What is it?
There is no real definition for a long exposure. My interpretation is that it is when you take a picture that lasts longer than a few seconds, and will almost always be mounted on a tripod.
How do I use it on my camera?
Most DSLR cameras will allow you to take a picture for 30”, which is 30 seconds. 30” can be found by using the Shutter Priority mode on your camera. You may also want to use the camera’s self-timer to release the shutter – that’s the mode that lets you get into the picture and waits 10 seconds before taking the picture, so that you don’t move the camera when taking the photo. If you want to take a photo longer than 30” you will need a shutter release cable and use the “Bulb” mode on your camera. These cables are relatively cheap (under $20 for entry level cameras) and are quite handy.
What does it do to my pictures?
The reason for using a long exposure is to usually capture scenes that are poorly lit, such as a night cityscape or the trails of car taillights driving down a road. They can also be used to remove moving things in your picture, such as people in a busy scene or fast moving water. Long exposure pictures of cities at night will only show parts of the image that stay still for the entire picture. During a long exposure of the Brisbane River, for example, a City Cat may move through your picture, but in the final image you will only see the lights on the boat as it moves through the picture.
The longer the exposure, the more that moving things will blur. With a fountain for example, if you use a fast shutter speed you will see the droplets mid flight, but if you take a long enough picture of the fountain, you will only see the water gushing upwards, not the water falling back down.
The picture on the right was a 10 second exposure; we used a filter, like a pair of sunglasses, to reduce the light. The fountain now only shows the water rising but not the water falling back. Note the water on the lake is also very flat – the ripples are almost gone.
This 30 second photo shows the taillight and headlight trails of the cars that were driving on the racetrack, but not the cars that were making the trails. You can see some parked cars in the pits in the top right of the picture.
This is a busy mall in Brisbane, but it could be any city scene. The constant flow of people will never stop. If you wanted a picture, without people a long exposure will help.
You can see the white “fog” through the middle of the picture; this is the “flow” of the people that have been blurred by the long exposure. Note that the white ”fog” was used to show the people moving, in a different composition without a bright centre spot there would have been no fog. Again a filter was used to reduce the amount of light coming in to the camera.
In this six minute photo, a few City Cats and river boats moved through the shot. You can see the light trails on the river, and you can also see the stars and the clouds moving through the sky.
Using the self-timer and a tripod, set your camera to shutter priority mode and take some shots longer than 10 seconds. Note that without a filter to reduce the light, you will need to find a very poorly lit subject. What aperture values do you need to get the longer exposures?