Capturing the Earth and sky in one great composition is surprisingly easy.
By Babak A. Tafreshi in the Sky & Telescope November 2012 issue
Seen from a little island off the coast of Brazil, the Milky Way hangs above coconut palms. Gentle waves break the island silence, softly washing the shore’s tiny grains of sand. Millions of those grains are under my feet as I stand next to my camera, trying to capture both the boundless cosmic ocean above and the quiet terrestrial one below.
This attempt to capture the beauty of the Earth and sky is known as landscape astrophotography. The resulting nightscapes made using off-the-shelf cameras and lenses are immensely successful in astronomy outreach. Picturesque terrestrial landmarks crowned with the stars above allow viewers to relate to otherwise abstract celestial sights. These wide-field photos often reveal surprising astronomical and atmospheric phenomena impossible to record through a telescope’s narrow field of view. We often think of the universe as an astronomer’s laboratory, but these celestial portraits remind us that the night sky is also an essential part of nature — and therefore of us.
Striking this balance between art and science in nightscapes is one of the more challenging aspects of landscape astrophotography, but if done properly, these images can revitalize the sublime experience of naked-eye observing.
Get started in astrophotography with our FREE Astrophotography Primer, a guide to shooting nightscapes, the planets, and far beyond.
Right Place, Right Time
Today’s nightscape astrophotographers are pursuing the hobby at the right time. When I began photographing the night sky in the early 1990s, photography was a complex and fickle endeavor. My first successful sky image came after months of trial and error with a single-lens reflex camera. I had to figure out the best films and exposures, as well as find a reliable photo lab. Today, thanks to digital technology, delicate Earth and sky images appear on my camera’s LCD screen as soon as the exposure is complete.
Compared with telescopic astrophotography, nightscape imaging is a low-gear endeavor; you don’t need a vast array of high-tech equipment. A single camera, tripod, and a shutter-release cable will not only get you started, they are almost all you need as a nightscape astrophotographer. Post-processing of your images is also minimal, because you’re aiming to create an image resembling what an observer might see with the unaided eye.
Keeping your equipment as compact as possible also helps you tackle the real challenge of landscape astrophotography — getting to the right location at the right time. Much of your setup time will involve traveling to remote locations, searching for picturesque landscapes, and waiting for the right moment. Unless you’re particularly fortunate, you’ll never take the best nightscapes in your backyard. The view down your street with electricity wires, streetlights, and other signs of urban life will often degrade an otherwise wonderful nightscape. Being at the right place at the right time usually comes with careful planning, which includes knowledge of the night sky.
Having the minimal amount of equipment not only helps you move around during the night to find the best compositions, it also allows you to enjoy your time under the starry sky. My usual imaging gear consists of two cameras: one used to capture still images that I move to different positions throughout the night, and another to record time-lapse sequences. Everything fits conveniently inside a backpack.
Also consider the size of your team. I tend to avoid doing night photo sessions when I’m alone, and I always let someone know where I’m going when I shoot from a remote location. On the other hand, larger groups cause their own issues, including too many tripods to trip over and sometimes too many flashlights in my photos. Astrophotography in small teams of two or three people is often the most comfortable
Choosing Your Gear
The most important tool for taking world-class nightscapes is obviously your camera. Although some great twilight photos can be taken with pocket digital cameras, serious landscape astrophotography is impractical with compact digital cameras. Their average nighttime sensitivity is mediocre at best. The newest point-and-shoot cameras use small detectors boasting a dozen megapixels or more, which may sound wonderful at first. But these detectors incorporate extremely small pixels that aren’t well suited for nightscapes, as I’ll explain in a moment. Additionally, compact point-and-shoot cameras come with a single zoom lens, which more often than not is both photographically slow and often has poor edge quality that reveals itself as distorted stars near the corners of the image.
The best choice for nightscape photography is a digital single-lens-reflex camera (DSLR). These cameras feature dozens of advantages over point-and-shoot cameras, including high sensitivity, interchangeable lenses, manual exposure and aperture settings, bulb exposure mode (which enables practically unlimited exposure lengths), and a RAW file mode that preserves the dynamic range of your image (June issue, page 68). Most recent DSLR models utilize “live view,” which provides on-screen focusing and can display the brightest stars at night, greatly simplifying the process of achieving proper focus.
DSLRs are very sensitive to light, much more so than even the best films of the past. And while you can adjust the ISO setting to achieve “faster” performance than point-and-shoot cameras, the latest models offer much lower noise at the same ISO settings than cameras manufactured just a few years ago. Changing the ISO setting of your camera doesn’t truly increase its sensitivity to light, but rather electronically amplifies the signal readout from your camera’s CMOS detector. This amplification has the cost of producing more noise in the image.
A DSLR’s true sensitivity depends on a number of factors, such as the sensor’s quantum efficiency, or QE. This is the percentage of usefully recorded photons compared to the total that strikes the detector. The QE of a human eye ranges from 1 to 5%. A rough estimate for the peak QE of current DSLR cameras ranges from 30 to 40%. Note that the QE changes across the spectrum and thus depends on the wavelength of the light striking the detector. A camera’s QE also varies in each of the RGB color filters incorporated in the camera’s Bayer matrix.
