Exposure Controls
When you take a picture, you "expose" a film or sensor to light. The two parts which work together to control your exposure are the APERTURE and SHUTTER.
Some "Point and Shoot" cameras select these automatically, but more
expensive digital cameras enable you to set these manually, or to "program" them for certain shooting conditions.
APERTURE
The aperture is an opening that changes in size to admit more
or less light (similar to the iris of an eye).
The numbers on the aperture control
are called F-stops and referred to as F16, F11, F8, and so on.
- Here's how it works:
- The larger the F-stop
number, the smaller the opening.
- Each number higher lets in half as much light as one number lower.
For example, F5.6 admits twice as much light as F8,
while F11 lets in only half as much.
The aperture doesn't work alone, however.
The shutter speed is
responsible for exposure, too. It controls
the amount of time light is allowed to reach the film or sensor.
SHUTTER
The shutter is a device that opens and closes at varying speeds to determine
the amount of time the light entering the aperture is allowed
to reach the film or sensor.
Shutter speed
is measured in fractions of a second. 125
means 1/125 of a second, 60 means 1/60. Typical shutter
speeds range from 1 second to 1/1000. A shutter speed
setting for a bright, sunny day - using an aperture
of F11 - might be 1/125 second. A cloudy day might
use 1/60 second with the same aperture, exposing the
film or sensor to light for a longer period of time.
The settings for a good exposure are determined
by a light meter. (Most 35mm cameras
have a built-in light meter that shows you the appropriate
settings, or automatically controls them.)
Aperture and shutter settings work together.
Because the shutter (like the aperture)
approximately halves or doubles the light reaching
the film or sensor with each change in setting, a number of
different combinations of settings can result in
the same exposure.
| Aperture | F22 |
F16 |
F11 |
F8 |
F5.6 |
|---|
| Shutter | 1/30 |
1/60 |
1/125 |
1/250 |
1/500 |
|---|
|
Any of the combinations shown above would result in
approximately the same exposure. |
