shutter speed

The duration during which a camera's shutter is open and the film plane is exposed to light. These speeds are rated in terms of 'stops', each stop being being a duration twice as long as the previously slower one... Thus: 1 second, 1/2 of a second, 1/4th, 1/8th, 1/15th, 1/30th...etc...

Certain minimum shutter speeds are necessary in order to stop certain kinds of action from appearing as movement in a photo. For example:

• 1/30th of a second is usually recommended to stop camera movement.
• 1/60th will stop a person walking at a fast pace.
• 1/125th will stop someone gesturing wildly.
• 1/250th will stop a slow moving car and flowing water.
• 1/500th will stop a rapidly moving car and turn a waterfall into individual droplets of water.