Exposure

Exposure is the total amount of light allowed to fall on the photographic medium (photographic film or image sensor) during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance. A camera uses two things to control the amount of incoming light (exposure):

A. Shutter:
In a camera, the shutter blocks all light from exposing the film UNTIL you press the button.Then it quickly opens and closes, giving the film a brief flash of light. You can control the length of time the shutter remains open by setting the SHUTTER SPEED.

Examples:
- A half second exposure is ONE STOP darker than a one second exposure.
- A 1/125 exposure is TWO STOPS brighter than a 1/500 exposure.
- A 1/1000 exposure is THREE STOPS darker than a 1/125 exposure.
- The longer exposures ( like 1 second ) give much MORE light to the film than a 1/1000 of a second exposure. So even though the number may look bigger, don't be deceived!

B. Aperture:
When light passes through a camera's lens, it must pass through an opening called an "Aperture". In plain english it's a hole that lets in more light when it's wide open and less when it's small. Figures, huh? In essence the aperture is just like the pupil in the human eye. You can control the aperture by setting the "Aperture Opening", also known as an F-Stop. To control how much light is passed through the lens.
Examples :
- f/4 is wider than f/16
- f/32 is narrower than f/8