Shutter speed, which affects motion blur, is one control of camera exposure.
Camera exposure is the process by which light enters a camera and creates an image on the film or digital sensor. The main exposure controls in a camera include aperture, shutter speed and ISO (film speed or light sensitivity). Most cameras contain a light meter that judges the amount of light present and either sets these controls for you or lets you know alter the controls yourself to change the exposure.
Aperture
Aperture controls exposure by allowing light to pass through a diaphragm whose width is changeable. Aperture numbers are marked by the designation "f/," as in an aperture width of f/22. Large aperture numbers such as f/22 let in a very small amount of light, while smaller numbers like f/1.8 let in more light. The visual result of using f/1.8 is a shallow depth of field: the portion of the image that you focus on will be sharp but other depths of the image will fall out of focus. Using f/22 makes it more likely that both the foreground and background of your image will be sharp.
Shutter Speed
Shutter speed affects exposure by controlling the length of time light falls on the film or sensor. One second is considered a slow shutter speed, while 1/2000 of a second is fast. Moving objects photographed at one second will appear blurry in the image, while capturing the object at 1/2000 of a second will likely freeze its motion. A setting of "B" which stands for "bulb" is also possible -- this means that the shutter stays open as long as your finger holds down the exposure button. A longer shutter speed creates more exposure.
Light Meter
Light meters let you know if your chosen combination of aperture and shutter speed is enough to make a proper exposure given a particular light situation. Light meter displays vary. Some may be as simple as a needle that points towards a plus or minus sign which indicates you need more or less exposure to make an image. The needle rests on a dot in the center of the plus and minus once you achieve the proper exposure. Other light meters display as a series of bars that spread underneath plus and minus signs when the exposure is off, and display as just one bar under the center dot when exposure is correct. Point-and-shoot cameras usually do not display any visible light meter, determining exposure and adjusting controls on their own.
ISO
A digital camera's ISO setting adjusts its sensitivity to light, or informs the film camera what speed of film you are using. Its role in exposure is to make sure the film camera is correctly reading the amount of light needed to make the proper exposure, or to boost the digital camera's light sensitivity, which changes the aperture and shutter speed suggestions. A low ISO number, such as 50, indicates a slow film or low light sensitivity, creating the need for longer shutter speeds or wider apertures. A high ISO number like 3200 means the film or digital camera can operate under low-light conditions. Thus, you can make proper exposures using faster shutter speeds or smaller apertures.
