Astral Photography: How To Shoot the Night Sky

By Matthew Braga

Astral photography is perhaps the most difficult style of picture taking to master, but with the right settings, its easy to capture the night sky's magic.

If you're one of the lucky folks living in the far northern half of the world, an impressive light show might be coming your way this evening. Solar flares on Sunday launched huge bubbles of plasma hurtling towards the Earth's atmosphere, which should make the aurora borealis — or northern lights — much more prominent than usual.

Astral photography is perhaps the most difficult style of picture taking to master, requiring a great deal of patience and trial and error to get good results. But with the right settings, it's easy to capture all sorts of objects in the night sky, from meteors to satellites, and even the Milky Way.

bulb mode. Usually, your camera's shutter is only open for just a fraction of a second, which prevents an excess of light from overexposing your photo. However, at night, there's far less available light than during a daytime shoot, allowing the shutter to stay open for a much longer period.

To get started, you'll want to pick a nice open space — one where your camera can easily see a large, visually interesting portion of the night sky. Areas with the north star in view are often popular choices, as all the stars will move around that central point. Just be wary of things like radio towers, lamp posts or other distant sources of light, which could disrupt any potential photos. 

On the technical side, you'll need to know your way around your camera's manual mode. We've covered this before, but manual will let you adjust things like shutter speed, aperture and ISO — all very important in producing a successful night time image. Just don't forget a tripod.

Know Your Shutter Speed

116 two minute exposures. 800 ISO. f/4. Via Flickr user *BZd*.

As for how long to keep your shutter open, there's no hard and fast rule. In darker areas where there's little light pollution, you can keep your shutter upon longer, sometimes for over an hour. If you're capturing stars, this should result in longer trails, which can make for a more visually interesting picture. However, if in an area with more ambient light — near a city, for example — a shorter exposure might be necessary to keep stars or other celestial objects visible. Your best bet is to start with an exposure of around five to ten minutes, and move up from there.

Keep Your Focus

Another important key to good long exposures is making sure your focus is set correctly. That is, you'll need to ensure manual focus is enabled and set to infinity. This ensures that the night sky will stay as sharp as possible, and not the objects closest to you. 

Pick the Right ISO

Setting your ISO correctly depends on a number of factors. Many digital cameras perform poorly in dark situations, especially where long exposures are involved. Adding a higher ISO into the mix — which is essentially digital gain control — can make that grain much, much worse. The lower the ISO, the less grain in your final image, though the longer your exposure will have to be.

However, taking long exposures with a higher ISO does have its place. Many deep space objects that might not be visible with lower settings, and will reveal themselves only with a higher value. In fact, some photographers suggest taking long exposures at 800 ISO or higher, which has the added side-effect of decreasing the amount of time you'll have to keep your shutter open. If you have a newer camera with a decent sensor, higher ISO settings are definitely worth a try, but don't be disappointed with the results are too grainy to be used.

Watch Your Depth With Aperture

Here, the aperture is small enough that the silo is still in focus.

For example, things like windmills, trees or other objects can make night time images much more interesting, especially when silhouetted against a dark night sky. However, a narrow depth of field may leave these objects blurry, while keeping the stars in focus. It's for this reason that you'll want to shoot for something a little wider — at least f/5.6 or more. Just remember, the higher you dial your aperture, the darker your image will become, and the longer it will take to capture an image, so balance it accordingly with your shutter speed and ISO settings.

Loose Ends

 This image, taken on my Canon 30D, went through long exposure processing.

If you find your camera producing lots of bright pixels during night time shooting, you have a few options. Turning on long exposure reduction, or a similarly named setting, will have your camera process these hot spots out, leaving behind a more natural looking image. However, the trade off, especially with older Canon cameras, is that it takes *twice* as long to process the final image. For a half hour exposure, that means another whole half-hour before another picture can be taken.

Long Exposure Noise Reduction on some Canon models. 

Finally, it should go without saying that anything you shoot should be taken in RAW. As great as JPEG is, you'll want to save as much of the original image data as you can, especially if you need to edit out hotspots or make lightning/exposure adjustments later on. You'll be kicking yourself otherwise.

As you can probably tell, there's no exact science to making any of these settings work for you — it all depends on your location, and the type of object you'll be shooting. Done right, you can produce some amazing results, from super-long star trails to colorful, sun-induced light shows. Just make sure you share with us anything you shoot, and tell us if you have any tips of your own! 
Images via Flickr users ccdoh1, Scott Butner and Adcuz.