Under a dark, moonless sky, current DSLRs perform well at ISO 1600. This is a good compromise between photographic speed and noise in the resulting images. A goal in nightscape astrophotography is to capture a sharp landscape and pinpoint stars. You can often avoid tracking if you limit your exposure to roughly 30 seconds with a 15-millimeter lens, or up to a minute with very wide-angle or fisheye lenses. Beyond that, the stars will trail noticeably. Some new camera mounts, such as Vixen’s Polarie (reviewed in the March issue, page 58), compromise between the stars and foreground image by tracking at half the normal rate. This speed allows you to shoot longer exposures before stars become objectionably long trails while also not contributing much blur to the foreground.
Slower ISOs of 200 to 800 work well at twilight, in bright moonlight, or in considerable light pollution, and when shooting star trails. Slower ISOs record fewer stars and won’t capture fainter objects such as the Milky Way in short exposures of the sky, but they have the benefit of lower noise, better dynamic range, and they produce more saturated star colors.
The Multi-Megapixel Lure
Another important factor that determines a camera’s sensitivity is the size of the individual pixels in the camera’s sensor. These tiny, photon-collecting wells are like buckets collecting raindrops. The larger a pixel is, the more photons it can collect before it gets full, or saturated. Although new cameras that boast small pixels provide higher resolution and capture sharper details (particularly in telescopic planetary imaging), they lack the sensitivity of sensors with larger pixels, and the small pixels quickly saturate during long exposures. Rapid saturation results in colorless white stars across the field and low dynamic range when using high ISOs.
Another consideration when choosing a camera for nightscape astrophotography is determining if you want a full-frame sensor or one of the smaller APS-format cameras. A full-frame sensor requires lenses that can illuminate the whole detector. This is an important consideration, because most camera manufacturers offer lenses specifically for their APS cameras, and these will seriously vignette the corners of the full-frame camera.
While some of the best choices for nightscape photography are full-frame cameras such as the Canon 5D Mark II and the Nikon D3, they aren’t absolutely necessary. Under a dark sky and using a good wide-angle lens, you can make a 30-second exposure at ISO 1600 on most current APS-format cameras and still record a surprisingly glorious view of the Milky Way. When choosing an APS-format DSLR for nighttime imaging, remember to avoid budget models with high megapixel counts, because their super-sharp daytime performance won’t last when the Sun sets.
Lenses as Your Telescopes
Even the best DSLR cameras produce mediocre images when coupled with a cheap lens. Consider investing in high-quality lenses with fixed focal lengths. Zoom lenses are often inadequate for any kind of low-light photography. The wide-range zoom lenses such as the standard 18-to-200-mm zoom that comes with many camera packages offer you both wide views of constellations and close-up Moon shots. But these complex lenses use many optical elements and offer slow photographic f/ratios that limit how deep you can go in short, untracked exposures.
The basic lens for nightscape photography is a wide-angle lens ranging from roughly 15 to 35 mm for full-frame cameras, ideally f/2.8 or faster. An APS-format camera lens equivalent would range from 10 to 24 mm. These fast, fixed-focal-length lenses are the key to success in low-light photography. With a fast 15-mm f/2.8 lens, a 30-second exposure at ISO 1600 will reveal faint nebulae and star clusters within the Milky Way.
When shooting with lenses faster than f/2.8, stop the aperture down one or two f/stops to achieve the sharpest focus and to reduce coma at the corners. For example, a good 24-mm f/1.4 lens should be stopped down to at least f/2 to produce good star images across the entire image.
For close-up views of celestial events such as conjunctions or eclipses, a telephoto lens in the range of 85 to 200 mm is required. Longer, fast telephoto lenses (500 mm and more) are quite expensive, and small apochromatic refractors with similar focal lengths are usually much better optically and less costly.
Shooting Old School
Finally, what about film cameras? Film nightscape astrophotography is still alive (see images by The World at Night photographer Oshin Zakarian at www.twanight.org/zakarian). Film cameras are very affordable and still a perfect supplement to your digital equipment. Available films today are relatively slow but work fine for imaging at twilight, under bright moonlight, and for long-exposure startrails. Film cameras with manual shutters don’t require electricity to function in bulb mode. Medium-format film cameras are available on the used market often at bargain prices and produce wonderful nightscape photographs. You can still find medium-format films of ISO 800 in many professional photo stores, or online.
These tips should get you well on your way to capturing wonderful scenes of conjunctions, meteor showers, and the resplendent Milky Way above the most beautiful locations in the world. Nightscape astrophotography is among the easiest and most enjoyable pursuits for amateurs today, and is by far the most accessible to everyone.
S&T contributing photographer Babak A. Tafreshi is the founder of TWAN (www.twanight.org) and is the 2009 co-recipient of the Lennart Nilsson Award for scientific photography. See more of his nightscapes at www.dreamview.net.