Along with aperture (size of lens opening) and ISO (light sensitivity of the film or sensor), shutter speed is the third element that makes up the "exposure triangle". These three elements work together to get the right exposure. Open the aperture by one stop and the shutter speed will move down a stop and visa a versa. Move the ISO up and your shutter speed can be increased or aperture decreased.
Shutter Speed Explained: In film photography it was the length of time that the film was exposed to the scene you’re photographing and similarly in digital photography shutter speed is the length of time that your image sensor is exposed to the light coming from the scene you’re attempting to capture.
Shutter speed is measured in seconds and more commonly in fractions of seconds. The bigger the denominator the faster the speed (i.e. 1/1000 is much faster than 1/30). If the camera is on a tripod and the subject is not moving, such in most landscape work, shutter speed doesn't matter much except to be fastest enough to stop trees blowing in the wind. Handheld, shooting sports or moving children, fast shutter speed becomes crucial to stop the motion.
How fast do you need? Handheld shutter speeds of 1/60th of a second or faster. The rule is to match the focal length of the lens you are using. For example with steady hands a 24 mm lens can be hand held at 1/24th of a second, while a 200 mm is going to need a shutter speed of at least 1/200th of a second. A Good rule of thumb is to try to have at least a 1/125th of a second shutter speed. Anything less is going to lead to camera shake i.e. blurry photos.
Lens and cameras with some type of image stabilization (more and more cameras are coming with this built in) can allow you to use slower shutter speeds.
Shutter speeds move by stops or double the time for example 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8 etc. This ‘doubling’ is handy to keep in mind as aperture settings also double the amount of light that is let in – as a result increasing shutter speed by one stop and decreasing aperture by one stop should give you similar exposure levels
Very slow shutter speeds in seconds can be used for long time exposures for bluring water, moving car lights at night or star photography. Most cameras also give you the option to shoot in ‘B’ (or ‘Bulb’) mode. Bulb mode lets you keep the shutter open for as long as you hold it down.
In landscape photography, aperture might be the setting you are most concerned with but in sports or with anything moving, shutter speed might take priority.
Faster shutter speeds freeze movement while slower shutter speeds allow the motion to blur. You can try panning technique in which a slow shutter speed is used and the camera follows the action. The result is a sharp subject with a motion blurred background.
Or you can keep the camera still, using a tripod and letting the motion in the scene blur like the water in this waterfall.
Credits:
Created with images by Mike Wilson - "Light trails over urban road" • 4924546 - "volcano water drip" • Veri Ivanova - "Old pocket watch" • RonaldPlett - "speed curve corner bike" • dimitrisvetsikas1969 - "car vehicle hurry" • Robin Pierre - "S like Speed" • Joshua Reddekopp - "Snowboarder at resort"