Photo Tip of the Week: Understanding Shutter Speed
While most DSLRs offers a host of controls and settings, there are really only three you need to worry about – aperture, shutter speed and ISO. In this series, we take a close look at each of these variables and see how they can be used to create better pictures. In this, the second part of the series, James Ostinga and Andrew Fildes examine the finer points of shutter speed.
Shutter speed is the amount of time, measured in seconds, that a camera’s shutter remains open. As you’d imagine the longer the shutter is open the more light hits the sensor. So, slow shutter speeds let more light into the camera than fast shutter speeds.
Apart from its role in controlling the amount of light that hits the sensor, shutter speed also affects the way the camera renders movement.
Movement
A fast-moving sports car photographed with a slow shutter speed, for example 1/15 or 1/30 second, will appear blurred as it speeds past the camera. Use a fast shutter speed, say 1/1000s, and the same car will appear as still as if it were parked on the side of the road. There's no right or wrong shutter speed. Sometimes the blurred look will be what you want to capture a feeling of dynamism in your pictures, sometimes it's better to freeze the action. Shutter speed gives you the option to make that creative choice.
Sports photographers mostly use fast shutter speeds, which allow them to
freeze fast motion. Because fast shutter speeds don’t let in much
light, the pro sports guys compensate by using lenses with wide apertures. Big
apertures translate to big lenses, which accounts for the size of the
lenses you see at big sporting events. If you don't happen to own an f2.8 telephoto lens worth several thousand dollars you can still use fast shutter speeds, just dial in a higher ISO.
A fast shutter speed freezes the action. In this image, taken at
1/8000s, you can clearly see the individual droplets of water frozen in
midair behind the skier. (Camera: Olympus E-3. Exposure: 1/8000s @ f/2.
ISO: 100. Focal length: 300mm equivalent.)
Blurry Water
The soft flowing water shot, commonly
seen in images of waterfalls, rivers and seascapes, is a classic – a
cliché even! Still, it looks great and it’s a useful way to get familiar
with the shutter speed control.
To create the effect you’ll need a DSLR and a tripod. With your camera
and tripod in position, turn your camera’s exposure mode dial to Shutter
Priority (Tv or S).
Select a slow shutter speed – somewhere between 1/4
and 10s should be enough though it depends on how fast the water is
moving.
Now, one of the challenges with this type of shot is that there may be
too much light to get the shutter speed you want. First, make sure the
ISO is set to its lowest setting, normally 200, 100 or 50 ISO. If it’s
still too light, you can artificially darken the scene with a neutral
density filter. These clever little glass accessories reduce the amount
of light that gets into the camera. They’re available from most camera
stores and come in a variety of shades -- simply position the filter in
front of the lens and dial up the new exposure settings.
Have a go at using the same technique on other subjects -- moving cars
at night, sparkler trails, long grass blowing in the wind.
As shutter speed slows, movement begins to show up as blur. LEFT: Anzac Bridge, Sydney. Canon EOS
450D, Canon 18-55mm IS lens @ 27mm (equivalent). Exposure: f/22 @ 1/12s, ISO 100. ND8 filter, tripod.
Photo by Peter Wilson-Jones, Triographic. RIGHT: Seal Rocks, NSW. Ricoh GR Digital @ 28mm (equivalent).
Exposure: f/9 @ 1s, ISO 100. Tripod. Photo by James Ostinga.
Shutter Priority (S, Tv)
With the camera set to Shutter Priority you choose the shutter speed while the camera automatically adjusts the aperture to obtain a balanced exposure. Use shutter priority if you want to control the way your camera records movement. If you want to show a moving object as a blur, use a tripod and choose a slow shutter speed. If you need to freeze the action, choose a fast shutter speed.
Get used to checking the f-stop display as you adjust the shutter speed. If you see the aperture setting flashing, it may be an
indication that the shutter speed setting you’ve chosen is too fast or slow and it's not possible to produce a balanced exposure.
With Shutter Priority selected, you’re free to choose the shutter speed while the camera automatically sets the appropriate aperture to balance the exposure.
Camera Shake
Camera shake can cause problems at slow shutter speeds, making images appear soft. And the problem becomes more pronounced with telephoto lenses and big zooms.
There are a few solutions. One option is to put the camera on a stable platform like a tripod or monopod. Another is to increase the shutter speed. A rule of thumb for hand-held shooting says the shutter speed should be at least “1/focal length”. For example, if you are zoomed to an equivalent focal length of 250mm, the minimum shutter speed should be 1/250s to ensure sharp images.
Fortunately, most DSLRs these days also offer some form of image stabilisation (IS, OIS, VR) which allows users to shoot sharp hand-held shots at slower shutter speeds – around two to four steps slower than normal. This gives you a bit of extra help, though there are still plenty of situations where you’ll find a good tripod handy.
Article first published in Digital Photography + Design, February-March 2010.
