The shutter speed also known as exposure time, is the length of time that a shutter allows light through the lens of a camera and onto the sensitive surface be it a digital sensor or piece of film.
It forms part of the Exposure settings , alongside this are ISO (sensitivity), and Aperture (the size of the hole). These two and the shutter speed can all be changed so as to give the ideal combination for an exposure.
The agreed standard shutter speeds that should be present on all cameras are:-
Many cameras however go far further above and below this. The Nikon D300 for example going from 30 seconds to 1/8000.
The sequence of speeds used above are historically based in mechanical shutters. They can be considered as being 1 stop apart, each doubling or halving of the one above, although not exactly mathematically correct there are in effect three groups, 1 to 1/8, 1/15 to 1/60 and 1/125 and above. Today many think this has been retained in part because no one wants to be the one to change and partly as it is easy to remember, at least the upper and lower ranges, and you end up with a logical sequence of numbers. The numerical differences are proportionally small and should have no real affect on the exposures.
In addition to these you have one or more settings to allow longer time exposures to be made these are marked T for time or B for Bulb, the difference between these is that with Time (T) you press the shutter release twice once to open and once to close, while with Bulb (B), you hold the shutter release for the period of the exposure. These are located at the bottom end of the shutter range next to the slowest speed. You often have to set modern DSLR cameras to manual mode, before they show up. B is far more common on modern DSLR's than T.
To manage a longer time exposure you can use a special cable release with a timer built in or use the lock feature on the majority of cable releases. This lock feature is often a sliding mechanism so you press the shutter release on the cable and slide it to lock and slide it back to the release position to release the shutter.
Another way to get the effect of longer exposure is to add together a number of shorter exposures with the camera on a tripod, and many cameras have this ability.
Which shutter speed to use
There are a number of factors that affect the best shutter speed or shutter speed range that you wish to use, although often its the balancing factor that gets varied, without a lot of thought when you have already set the ISO and are selecting the ideal Aperture or are using aperture priority mode on your camera.
The factors to consider are:-
Shutter Priority Modes
Most cameras have a shutter priority (S) mode, other common modes are aperture priority (A), programme (P) and manual (M). In shutter priority mode you set the shutter speed and the camera sets for you the aperture, using the information from your exposure metre. Exposure variation allows the image to be darker or brighter. Shutter Priority mode is most frequently used with sports and water photography. Manual being the preferred method for photographing fireworks and light traces.
Most cameras have a self timer facility, this allows the shutter to be fired after a delay. This is useful when you want to get into the photo, but is also useful when you want to fire the shutter without shaking the camera. Many cameras have the option to change the delay with a short period such as 2 seconds for this use.
for details on Exposure Article Route see the Exposure page