In order to get technically good results
from photography, one must expose it correctly. An overexposed picture
will be too light and an underexposed one too dark.
The aperture is designated by f/ stops.
The standard f numbers are: f/1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22,
32, 45, and 64. Each increase in the f number reduces the size of the
aperture, halving the amount of light passing through (i.e., an
aperture of f/4 will allow through half the amount of light as f/2.8
and twice as much as f/5.6).
The shutter speed indicates the time in
seconds, the standard times being: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60,
1/125, 1/250, 1/500, and 1/1000. Each setting is about twice as fast as
the previous one.
The shutter speed and aperture are
directly related, and various combinations of them can be used to
produce the same exposure. For example, if the lighting conditions
require an exposure of 1/125 second at f/8, but you want to stop or
freeze the motion of a moving subject, you can obtain an equivalent by
increasing the shutter speed to 1/250 second, halving the time, and
opening the lens by one stop to f/5.6, doubling the intensity of the
light. Conversely, if you wanted the greater depth of field obtained at
f/11, you would have to compensate for the light loss by exposing for
1/60 second. All three settings- 1/60 second @ f/11, 1/125 second @
f/8, and 1/250 second @ f/5.6 - would give equivalent exposures.