Having trouble sleeping? Flash not working? Grab that camera and join us for a session of night sky photography in the great outdoors. The operative words here are "night sky" and "great outdoors", as in dark sky sites away from urban lighting during the period from about 75 minutes after sunset to 75 minutes before sunrise. Here are a couple examples: the first was made on my first try at night skies on a hot and windy July night in our nearby Anza-Borrego desert. A 95-ish degree temperature and winds gusting to 25 or 30 MPH made for some fairly crummy conditions and after over 90 shots the novelty was wearing off. I was in the middle of another exposure when a bright meteor appeared in the general area of sky my camera was pointed at. The wait for the shutter to close seemed like hours but when it did, I was hooked -- the combination of a landscape illuminated by a 40% full moon and that bright smear of light has kept me coming back ever since.
The second shot demonstrates that while the moon usually plays a role in lighting the terrestrial portions of this style of night images, you can get interesting shots during periods of no moon as well. This image was taken toward the west end of Anza-Borrego facing north around midnight during the December 2012 Geminid meteor shower -- the "sunrise" is actually the lights of desert communities in the Palm Springs area illuminating storm clouds that were moving out of the area.
As you can see, we're talking about single images with exposures lasting 15 to 20 seconds on average and incorporating terrestrial features along with a portion of starry sky -- with the sky being the main subject. These aren't the dramatic deep-space shots made with expensive equipment that guides the camera/telescope for long periods of time or the product of incorporating multiple images into a single shot via computer. That being said, there are some pieces of equipment that will make the task easier.
First, your camera/lens combination needs to be capable of manual focus, or autofocus that can be established at infinity and then switched to manual or disabled. I'll explain the need for this later. If you're thinking this sounds like a DSLR, you're right, but many of the high performance mirrorless models offer feature sets compatible with night sky work -- and higher performance compacts may as well. Examine your individual equipment to see what you have available, but suffice it to say if you're shooting a compact point and shoot you probably don't have the hardware to pull this off.
Other camera considerations are good high ISO performance and the ability to trip the shutter by cable release, remote control or self-timer. A RAW shooting capability is a definite advantage but not an absolute requirement, as is a mirror lock up feature on a DSLR. Because of the long exposure times involved your camera needs to offer shutter speeds at least extending out to the 15 or 20 second range, and a "bulb" setting for longer exposures is nice to have. Fast wide angles lenses of 24mm or wider (in 35mm equivalents) lend themselves particularly well to this shooting style; longer lenses may also be used, subject to performance characteristics discussed below.
My usual setup for night sky work is a Nikon D3s (a full frame DSLR) and 14-24/f2.8 zoom lens. With the exception of our sun, stars are so distant that they appear only as points of light and through trial and error I've found that a 24mm focal length and 20 second exposure are about the longest lens/shutter combination that captures the stars as points (or nearly so) in spite of the earth's rotation during the exposure. Going longer on either shutter or focal length tends to produce star trails (elongated star images) -- which can be a nice effect in some cases. Less than full frame sensor cameras work against you in the wide angle arena due to their crop factor, but this disadvantage can be mitigated somewhat by shorter exposure times and higher ISO settings (assuming noise performance remains acceptable). If you like the star trail look a cropped sensor camera is a plus.
A tripod or other form of solid support for the camera is a must -- this style of photography does not allow for hand-holding and all the stabilized lenses in the world won't let you hand hold successfully. My personal preference is a tripod with ball head as it allows me to quickly compose shots, but you can brace and position the camera with beanbags or other such items if conditions allow. Here's a look at my setup; the "L" bracket on the camera body allows quick changes from landscape to portrait format.
I would suggest you avoid tripods with a center column or don't extend it if you have one. An extended center column basically turns a tripod into a monopod, which I personally think is a bit less solid than a tripod.
One final, indispensable piece of equipment: a small flashlight with a red lens if possible, but some form of light to help with camera setup and adjustments in the dark. You don't need a lot of light but you definitely need some and the red lens helps preserve your night vision (and can be useful for lighting objects in the near foreground during image captures). Here's a look at my wife "painting" a hillside with a red LED flashlight during a capture.
Camera Settings and Technique
The first order of business is to pre-focus your lens at infinity, and do so while it is light outside -- your camera's autofocus won't be able to acquire focus with a night sky and manual focus on stars is virtually impossible to get right. Set your camera for single (not continuous) AF, pick the most distant object or horizon line you can see and acquire focus, then shut off the camera. If the lens has an AF/manual switch, set it to manual after shutting off the camera -- and do the same to the camera. The idea here is to prevent the focus point of the lens changing from your established setting.
Being careful not to move it, tape the lens focus ring to the lens barrel at three or four points to provide additional protection against changing the focus point -- apply the tape perpendicularly across the focus ring, but leave the zoom ring free if one is present. I personally use gaffer's tape for this step, as it secures the lens well and doesn't leave a sticky residue on the lens when removed -- I've had tape on the lens for weeks and it comes off cleanly. You might find gaffer's tape at Home Depot or similar stores, and I actually got my last roll at our local Calumet camera store -- but you may need to go online to find it.
