The night sky has been an important part of humanity and civilization for tens of thousands of years. The Pleiades (Seven Sisters) have been used as a vision test for thousands of years: seeing six with the naked eye indicates perfect vision and seeing seven indicates above-average vision. However, the inventions of electricity and artificial light have somewhat robbed us of the mysteries of the celestial bodies through light pollution over the last few hundred years.
But where technology taketh, technology also giveth. We may have more light pollution overall, but you can now take a digital camera out to a dark part of the world and end up with amazing results of the Milky Way. Here are some tips for how to take pictures of stars and capture the beautiful night sky.
When to Shoot the Night Sky
While technically viewable year round, you’ll have the best luck to get great photos of the night sky during the “high season” of March thru October in the northern hemisphere. You’ll want to plan your shoot around the new moon, when the sky is as dark as possible. You’ll find the Milky Way rising from the west. I like using the free open source planetarium software Stellarium to walk through where the Milky Way will be ahead of time — you can advance the software date into the future and time of your shoot.
Scouting a Location for your Star Photography
It’s important that you set up shop in a truly dark area for peak star photography. Use a site like Dark Site Finder to scout out a dark-blue or black region near you. This is the most important step! You’ll also want to check the weather report the day of your shoot to make sure you won’t be interrupted by clouds. If it’s a risk, you might want to come up with a few back up locations. And dark spaces often mean no cell phone signal! So plan accordingly.
Alternatively, you can search Flickr or Instagram for ‘milky way’ and see where other photographers have had luck and plan your shoot around that. Besides optimizing for dark sky, you might also want to put an interesting subject in the foreground for aesthetic value.
Camera Gear for Star Photography
Any camera that lets you change the shutter speed will work, even an old Canon Rebel. Certain models have a “Long Exposure Noise Reduction” feature that I highly recommend to make your photo less noisy. If you’re interested in Milky Way photography, make sure your camera supports this. Larger sensor cameras are also less noisy than smaller (full-frame versus micro 4/3s, for example). Recent Sony cameras have done better in low light with noise reduction (Sony’s A7sii is especially well known for its nighttime skills).
As for lenses, you’re going to want a fast wide-angle or fisheye: probably in the less-than 20mm range for a full frame, and f/2.8 is going to be ideal. You might not get a crisp shot at the widest your aperture can open, so it’s important to start with as wide as you can before you stop it down. You won’t need to worry about the shallow depth of fields at something like f/2.8 because the focus will be at infinity.
You’ll be shooting long exposures of 10+ seconds, so a tripod is an absolute requirement. An external shutter or intervalometer is also helpful (especially if you plan to stack your photos), but not strictly necessary.
Long Exposure Noise Reduction
You’ve probably noticed that shooting in a high-ISO mode can produce a very grainy or noisy look. You may have also noticed that shooting a long exposure introduces noise. The main source of photographic noise is from heat generating on the image sensor itself, and creating thermal electrons that interfere with the photoelectrons coming through the lens. Long exposures introduce noise because the sensor has more time to heat up, and high-ISO introduces amplifies noise.
Long Exposure Noise Reduction (LENR) is an option to correct for this noise in certain circumstances. If you take a long exposure with the shutter closed, you won’t end up with a perfectly black picture — you’ll get some noise. If you take a picture like this immediately after your exposure, the black-noise photo can be “subtracted” away from the main photo. And that’s exactly what this feature does: when enabled, it will take your long exposure and then immediately close the shutter and take another internal “dark” picture to correct for noise. Remember that this means it will take twice as long as your shutter speed to snap a photo.
Armed with LENR, set your camera to manual mode and dial in a starting point: shutter speed of 30 seconds, aperture wide open, and ISO typically at or around 3200. The “rule of 500” for astrophotography dictates that you divide 500 by your focal length; e.g. 500 / 24mm =~ 20s shutter speed, so based on your lens you may want to try a faster shutter speed than 30s.
After taking your first picture, you can try variations on shutter speed and ISO for intended brightness. This should go without saying, but also make sure you’re shooting in RAW mode or you’re just throwing away the full capabilities of your camera and the most helpful information for this image. To help with focus, put your camera in “live mode”, zoom in, and manually focus on the brightest star or a visible object in the foreground.
If you plan to stack your photos to reduce noise, you’ll want to use your intervalometer to take five to fifty of the same framing of the Milky Way.
Image Stacking in Photoshop
LENR is a great start for noise reduction, but there are even smarter ways to reduce noise. To image stack, you take multiple copies of the same framed long-exposure photos and combine them in Photoshop using a median averaging method that mathematically averages out the noise. It’s important to remember that your upper bound on number of photos to stack will be how many photos your computer can fit into RAM: you’ll run into a world of slow hurt if Photoshop needs to swap from hard drive into RAM. For more info on photo stacking, check out this tutorial: