square of the change in distance from the light to the subject. This sounds
confusing, but what it means is that if you double the distance from the light
to the subject, the amount of light on the subject will be reduced to a quar-
ter of its original intensity. As you can imagine, this has obvious implications
for exposure—but you should also keep in mind that changing the distance
betweenthelightandthesubjectwillalsoaffectthequalityofthelight,asdis-
cussed on page 33.
Exposure is critical, and that means you must know how to meter the light
properly. If possible, you should not rely on the in-camera light meter. These
built-in meters, called reflected-light meters, measure the light that comes
back to the camera from the subject. Based on this measurement, the meter
recommends an exposure setting that will produce tones that are 18-percent
gray. The problem with this is that the meter doesn’t know what the the sub-
ject is—whether it is a black box on a black background or a white egg on a
white background. Unless your subject actually is something with an 18-per-
cent gray tonality, the suggested reading won’t be accurate. This is why peo-
ple have exposure problems using the automatic feature on their camera.
(Note:Ifyoudoneedtouse thein-camera meter,youcanholdan18-percent
gray card in front of your subject, meter that, and be assured of much more
accurate results.)
A better type of meter for portraiture is the handheld incident-light meter.
This device measures the amount of light falling on the subject, so it gives an
appropriate reading that is independent of the subject’s tonality. To use this
kind of meter, stand at the subject’s position and point the hemisphere of the
meter at the camera lens. (Note:Flash meters are also incident-light meters.
These are helpful when using multiple strobes in a studio setup.)THE PHYSICS OF LIGHT 432-18.Scenes in which the tones are pri-
marily very light or very dark can trick
in-camera meters. A handheld incident
light meter will provide more accurate
results.
This is why people
have exposure
problems using the
automatic feature on
their camera.