Figure 1-10.Controlling polarized light.
when a section of line is secured at one end and the free
end is held in your hand and given a shake, a wave
travels down the length of the line from the end that was
shaken to the secured end just like an oscillator. A light
source acts as an oscillator. The wave motion in the line,
however, does not represent the true wave motion of
light because light waves move in all possible directions
at right angles to their direction of travel. A much clearer
picture of light wave motion can be seen by having a
number of parallel lines with each one being shaken in
a different direction-one up and down, one sideways,
and the others at various angles in between.
Ordinarily, light waves vibrate in all directions at
right angles to their direction of travel. However, when
light waves strike a series of parallel microscopic slots,
all the light that passes through vibrates in one direction.
This is polarized light. Filters that polarize light, termed
polarizing filters, have a practical use in photography
Specular reflected light, from a nonmetallic surface
at any angle between 32° and 37°, is polarized in such a
manner that the light rays vibrate in a direction parallel
to the reflecting surface. Light reflected in this manner
is said to be plane polarized and is seen as glare (fig.
1-11). There is no polarization whatsoever produced by
reflections from metallic surfaces.
In the beginning of photography, daylight, or
sunlight, was the only light source suitable for exposing
the slow film available at that time. Today, photographic
film is not only vastly more sensitive to light, but a wide
range of light sources have been developed for the needs
of the photographer. These light sources include the
following: tungsten lamps, tungsten-halogen lamps,
fluorescent lamps, and electronic flash.
Sunlight, of course, is the light photographers are
most familiar with and for good reason. It is the light
they use the most. Naturally, sunlight is the only
practical light source for general outdoor photography.
Artificial light sources, however, can provide useful
supplementary lighting to sunlight as fill-in for shadows
(to make them lighter) and take the place of sunlight
entirely for photography of small areas and close-ups.
Sunlight is often referred to as daylight. The term
daylight, as used in photography, is meant to include all
Figure 1-11.Light, plane polarized by reflection.