The shutter is an electronically-controlled, mechanical device that opens briefly to allow light to fall onto the sensor. The period for which the shutter is open is called the “shutter speed” and for a typical camera varies from a few seconds down to about 1/2,000th of a second or shorter. An animation of shutter operation is provided: Shutter animation
Freezing the action
Setting the shutter speed controls the amount by which subject action is “frozen” or conversely the amount of creative motion blur. Judging the required shutter speed is largely a matter of experience, as the shutter speed to freeze a subject’s motion depends on its speed, distance, the direction of travel and so on. We may not wish to freeze the motion completely; for example if photographing a tennis match, we may wish to freeze the players but show some motion blur in the racket and certainly in the ball.
As a starting point, typical shutter speeds for different activities might be:
|Portrait||1/60 to 1/250 s|
|Street||1/125 to 1/350 s|
|Walking people or animals||1/500 to 1/1000 s|
|Sports or running animals||1/1000 to 1/1500 s|
|Flying birds||1/1500 to 1/3000 s|
One thing that is guaranteed to ruin a photo is camera shake – caused by setting a shutter speed too slow for a hand-held shot. While motion blur is often creative, blur due to camera shake is usually a disaster. To avoid camera shake, set a shutter speed at least as fast as the lens focal length. For example when using a 50mm lens, use shutter speeds of 1/50 second or faster (1/60 second or faster in practice).
To use slower shutter speeds than this, a tripod or other means of steadying the camera is needed. Many cameras and lenses these days are fitted with an image stabilisation system that counteracts the small vibrations inherent in hand-holding the camera. With a stabilised lens, it is typically possible to take a sharp hand-held shot at shutter speeds 2 or more stops slower than the normal rule of thumb.
There are many ways to set up a modern digital SLR. The following technique was described to me by Jonathan Perugia as a good “safety setting” or starting point especially for street photography.
Tv. When strolling about with no particular shot in mind, set shutter priority mode “Tv” with a shutter speed that should avoid camera shake for the maximum focal length of the lens in use. For example if using a 24–70mm zoom, set a shutter speed faster than 1/70 second, say 1/125th or 1/250th. Now if a scene suddenly appears and there’s no time to think, the settings will allow for a quick grab shot with a reasonable chance of success.
Av. A similar logic can be used by those who prefer to use aperture priority, “Av”. The minimum shutter speed can be preset in the camera’s menus. For Canon cameras it is within the “ISO speed settings” menu and it can be set to a fixed value or set to auto. In auto, the camera will select a minimum shutter speed at least as fast as 1 / lens focal length. This is particularly useful for a zoom lens with a wide range of focal lengths, as the camera will constantly adjust the minimum shutter speed to avoid camera shake for the focal length in use.
When choosing which shutter speed to use, we need to consider the amount by which we wish to freeze or blur subject motion – while always avoiding blur due to camera shake. If I take the example of street photography using a typical mid-range zoom lens of 24–70mm, I would probably want a shutter speed around 1/125 to 1/350 sec. These speeds would avoid camera shake and take sharp images of static and slowly moving subjects. A little motion blur might creep in for faster subjects and this might be acceptable, even desirable.
The simplest way to achieve this is simply to select “Tv” and set the desired shutter speed. An alternative is to select “Av” and set the minimum shutter speed in the camera’s menu to 1/125 sec. Some pros and cons of setting Tv or Av are:
|Tv||Immediate control of shutter speed if some “drama” occurs||Inability to quickly adjust depth of field via f/number|
|Av||Creative control of depth of field is always available||Inability to quickly increase shutter speed if needed|
For a more detailed discussion of Av versus Tv see: Tv vs Av