EXPOSURE

Exposure in Photography refers to the film or digital sensor being exposed to the correct amount of light to produce an image with detail in the dark areas (shadows) and detail in the bright areas (highlights).

The key to correct exposure is the light meter, hand-held or built into the camera, all modern cameras have built-in light meters that measure the light entering the lens and sets the Aperture (f-stop) and shutter speed automatically, all of this is done when you press the shutter button.

Some cameras give you the option to set the exposure manually, you can be creative setting the aperture to control depth of field and setting shutter speeds to freeze action or blurring the image to exaggerate motion (use slow shutter speeds.)

THE SHUTTER

The Camera has a device that determines the length of time film or a digital sensor is exposed to light, this device is called the Shutter.
Some shutters are built into the lens, some are built into the Camera body, in front of the Film Plane (Film cameras) or light sensitive electronic sensor (Digital cameras), all are activated by depressing the shutter release button, Shutter speeds can be as slow as 30 sec. and as fast as 1/4000 sec.