THE PHOTOGRAPHIC EYE

For now, let's stick with the literal
kind of perspective. No matter where
you stand and where you look
(straight ahead, to one side, up or
down) objects are receding away
from you. That's how space works.
Much of the time you aren't particularly
aware of this fact.
Everything just looks normal. But
when you start drawing rectangles
around things with the frame of a
photograph, all lines become much
more obvious. The lines and angles
of the frame provide a point of
reference with which to compare
other lines within the frame. So, a
building receding into the sky above
you, or into the distance in front of
you, may seem distorted, strange or
dramatic depending on the lens
you're using.
LENSES
First let's take a look at the various
kinds of lenses available, all of which
fit into three basic categories: wideangle,
normal and telephoto.
Wide-angle lenses have a wide
angle of view. They allow a large
amount of any scene to be included
within the frame of a photograph.
They have the shortest focal lengths,
ranging from 15mm or less to 45mm.
Extreme wide-angle lenses (18mm
and below) are called "fish-eyes,"
because they produce a very distorted,
circular image. The most
common wide-angle focal lengths are
28mm and 35mm.
The next category of lenses is "normal."
These are the lenses that most
closely match the normal vision of the
human eye. They range from 45mm
to 55mm. The most common normal
lens is 50mm.
The third category is telephoto
lenses. These produce a telescopic ef-
138 The Photographic Eye
FOCAL POINT: Lenses
Long & Short
The primary factor that makes one
lens different from another is its focal
length. When a photographer speaks
of "a 50-millimeter lens," he or she
means that the focal length of the lens
measures 50 millimeters (50mm). One
millimeter is a bit smaller than 1/32
of an inch. A 50mm lens, therefore,
has a focal length of about 2 inches.
The focal length of a 200mm lens is
about 7 7/8 inches.
So, what is "focal length" and why
is it so important? Technically, focal
length is the distance from the optical
center of a lens to the film plane. This
distance is four times as long within
a 200mm lens as it is within a 50mm.
Until recently, this would have been
fairly obvious, because the 200mm
lens would have been just about four
times as long. Modern techniques of
"bouncing" (or, more precisely, reflecting)
light back and forth within
a lens, however, permit one that actually
measures less than 100mm (or
about 3 7/8 inches) to have a focal
length of 200mm.
A 50mm lens is generally considered
to be "normal" for a 35mm
camera. However, any lens with a
focal length between 45mm and
55mm falls within the normal range.
A normal lens comes nearest to the
vision of a human eye. Though you
can't see as much through the lens as
you can with your eyes, the size,
distance and proportion of what you
do see appears to be the same.
Any lens with a focal length over
55mm is in the telephoto range. Any
lens with a focal length under 45mm
is in the wide-angle range. Telephoto
lenses, then, are casually referred to
as "long" and wide-angles as "short."
Imagine that you are photographing
a house from a distance of about
50 feet. The focal length of your lens
determines how much of the house
will be recorded on the film in the
camera. With a wide-angle lens (such
as a 28mm), you would probably be
able to fit the whole house into one
frame of film. With a normal lens
(50mm) you might be able to fit in
only the front door and two windows.
With a telephoto (such as a
200mm) you might be limited to a
single window or less.
Making the lens longer reduces the
angle at which light can enter the
lens. In other words, as focal length
increases, the angle of view decreases.
(The angle of view is measured
diagonally across the image area,
from corner to corner.)
Decreasing the angle of view also
decreases the field of view. The field
.of view is what you see in the viewfinder
(and what you capture on
film). It is the image area.
With a 28mm lens, the angle of
view is 75°. The borders of the field
of view create a 75° angle (like a thick
slice of pie) that starts at your camera
and stretches out to infinity.
Anything that can be seen within that
angle will show up in your photograph.
The angle of view for a
200mm lens is only 12° (like a very
thin slice of pie). In simple terms: the
longer your lens, the less you will see
through it, and the less will appear in
your photograph. Because fewer objects
will fit into a single frame, looking
through a long lens is a little like
looking through a telescope: distant
objects appear closer, small objects
appear larger.