Dark Sky Photography

A night photographer’s introduction to long exposure shots

A lot of astrophotographers experiment with ‘star trail’ photography when searching for new techniques that take advantage of their existing equipment. It is a rewarding approach for the first-time astrophotographer and the seasoned pro alike! The typical star trail photo is characterized by abstract geometry, surreal landscape, and a visual representation of time. They can also be a fun way to chronicle the movement of the Earth in time, and the relative movement of other bodies. What equipment and settings are needed to take a star trail photo? How long should an exposure be? In this article, we’d like to help the beginner get started with some answers to these basic questions so that he/she can jump right into the process.

Like some of you, when we first started taking astro photos, most of our work was characterized by short exposure times (less than 30 seconds) because we were trying to avoid star trails. As a result, we were faced with underexposed faint stars and general lack of detail. A lot of this was due to us being forced to open our lens apertures as much as possible (i.e. f3.5) in order to bring in the most light. When you do this, you sacrifice image detail, introduce optical aberrations/distortion, and lose depth of field). We were learning the limitations of our setup and the effect of our viewing conditions. We also learned that star-trail photography was less susceptible to those shortcomings. A closed-down aperture and no limit on exposure length is something to look forward to for a change!

Equipment

Of course, you’ll need a tripod and a camera, but you’ll also need a cheap little device that plugs into your camera called an ‘intervalometer.’ Intervalometers for night photography can be had just about anywhere online for less than 25$ (see Amazon). Key features such as exposure duration from seconds to hours, delay, and interval should be standard to any model. Grab an extra battery while you are shopping. It is possible to take long exposure star trail photos using a remote or corded shutter lock, but don’t waste your time. Get an intervalometer and you’ll be happy later when you are also using it to take time lapses, timed photos, and tracking mount sets for post-process stacking.

Camera Settings

Just to make sure you’re off to the right start, switch your camera to Manual Mode and enter the ‘Bulb’ shutter setting. The Canon Bulb mode is found by turning the shutter duration wheel past the maximum allowable shutter duration. The Nikon Bulb mode is also found this way. Before you setup your shot, enter your camera’s menu and disable any auto-power-off features or you’ll be sorry! We recommend using a relatively wide lens. Try something with a focal length around 10-50mm. Longer lenses, such as telephoto lenses are generally out of their league and better left at home for now. Don’t worry about not having a ‘fast’ or fixed-focus/prime lens. In fact, a good star trail photo will have you closing your aperture to something in the f5.6 or f11 region. A higher f-stop setting will actually keep your image sharper and your foreground detailed for reasons requiring optics theory for explanation. For instance, we don’t shy away from using the popular Canon 18-55 f3.5 kit lens for star trail photography. Take that, 3000$ f1.4 lens!

With your camera on the subject (consider allowing 2/3 of your frame for night sky, and the bottom 1/3 for landscape), bring your lens into focus at infinity, and take a quick 20 second photo at high ISO and large aperture (i.e f3.5) in order to check your focus. Check your focus by making sure stars are as sharp as possible! See our article on Milky Way photography for more details on this process.

Now, adjust your settings for the big shot. We have compiled a brief work sheet of star trail camera settings below to help you get started. These are directly transcribed from a handful of star trail photos of ours and are included at page bottom. Bump up your ISO setting if you want to get more pronounced results. Also, please remember to include a 5 second delay on the intervalometer to dissipate any vibrations from your hand.

Recommendations

When your picture is finished, decide what you don’t like about it and make the adjustment. I guarantee you’ll wish those star trails were longer! Before cranking up the exposure time, keep in mind that your biggest enemy is going to be grain and noise in the photo – and it’s only going to get worse. A lot of this can be corrected for in post-processing software, but generally, just try to keep your ISO low and let your aperture approach the f11 region.

The key is experimentation and patience. You might only be able to take two or three really long ones in a night! Always have a record of your settings similar to the one we created for this article and that includes temperature and general viewing conditions. You’ll realize the payoff when you bag some surreal shots that you’re proud of. Night photography taken in proximity to an airport or distant roads, during a meteor shower, or even the Northern Lights can introduce exciting effects. Try ‘lighting up’ the foreground with a flashlight for a more prominent foreground, or perhaps insert yourself into the picture. Even very short star trails can accentuate faint star formations, making dim constellations shine.

Star trail night photography is great stuff to share with friends, family, or people interested in seeing what you do. It’s also a great way to take some impressive night sky photography while relaxing and drinking beer in your lawn chair! Cheers to the intervalometer!