Photo Guide Series
A how-to selection of photo
tips and digital solutions
Depth of Field
What does the term "Depth
of Field" mean?
Generally a term used to describe the zone
of acceptable sharpness in a photograph in front of and behind the subject
focused on.
The effects of different
apertures on depth of field!
Photographers use different
apertures to produce different effects and control the zone of acceptable
sharpness. A subject, as a point of focus, shot with a 35-70mm zoom lens
at an aperture of f2.8 will generally produce a photo where only the subject is
sharp and its surroundings or background are out of focus. Whereas using
the same lens at an aperture of f/22 as an example the subject and the background are
rendered quite sharp. Note: The smaller the aperture (large f-stop)
used the slower the shutter speed and greater the potential for camera shake or
blurring. To minimize camera shake use a sturdy tripod extended to two-thirds
of its height potential and a cable release. You may also want to engage
"mirror lock" if your camera has this convenience.
Factors affecting depth of
field:
-
As stated above the smaller
the aperture (Large f number) the greater the depth of field whereas the
larger the aperture (small f number) depth of field is reduced. Most
modern professional cameras are equipped with a depth of field preview
control switch. This switch allows the photographer to view the depth
of field at the chosen f-stop to determine the range or zone of
sharpness. Once you operate the depth of field review you will notice
that the viewing screen gets progressively darker as you change from a
smaller to larger f-stop. Remember that it takes time for the eye to
adjust to the dimmer view screen.
-
Distance between camera and
subject affects depth of field. The closer the camera is to the subject the
less depth of field. For example, if you are photographing a flower
inches away from the lens in order to get a close-up shot the depth of field
would be measured in terms of millimeters rather than inches. However,
if you were photographing a distant mountain range, using the same lens and
f-stop as used to photograph the flower, the depth of field would be
significantly greater.
-
The point of focus also
affect depth of field. Generally depth of field begins in an area
roughly one-third in front of the point of focus and two-thirds beyond the
point of focus.
-
The focal length of a lens
affects depth of field. The shorter the focal length of a lens the
greater the depth of field in comparison to longer focal length lens.
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