Most lenses do better optically if you don't shoot them at maximum aperture, and I close my f/2.8 down to f/4 for night work, at least in part owing to the excellent high ISO noise performance from the D3s. Even if you only close down a fraction of a step, pixel peeping may show some image gains as you move off of maximum aperture. Shoot manual exposure, which makes you responsible for setting both aperture and shutter speed (taking the camera out of the exposure equation) and use the mirror lock-up before each shot if available. Auto white balance seems to work fine, and shoot RAW files if your camera has that ability. The nice thing about shooting RAW files is you have much greater leeway in post processing to fine tune the final image
I disable all noise reduction in the camera, which in the case of the D3s includes both high ISO and long exposure NR settings. Even when shooting RAW files, most cameras will perform noise reduction on images after capture and this can slow your ability to make another capture as the camera performs NR. Leave noise reduction to the post processing phase.
800 ISO is my usual starting point and I'll adjust from there as needed to get the exposure I want. Here's where a really fast wide angle lens like the 24mm/f1.4 models available from Nikon and Canon (and the Sony 24mm/f1.8) come into their own -- close down a full stop or even two and you're still at f/2.8 or thereabouts, which may allow you to shoot a lower ISO to obtain pleasing results. Remember, we don't want to go longer than 20 seconds to avoid star trails or open the lens to maximum aperture, so ISO becomes the main exposure adjustment in this style of shooting, given our self-imposed constraints on camera settings. Once the exposure is dialed in, with the lens at a fixed focus point you're left with little more to do than keep tripping the shutter to capture images and/or reposition the camera or change lens focal length for image composition. That's our goal -- to set up the camera so it requires little if any ongoing adjustment during image capture. Then you can just sit back with your coffee (or other adult beverage) and take in the beauty of the night sky as you fire away.
While the stars provide their own illumination, the same cannot be said for the earth at night. Knowing the moon phase and times it rises and sets are key factors in providing lighting on the ground features you may wish to incorporate into a shot. Objects in the immediate foreground may be lit via your flashlight or other means, but wide expanses of distant scenery require help from above. Just as with the sun, the moon moves across the sky owing to the earth's rotation and depending on the orientation of the terrestrial subjects in your shot you may want to shoot early or late at night. A full moon reflects a surprising amount of sunlight -- in a dark sky setting you may see distinct shadows from ground features -- and it tends to mask dimmer stars in the sky. Partial moon phases still provide a fair amount of light (especially considering the long exposure times) without masking so many stars. You generally don't want to have the moon in the frame when you shoot, as the direct light over the course of the exposure is too bright. You can use a large piece of cardboard to provide additional shade for the front lens element if the moon location could throw light directly onto the lens, but make sure to keep the cardboard out of the frame. Here are recent shots of Old Faithful geyser in Yellowstone and Badlands National Park in South Dakota -- the lengthy exposure lends a blurred, soft look to the geyser's water and steam plume while the yellowish light patch on the horizon at Badlands is the town of Wall, about 12 miles distant.
But the moon is not necessary to do night sky work, and in the case of events such as meteor showers no moon is an advantage as the sky is darker and makes meteors stand out better. Shooting meteors is like fishing -- you sit there making 20 second exposures continuously and hope a meteor flies through the frame. Here's a 2012 Geminid meteor capture.
There are a number of meteor showers annually when the number of visible meteors may increase dramatically for a day or two, and radiate from a particular section of the sky, making targeting them a bit more scientific than just random chance. An internet search will provide plenty of information on dates and times. But meteors aren't the only photo-worthy objects in the night sky, and some of the others keep to a schedule. NASA's website has a "Spot The Station" feature which provides dates and times when the International Space Station is visible from your location, and the "Heaven's Above" website can provide data on a number of satellites and other objects. Here are links to both.
One interesting subject listed on Heaven's Above is the "iridium flare". Iridium communications satellites use large solar panels to generate power, and under certain combinations of orbital path and sun angle can produce a short-lived but bright reflection visible from the ground -- the "iridium flare". The position in the sky and time of the flare event can be calculated with great certainty and thus these satellites (and the Space Station) are the best opportunity for a "sure thing" in night sky photography. The iridium flare typically involves the satellite coming into view as a small moving point of light for a short period, then increases in brightness over a period of maybe 10 seconds before dimming back down. The goal is to capture the satellite just before brightening, through the "flare" and then as it dims back down -- and it's tough to time your exposure exactly. Here's a flare near the Big Dipper that I caught just a bit too early.
There you have it -- just because the sun goes down doesn't mean you can't go out and make some interesting images in the dead of night. Hopefully these suggestions may provide few more tools for your photographic repertoire.