Focus On Lighting Photos Focus on the Fundamentals.pdf

judgment calls. They depend not
only on the subjective opinion of
the viewer but also on the size of
the reproduced image; an image
that appears sharp at a small
size may appear unsharp when
it is enlarged. The mathematical
formula for depth of field
reflects this complexity and
literally (we’re not joking here)
includes a term representing
the “circle of confusion.” For
practical purposes, depth of field
is determined by two factors:
aperture and image size. The
smaller the aperture, the greater
the depth of field; the smaller the
image size, the greater the depth
of field. Many photographers
already understand the effect of
aperture: a picture shot at, say,
f/16 will have a lot more depth
of field than the same scene shot
at f/2.8. The effect of image size
is less apparent but still easy to
understand. Many photographers
believe that wide-angle lenses
produce more depth of field.
They really don’t: they simply
produce smaller images and
smaller images have greater
depth of field. If we move the
wide-angle lens close enough to
the subject to produce the same
size image, the depth of field is
the same as that of a longer lens
from a greater distance.
Diffuse Reflection: Light
reflecting from the subject equally
in all directions, regardless of
the direction from which the
light comes. Uncoated white
paper and nonglossy white cloth
produce a great deal of diffuse
reflection. Diffuse reflection is a
property of the subject itself and
has nothing to do with whether
the light source is in any way
diffused. Compare with direct
reflection.
Diffusion: The spread of light.
The practical importance is that
diffusion turns a small light into
a large one. Photographers
use both diffusion material and
bounced light to accomplish this.
Diffusion Material: Any of
a variety of materials used to
diffuse light: tracing paper, white
cloth, or commercially produced
translucent white plastic (which
comes in a variety of densities).
Diffusion material makes little
lights into bigger light sources,
with resulting softer light.
Professionally made diffusion
material is available in both rolls
and sheets.
Direct Reflection: Direct
reflection happens in only one
direction and that direction
is the opposite of the angle
at which the light strikes it.
Examples include mirrors, bright
metal, and water. Compare with
diffuse reflection.
Distortion: Proportions not
being recorded “realistically.”
Caused by either the lens or the
camera viewpoint. Lens distortion
is sometimes a result of defects in
the lens. This is rarely noticeable
in today’s lenses, except for very
wide-angle lenses. Perspective
distortion happens with all
lenses. Dependent on camera
viewpoint: the closer the camera,
the greater the perspective
distortion. This leads many
photographers to mistakenly
believe wide-angle lenses cause
distortion. They don’t, but the
closer viewpoint they allow does
increase distortion. The effect
may be pleasing: a country road,
becoming ever smaller in the
distance. However, it may be
displeasing: a cityscape with tall
buildings on the left and right
leaning toward the center of the
picture. Displeasing perspective
distortion can be corrected
with postproduction software,
sometimes with a significant
loss of image quality; may also
be corrected without significant
loss of quality using perspective
control lenses or view cameras,
both increasingly rarely used by
current photographers.
Glossary 187