those across the room. The amount that light falls
off as it travels can be determined by using a
mathematical equation, one that every photogra-
pher should know about. Called the Inverse
Square Law, this equation states that light drops
off in inverse proportion to the square of the dis-
tance. I know that sounds complicated, and the
natural reaction is to skip to the next section, but
if you break it down, it’s not that tough. Take, for
example, the lamp: at 5 feet the light is pretty
strong, but at 10 feet the light is much weaker —
it is actually four times weaker than at 5 feet.
The rapid falloff of light becomes important when
shooting at night and in low-light situations,
especially when using a flash or any of the tools
described in Chapter 9. For example, say you
want to take a photo of two people, where one is
5 feet from the camera and flash, and the other is
10 feet away. The amount of light that reaches
the second person is one-quarter of the light that
reaches the first person, which can cause a lot of
problems, especially if you don’t understand what
is happening to the intensity of the light. If you
understand what is happening, you can either
move the second person closer to the first person
or add a second light that is closer to the second
person.Light sources
Many times the light source can help in deter-
mining both the direction and intensity of the
light. During the day, it is pretty easy — the big-
gest and brightest light source is the sun, which
makes it easy to determine the direction of the
light, but that all changes at night. While
moonlight (which is technically the reflection
of sunlight) can be pretty bright, at night the
other light sources are easily seen, too, such as
neon signs hanging in store windows or the lights
still on in office buildings as employees work into
the evening. These different light sources createface. Knowing that the light and microphone
don’t change, I have to wait until the performer
moves so that the light striking him does not hit
the microphone first, as you can see in Figure 2-3.
ABOUT THIS PHOTO A few seconds after I took the previous
image, the performer changed his position, so the light was no longer
hitting the microphone first and creating a shadow. Taken at 1/320 sec-
ond, f/2.8, and ISO 1600.
2-3Intensity
A very important thing to know about light is
that the illumination from a light source
decreases with distance. Just think of a lamp next
to a wall in your house; the light doesn’t light up
the whole room equally, but instead the objects
closer to the light are illuminated more than