Night photography

Night photography may seem like it’s complicated but that’s not the case, just a few principles are needed, some trial and error and a little patience. It’s extremely rewarding after putting in some effort and time to see what’s possible when you get it right.

Stars or star trails

When photographing the moon, stars and constellations your choices are taking a short exposure of typically less than a minute to capture the sky, Milky Way or meteors or take a long exposure of many minutes or hours to capture star trails.

Stars, Milky Way and meteors – short exposure

As the earth rotates, the stars appear to move across our skies. You can’t see the stars moving but it’s significant enough to streak the stars in a timed exposure. To avoid stars moving in our images we can use what is called the 600 Rule to calculate the length of an exposure.

By dividing 600 by the 35mm focal length equivalent of the lens we arrive at the maximum number of seconds for our exposure. For example using a 28mm on a full frame camera would allow 600 / 28 = 21 seconds of exposure time without apparent star streaks. With a 1.6 crop factor camera the time would be 600 / (28 x 1.6) = 13 seconds. The longer the focal length, the shorter time you have.

After calculating the time the only variables to play with for a correct exposure are the aperture and ISO. By using the maximum aperture (smallest f/ number) you can use the lowest possible ISO to minimise high ISO noise.

 

Star trails

A long night time exposure will result in stars tracking across the sky. The length of trail will depend on the focal length of the lens used, the exposure time and importantly where you are looking in the sky. In the northern hemisphere Polaris, the North Star, is the star around which all stars rotate. Moving south from Polaris the more apparent movement you will record in your frame to a maximum over the equator.

Exposures longer than 30 minutes are best. Calculating the aperture requires a bit of trial and error and depends on how long an exposure you want and how much ambient or moonlight is present. A good starting point for a 30 minute exposure on ISO 100 is f/6.3. It’s actually hard to over-expose on a dark night.

Shooting the moon and by moonlight 

The best time to photograph the moon is when it is low on the horizon. Just after sunset or before sunrise is good when there is colour in the sky. As the moon rises any haze or pollution in the atmosphere can add a beautiful colour tint to the moon.

To get a decent size moon in your frame you will need to use a long lens, preferably 200mm or longer. This is good for capturing the moon against a silhouetted skyline, tree or mountain.

To get the correct exposure to capture detail on the lunar surface, meter directly off the moon itself, it is surprisingly bright. As a starter for a full moon try ISO 100, f/11 and 1/125. The moon moves approximately its own diameter every 2 minutes. This means you need to use a relatively fast shutter speed to avoid blurring.

Photograph the moon as a crescent or when it’s partially full to best capture side-lit craters and mountains.

The amount the landscape is illuminated by the moon depends on it’s phase and position. The moon can be bright enough to cast shadows and even, if there is mist or fog, create moonbows.

Camera considerations

Most cameras will have settings that allow exposures of up to 30 seconds. This is adequate for some night shots but for star trails especially you will need to use a B (Bulb) setting with a cable release to enable exposures of minutes or hours.

Full frame cameras do best here, normally the larger the sensor the better the low light capability.

Some tips for night photography

• Find the darkest skies possible and try to avoid light pollution from towns. Don’t forget your torch.
• Ensure batteries are fully charged.
• Use a good tripod weighted down if it’s windy.
• Use a remote shutter release or self timer and mirror lockup (SLRs only) to reduce camera shake.
• Autofocus on a bright object like the moon before exposure then turn autofocus and image stabiliser off to avoid blurred shots.
• Frame your shot using the highest ISO as a test shot before dropping the ISO to the lowest usable setting.
• Exposure times can vary from a few seconds to many hours depending on the subject.
• Long exposure noise reduction or dark frame extraction. This is a function in most DSLRs and works by taking a second exposure of exactly the same length as the first with a black screen. Any noise appearing on the dark, second, exposure is subtracted from the first.  Rather than wait a long time before you can take the next shot, turn off noise reduction and fix later using software.
• Some cameras have a virtual horizon to level the camera.
• Shoot RAW – easier to correct white balance and exposure if you need to make a shot lighter or darker.
• Use the histogram to check exposures, at night the rear preview screen may show a bright photo in the dark when it’s actually underexposed.
• Use the widest and fastest lens for capturing stars and sky without star movement.
• Know your camera controls, using a torch will spoil your night vision.
• Turn off all displays and anything that may reduce battery life.
• Dress warmer than you would expect, you will spend a lot of time hanging around. A flask with hot drink is very welcome on a cold night.