The shutter determines the duration for which the film or sensor is exposed to light. Typically, this will be measured in fractions of a second, although when light levels are low this can extend to seconds, minutes or even hours. Whilst the shutter is open, any movement by the subject will be recorded as a blur. This might be the desired result, but it is more usual to have the main subject sharp.

Neither is it the subject that can move, but the camera itself is susceptible to small movements when it is handheld. It is more usual for exposures to be made at 1/125 or higher to avoid the risk of camera shake. The general rule used to be that the shutter speed should be at least as high as the focal length in use, as any movement induced by the user will be magnified by a long lens. 1/30 of a second might seem like a very short period, but it is surprising how much movement can occur with either the subject or the camera in such a brief moment.

Recent developments in image stabilisation have altered this to an extent. Small gyroscopes mounted either in the lens or the camera detect small alterations in the attitude of the camera and move a special element in the lens or the sensor respectively to compensate. All clever stuff that allows slower shutter speeds to be used, although this remains limited to fractions of a second and anything longer requires the camera to be supported during an exposure.

The more traditional way to prevent camera shake is through the use of a monopod or tripod. Since a monopod is inherently unstable, unlike its tripod counterpart, it is only suitable for the same exposure durations as image stabilisation. For long exposures, a tripod remains the only option unless an alternative convenient resting place such as a wall can be found.

When using a tripod, a method of actuating the shutter remotely is desirable. Even with a camera firmly mounted on a tripod, it is still possible to move the camera by pressing the shutter release and get an image burred by camera shake. Traditionally, this was achieved with a wired cable release for older film cameras, but with the introduction of electronics, remote cable releases have become the norm. Wireless releases are also available, but a wired one is preferable.

The longest shutter speed for most cameras is 30 seconds, but when light levels are very low this is not always sufficient. A wired release allows what is known a “bulb” setting where the first press opens the shutter and a second closes it. When there is not much available light to make an exposure, accurate timing of the period when the shutter is open becomes less critical.