Digital Camera Exposure
The key to really great photographs, digital camera exposure refers to the amount of light that reaches the camera's sensor. If a photograph is over-exposed it means too much light got in, and if it is under-exposed, not enough light got it. So you need to learn how you can control your digital camera exposure to be sure that you let in just enough light. Unfortunately fully automatic cameras do not allow you to manually control this factor, but more expensive cameras do provide ways that you can control digital camera exposure.
Digital Camera Exposure is controlled by three elements:
• The speed of the shutter when you shoot the photograph.
• How open the lens aperture is when you take the shot.
• The camera's sensitivity to light.
The shutter is like a small screen, usually made of metal, that is inside the lens, and that opens and shuts to allow light to enter and expose the sensor. A fast shutter speed will allow just a little light to enter, and a slow shutter speed will let much more light in. Remember that if too much light gets in, the scene or subject will be over-exposed.
The aperture is a small, adjustable opening in a kind of diaphragm in the camera-body that opens to allow the light to get past the shutter, so that it can reach the sensor. Each position has an F-number (or F-stop) and the smaller the F-number, the larger the aperture. The aperture setting not only affects exposure, but also the depth of field of a photograph. A lot of light will reduce the depth of field.
If you have a high-end or single lens reflex (SLR) model with manual controls, you will be able to control and adjust exposure. For example, if you use a fast shutter speed with a large aperture, you can freeze movement. If you use a slow shutter speed and a small aperture, you can effectively blur movement. But if you don't have manual controls, the only way to adjust this is to use what is known as the exposure compensation or EV setting. Whatthis does is over-ride the automatic controls and so enable you to lighten or darken images, which is exactly what you would do if you adjusted the F-stops.
Sensitivity is expressed as an ISO number which has been determined by the International Standards Organisation (ISO). The original rating was to determine the speed or sensitivity of film, but now there is also a similar scale for digital photographic sensitivity. There was also an older American Standards Association (ASA) rating that was what was usually printed on film boxes, so that photographers knew which setting to use when shooting.
Generally, the higher the ISO number, the more sensitive to light the camera becomes. So if you shoot outdoors in bright sunlight, you will use a low ISO 100 setting. But if you are shooting in low light, or shooting moving objects, then you will use an ISO 800 or even an ISO 1000 setting.
So you should now be able to see how all three elements affect digital camera exposure.