THE ANGLE OF INCIDENCE IS EQUAL TO THE ANGLE OF REFLECTION
In physics, the law of reflection states that angle of in-
cidence is equal to the angle of reflection. This tenet is
fundamental to the understanding of light and can be
summarized thusly: if light strikes an object at angle A,
it will be reflected in the opposite direction, also at
angle A, similar to the way a ball bounces off a brick
wall. In photography, the law of reflection is rarely dis-
cussed; one typically hears more about the Inverse
Square Law or that white reflects and black absorbs.
While these are indeed important aspects of light, the
angle of incidence and the angle of reflection are two
components of physics that, once understood, can help
photographers improve the images they create in both
artificial and natural light.
The easiest way to comprehend this concept is to go
into a place that has hard, shiny floors and overhead
lighting (grocery stores work great!). Look down while
you walk and you’ll see hot spots of light on the floor
move with you as you walk. These hot spots are the di-
rect reflection of the overhead lighting, and they evi-
dence the law of reflection. These equal angles of
incidence and reflection can cause hot spots on your
subject too. Understanding the law of reflection will
help you avoid hot spots on your subjects, whether you
are photographing models, cars, food, or landscapes.
In fact, managing these equal angles of reflection in
your photographs allows you to add or eliminate tex-
ture and color in your images.
The law of reflection is also responsible for the red-
eye effect that plagues ring flash users when shooting
through the ring. Because the camera’s lens is at the
same angle to the subject as the flash, the reflection of
light against blood vessels in the retina at the rear of
the eye produces red-eye. An easy way to eliminate red-
eye is to brighten the room; this causes the subject’s
pupils to contract, thus greatly reducing any reflection.
Another method is to take a monolight with a 7-inch,20-degree grid and point it at your subject’s face with
only the modeling lamp powered on (not the flash unit
itself). Many flash units, including the Broncolor,
Hensel, and Profoto brands have separate switches for
the modeling lamp and electronic flashtube, allowing
them to be powered separately.
In the studio, you can use the monolight red-eye re-
duction technique described above in a darkened room.
This will allow you to show more of your subject’s iris
and less of their dark pupils. The technique works well
with light-colored eyes—especially green and blue.
Don’t be alarmed by the appearance of harsh shadows
on one side of the nose, as the power of the artificial
flash will knock this out when it fires.
The law of reflection is especially troublesome when
glass or mirrors are present in the image. The equal an-
gles of incidence and reflection cause hot spots in glass
and mirrors when using a flash. The simple solution is
to move the flash away from the camera so that the an-
gles are not identical.
By moving the camera and light source(s) independ-
ently, you can use the law of reflection in your favor, al-
most like an added layer of makeup to smooth your
subject’s skin. As you walk around your subject, you will
notice that hot and washed out spots will appear and
disappear based on the angle of reflection. You may
also notice that your model’s face appears smoother
from one angle and rougher from another angle, as the
valleys of the pores are filled in with shadows. Through
positioning your camera and light sources independ-
ently, you can eliminate hot spots and create the ap-
pearance of a smoother skin texture.
You can also use a technique often employed by Play-
boy photographer Arny Freytag—“over and under” light-
ing. Basically, in this technique, the photographer will
place the main light (usually an octabox) slightly higher
than the subject. Another light source, powered down