When we, as photographers, plan a shot, one of the fundamental decisions that we must make is what we want to be in sharp focus.
What we desire to be in focus can vary radically from one image to another.
For an expansive vista of the Grand Canyon, we may desire that everything from the foreground to the farthest recesses of the canyon be sharp.
For a macro shot of a flower, we may want a very narrow range of focus so that the viewers' attention is concentrated at a specific point in the image.
The issue of what is and is not in focus is referred to as depth of field (DOF).
From a practical point of view, DOF can be defined as the nearest point to the farthest point that appears sharp in an image.
So, the question now becomes, "How can we control the DOF?" Actually, there are several factors that we can control that will affect the DOF.
Aperture The camera aperture has a very large impact on DOF.
Basically, the smaller the aperture, the greater the DOF that will result.
So, if you want a large DOF, you should use a small aperture.
For a small DOF, you will need a large aperture.
Focal Length Increasing the focal length reduces the DOF.
Conversely, decreasing the focal length increases the DOF.
Thus, long lenses typically have small DOFs, and wide angle lenses have large DOFs.
This is one of the reasons that landscape photographers often use wide angle lenses.
A wide angle lens combined with a small aperture produces a very large DOF.
Distance The greater the distance from the subject, the greater the DOF that will result.
Lens Sharpness Lens sharpness has an impact on DOF.
Sharp lenses are sharper throughout the field of view.
This increases the DOF.
Sensor or Film Size Larger sensors in digital cameras or larger film in film cameras produce greater DOF.
This is because the image from a larger sensor or piece of film does not need to be enlarged as much in order to create a print.
The less an image is enlarged, the sharper it will appear.
This increases the DOF.
Print Size The general rule is the larger the print, the smaller the DOF.
This is because the print has to be enlarged more from the original size of the sensor or film in order to create a large print.
This softens the print detail and reduces the DOF.
Focusing Distance The closer you focus, the narrower the DOF.
However, when it comes to the focus distance, there is one very special focusing distance called the hyperfocal distance.
The hyperfocal distance is the shortest distance from the camera such that everything from approximately half that distance to infinity will appear sharp.
Focusing the camera at the hyperfocal distance results in the greatest DOF possible for a given combination of aperture and focal length.
There are a number of ways to determine the hyperfocal distance.
Probably the most common method is to use a DOF guide.
A DOF guide is an inexpensive, small, plastic device that allows a photographer to determine hyperfocal distances as well as other DOF parameters.
In addition, photographers that have older lenses may find that their lenses have DOF scales engraved on the lenses.
To set the hyperfocal distance, one simply aligns the infinity symbol with the color coded DOF lines.
Unfortunately, most modern lenses no longer have DOF scales.
With the above information, you should be ready to head into the field with full control over the DOF in your images.