CHAPTER 4 THE IMPORTANCE OF LENSES 59■ If you are using a short focal-length lens, you will have more depth of field
than with a long lens.
■ If the important parts of the scene are more or less on the same plane left to
right, they are all likely to appear sharp as long as you have focused on one
of them.But when you photograph a scene up close, with a long lens, or with important
parts of the subject both near and far, you might want to increase the depth of field
so that parts of the scene in front of and behind the point on which you focused will
also be sharp (see Figure 4.13).FIGURE 4.13
Telephoto lenses
require you to
“stop down” the
lens to f/22;
otherwise, sub-
jects not in
focus will be
blurred.
Sometimes, though, you will want to blur a distracting background that draws
attention from the main subject. You can accomplish this by decreasing the depth of
field.
You can use the aperture to control depth of
field. To increase the depth of field so that more
of a scene in front of and behind your subject is
sharp, setting the lens to a small aperture is
almost always the first choice. Select f/16 or f/22,
for example, instead of f/2.8 or f/4. You might
have to use a slower shutter speed to maintain
the same exposure, however. A slow shutter
speed can be a problem if you are photograph-
ing moving objects or shooting in low light.tip
Slow shutter speeds at
small apertures usually
require a tripod. Keep a tri-
pod in the trunk of your car
for just this purpose!