easy to combine these files in Photoshop thanks to a free action from Chris Schur (http://www.schursastrophotography.com/software/photoshop/startrails.html). The stacked image can be seen below. It is worth noting that I also applied a single dark frame subtraction on top of the stack. In future experiments, I hope to tweak my settings to find an optimal balance between exposure length and noise.
Joshua Tree under the spinning sky; 75 minutes via 1 minute stacked exposures, ISO 800
As you’ve seen, photography does not need to end when the sun sets. In fact, the night can provide unique opportunities for even the most familiar locations. For me, it has become an addicting pursuit. Next time you see me yawning during the day…you’ll know why.