Jul 142011

The night sky from our camp in Botswana. The camera is pointing toward the Southern Cross and the trees are lit by the campfire. 15 minute exposure.

Night photography can be fun and rewarding and with digital photography it can also be easy to achieve great results.

You will need a tripod and a remote release, preferably one with a timer and a fully charged battery in your camera. A fast lens such as 50mm f1.8 would be useful but not essential.

The first thing to do is to find a suitable location, somewhere with a wide view of the sky and with  a strong foreground element such as a tree would be perfect.

Next, plan when to go. When the moon is full, it will light up your foreground but the stars will be dim. During the new moon, the stars will appear brighter but you may need to light up your foreground element with flash or a flashlight.

Next, plan which direction to take the photograph. If you are pointing North or South then the stars will create concentric circles around a point.

For focusing, use Liveview if you have it and focus manually. If you don’t have Liveview then manually focus the lens to infinity and make sure that you are far enough away from the foreground element so that it is in focus. This will be easy to achieve with a wide angle lens.

Turn off any vibration reduction or image stabilization.

The Northern Lights above Watchee Lodge. 30 seconds at f4, ISO 320.

Now for the tricky part, working out the exposure. I strongly recommend doing a test shot with a fast lens and high ISO first and then calculating the actual exposure.

The reason for doing this is to save time later. Assuming that you have ‘long exposure noise reduction’ switched on, then after your long exposure, your camera will be busy doing a black point calibration and this can take 50% to 100% of the time that was taken for the photograph.

E.g. If you do a 20 minute exposure, the black point calibration (long exposure noise reduction) will take 10 to 20 minutes. This means that your camera will be busy for 30 to 40 minutes. If you didn’t have the correct exposure then you’ve wasted a lot of time!

Lets assume that our goal is to have short star streaks. This will take a 15 minute exposure. We also assume that we want an aperture of f4 and 200 ISO.

Most digital SLRs have a long exposure of 30 seconds. In manual mode, set 30 seconds and f4 for the exposure.

The difference between a 15 minute exposure and a 30 second exposure is 5 stops: (8 minutes, 4 minutes, 2 minutes, 1 minute, 30 seconds) i.e. halving or doubling the time is 1 stop.

Therefore in order to have the same exposure at 30 seconds we need to increase the ISO by 5 stops (400, 800, 1600, 3200, 6400).

Now take a photograph at 6400 ISO, f4 and 30 seconds. If the photograph is too bright then try again at f5.6 or f8. If it is too dark then try f2.8 or increase the ISO.

Assuming that the best exposure was 6400 ISO, f5.6 and 30 seconds. All you need to do know is set 200 ISO, f5.6 and bulb.

Wait a minute, what on earth is ‘bulb’? Bulb is a shutter speed setting that is used for shutter speeds longer than 30 seconds. You usually need to be in manual mode to set the shutter speed to ‘bulb’. The shutter will open when you press the shutter release and it will close when you take your finger off the shutter release.

Due to camera shake and finger fatigue, you probably don’t want to hold the shutter release down for 15 minutes! This where the remote release comes in useful. If you have a remote with a timer then set the timer to 15 minutes and take the photograph. It will close the shutter once the timer has counted down. Otherwise, press the remote release and lock the switch. Use a watch and after 15 minutes unlock the remote.

You should now have a great night photograph! Good luck and let me know how you got on.

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