If you want to escape the sunset crowds at Clingman’s Dome, come back at midnight. The beauty of night photography is that there are no crowds. The downside is that you have to do it at night!
Perhaps the most interesting aspect of the night sky is the Milky Way, at least from a landscape photographer’s standpoint. But where to find it? A little astronomy knowledge helps here. Our galaxy is a huge disk composed of billions of stars. Our solar system sits about half way between the center of our galaxy and it’s outer fringes. As the earth spins, the Milky Way rises in the East, passes overhead, and sets in the West, just like the sun, the moon, and all of the stars.
Consideration of the time of year, time of day, and phase of the moon are important for capturing the Milky Way. In the late winter and early spring, the Milky Way can be seen rising in the East at about 4:00 AM. At this time one can capture the entire arc of the Milky Way in one exposure or a short panorama. The most interesting part of it, the galactic core, is always at its southern end. Each month it rises about 2 hours earlier, so that by mid-summer it is visible just after twilight. The earlier rising occurred during the day so it was not visible. By about 10:00 PM in the summer, the Milky Way can be seen rising in the South and passing directly overhead with the galactic core just above the southern horizon. In late summer and early fall, the Milky Way rises from the Southwest and arcs in a westerly direction.
Figure 1. The arc of the Milky Way rising in the East. Picture taken from the Blue Ridge Parkway at 4:00 AM in late April. The Galactic Core is at the southern end.
From November to February, the orientation of the earth is such that the galactic core is not visible, but the bulk of the Milky Way is still visible—the orientation of the earth is such that we are looking at the outer fringe of our galaxy rather than at its center.
Clouds and moonlight interfere with photographing the Milky Way. One can’t do much about the former, but it is possible to work around the moon. Night skies are quite dark 3 or 4 days before and after a new moon. A little light from a crescent moon may actually help lighten the foreground of a night scene. Even when there is a full moon, it may rise after or set before prime Milky Way viewing time.
Figure 2. By mid-summer, the Milky Way has passed directly overhead by the time it is visible after twilight. In this picture, taken in mid-July at 10 PM, the Milky Way rises straight upward from the Southwest.
Unless one is interested in close-ups of individual star clusters, the foreground is important in Milky Way photos. Scouting potential shooting locations with a compass during daylight is highly recommended. The wide dynamic range of the night landscape means that the best exposure of the sky will leave the foreground as a silhouette, as in Figure 2. Alternatively, one can take a second exposure optimized for the foreground and blend the two in Photoshop as in Figure 3.
Figure 3. The Milky Way above a rock formation in Rocky Mountain National Park. Separate exposures for the sky and the rocks were blended in Photoshop.
Having found the Milky Way, ideally from a location well away from city lights, the challenge is to photograph it. This requires a modern DSLR, ideally but not necessarily full-frame model, manual focusing, a fairly fast wide-angle lens, and a sturdy tripod. The goal is to capture as much light in as short exposure time as possible. Several factors enter here: the Earth is spinning! Therefore, at longer exposures the stars will become dashes instead of dots. The longer the focal length of the lens, the more the apparent motion of the stars is magnified. The oft-quoted 500 rule states that dividing 500 by the focal length of the lens gives the longest exposure that can be used without star streaking. Thus, for a 50mm lens, 10 seconds would be the longest usable exposure. In practice, I find this much too generous. With my 35mm lens, 10 seconds is the maximal exposure time to preserve star sharpness, more like a 350 rule.
Figure 4. Cropped image of stars taken with a 35mm, f/1.4 lens with 15 second exposure, the maximum recommended by the 500 rule. The stars have become dashes instead of dots, probably not noticeable on a Facebook posting but very apparent on a large print.
Although articles on the internet recommend use of an extremely wide angle lens, such as a 14mm, f/2.8, it is important to remember that the amount of light captured is proportional to the lens’ physical diameter. Thus, at a given f-stop, a 35 mm lens captures much more light than a 14 or 20 mm lens. My current lens of choice for night photography is the Sigma Art 35 mm f/1.4. The angle of view is not as wide as a 14 or 20mm lens, but more light is captured, allowing use of a lower ISO setting. A series of exposures can be stitched together with software such as PTGui or Photoshop if a broader landscape is desired.
Focusing in the dark is challenging. The camera’s autofocus will not work. Nothing is more frustrating than expending a lot of time and energy on a night photo excursion only to discover the next day that the pictures are all out of focus. (Trust me on this). The depth of field is very shallow at fast f-stops such as 1.4 or 2.8. There are several methods available to focus the lens at night, such as focusing at infinity during daylight and taping the lens at that point, or placing a small flashlight in the distance and focusing on it. The most precise method is to use the Live View feature of the camera, magnify the image while aiming at a bright star, and carefully adjust the focus while viewing the LCD with a small magnifying glass. You will be surprised at the sensitivity of a fast, wide-open lens to minor adjustments of the focus ring. If a zoom lens is used, it may need to be refocused each time the focal length is changed.
Night photography images typically require considerable post-processing. The images right out of the camera often look quite bland, but if shot in RAW, contain rich color data. There are numerous tutorials on the internet suggesting ways to process Milky Way images, some unfortunately aimed more at producing pretty pictures than making an accurate depiction of the night sky. Because a modern digital camera captures much more color than can be seen by the human eye, there is no simple “gold standard” by which to judge whether the colors are correctly displayed. Many tutorials suggest shooting at cooler white balance, such as 3800-4000 Kelvin, use of very high ISO such as 6400 or higher, and enhancing the highlights to make the stars brighter. The image in Figure 2 illustrates this technique. However, the night sky is seldom blue and the stars are a variety of colors, especially blue, orange, and red. Bands of red and green, often seen just above the horizon, are airglow produced by oxygen and hydroxyl atoms that have been excited by ultraviolet light during the day.
Figure 5. The Milky Way in Rocky National Park. Airglow produces the bands of green and red seen just above the horizon on the right side of the image.
My personal preference is to shoot in RAW at daylight white balance and an ISO of 1600 or 3200, use Lightroom to correct for lens distortion, chromatic aberration, and noise, increase contrast with curves, increase saturation slightly, and do final editing in Photoshop. The night sky is often a fascinating combination of greens, reds, and oranges and I try to preserve these colors. The bright star just to the right of the Milky Way, Antares, is reddish-orange, so it serves as a guide as to whether color rendering is accurate.
Figure 6. Out of focus image of stars to illustrate the many colors present in the night sky.
The internet is loaded with articles and videos about photographing the Milky Way and processing the images. Two sites to start with are that of Kevin Adams and that of Roger Clark. Kevin’s website, especially the Digital After Dark blog, contains a wealth of information about night photography, and if you’re on his email list you get a monthly reminder of the astronomical events of the coming month. Roger Clark’s website is an exhaustive repository of images and articles about all aspects of digital photography with numerous articles regarding night photography. His perspective is informative because he comes from a background as an astronomer, rather than as a former landscape photographer who suddenly discovered his DSLR worked at night.
The author, Howard Gutgesell, is a retired pediatric cardiologist who divides his time between Virginia (Spring and Fall) and Colorado (Summer and Winter) with periodical excursions into the Smoky Mountains, Shenandoah National Park, and Rocky Mountain National Park. More Milky Way images can be seen in the Shot in the Dark gallery of his website www.HPGphotographics.com. Kevin Adams is responsible for creating his obsession with night photography.