A camera uses shutter speed to regulate how much light enters the lens.
In modern photography, three factors determine how much exposure a particular media such as film or a digital sensor receives. The ISO, the aperture and the shutter speed comprise these three factors and they have a direct relationship with one another. When a photographer adjusts the shutter speed, he must make a corresponding adjustment to one of these other two settings to give the media the same amount of exposure.
The Camera Shutter
Inside of each camera is a device known as the shutter or shutter curtain. It functions in a similar manner to the shutters on a house. When you open the shutters, you let light into the house; close the shutters and no more light enters. If you open the shutters quickly, only a minimal amount of light enters the house, but if you open them and leave them open for an extended time, more light enters the house. A camera's shutter performs the same way. When the photographer presses the shutter release button, the shutter curtain opens for a predetermined duration. The duration of time the shutter remains open is called the shutter speed.
Types of Shutters
Two basic types of shutters exist -- the focal plane shutter and the leaf shutter. The focal plane shutter is in the rear of the camera, directly in front of the film or digital sensor. Focal plane shutters travel vertically or horizontally across the film plane. Leaf shutters are found in the diaphragm of a lens. In a lens with a leaf shutter, the aperture serves two purposes -- it regulates the amount of light entering the camera through the selected f/stop and it serves as the shutter, regulating the shutter speed. Leaf shutters are most popular in large-format-view camera lenses.
Shutter Speed
Modern cameras have shutter speeds that range from 30 seconds to 1/4000th of a second and faster. As part of the exposure triangle, the shutter speed determines how long a camera's film or sensor is exposed to light. Shutter speed also determines whether movement is captured as frozen movement or fluid movement. The faster the shutter speed, the more easily movement is frozen in time. For example, a shutter speed of 1/1000th of a second can easily freeze the movement of a baseball player striking the ball with a bat. A shutter speed of ½ second would render that same image a blur.
Other Factors
The other two factors that influence exposure are the aperture and the ISO. The aperture sits inside of the lens and opens and closes like the iris of the eye. It regulates the amount of light entering the camera via a selected f/number or f/stop. The ISO determines the light absorption characteristics of the media (film or digital sensor). The higher the ISO, the more light the media absorbs; the lower the ISO, the less light the media absorbs.
Tags: light enters, shutter speed, shutter speed, amount light, digital sensor, film digital, film digital sensor
