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Understanding Depth Of Field
Understanding depth of field and how it affects your photographs
In addition to its affect on exposure, the aperture setting also determines an image's
depth of field. Depth of field refers to how much of a photo will be in
sharp focus. For example, a shallow depth of field can show a person or object
in the foreground in sharp focus with everything in the background out of focus.
This draws attention to the primary focal point in the scene. A shallow depth of
field is often used in taking portraits.
A deep depth of field results in an image that is completely in focus, including
everything in the foreground and the background. An example of when you would
probably want to use a deep depth of field is when you're taking a landscape
picture.
The following picture was taken at f22. Notice how the tree branches in the
background are in focus, making it difficult to focus your attention on the
lantern.
Now let's take a look at the same picture taken at f5 (a larger aperture). Notice how the blurring
of the background draws your attention to the lantern.
The depth of field is controlled by the aperture setting. The smaller the
aperture (the higher the f-stop number) the deeper the depth of field. The
larger the aperture (the lower the f-stop number), the shallower the depth of
field.
It is important to remember that aperture and f-stop numbers have an inverse
relationship - the higher the f-stop the smaller the aperture and vice-versa.
For example, f24 is a smaller aperture than f7.
Shutter speed and aperture can be set in combinations that allow for proper
exposure under varying conditions. For example, fast action scenes like a hockey
game require a fast shutter speed to prevent blurring in conjunction with an
aperture setting large enough to ensure a proper exposure.
Most digital cameras have a programmed "sports" setting that adjusts these
settings for you, but for more control over the photo you can set them yourself
manually using the appropriate
picture-taking modes.
If the situation requires you to choose the depth of field, you can place the
camera in aperture priority mode and the camera will select the proper
shutter speed for a good exposure.
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"Digital Photography Primer"
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