Saturday, May 6, 2017

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Three Factors That Affect Depth of Field

There is only one plane of focus in any photograph. On either side of this plane, the image becomes less and less sharp. The depth-of-field effect refers to the apparent distance in which details appear sharp both in front of and behind the plane of focus. This apparent distance can be long or short, depending on how the photographer manipulates a photographic system.

Aperture Selection

    The size of the f-stop has the greatest effect on depth of field in a photograph. Simply, the wider the aperture, the shorter the depth of field. Using a wide aperture such as f1.4 or f2.8 gives a shallow depth of field. A narrow opening such as f16 or f22 has a much wider depth of field, where all other factors remain constant.

Distance to Subject

    The depth-of-field effect extends approximately 1/3 of its distance in front of the plane of focus and 2/3 behind. When a subject is close to the lens, shooting a flower, for example, the total distance of the depth-of-field effect may be only a few inches, while focusing on a mountain in a landscape the depth may be miles, even if both photos were taken using the same aperture.

Degree of Enlargement

    Points in a photograph become what are called "circles of confusion," increasingly larger as subjects move away from the plane of focus. Depth of field defines at what size these circles of confusion become visible to the eye, and that is the point where depth of field ends. This is why a photograph in a 4-inch x 6-inch size looks sharp, but is less sharp when enlarged to an 8-inch x 10-inch print. In digital photography, circles of confusion become more obvious with fewer pixels per inch in a print.

Viewing Distance

    This is related to degree of enlargement. When printing photographs, the photo itself is evaluated at arm's length, yet when framed and mounted on a wall, over a couch for instance, the viewer may be at two or three times that distance. Therefore, circles of confusion that are distinguishable at one viewing distance may not be at a longer distance. A rule of thumb for optimal viewing distance for a print is twice the longest side of the print. A 4-inch x 6-inch print then prefers 1 foot and an 8-inch x 10-inch is best viewed at 20 inches, or about 2 feet.


Three Factors That Affect Depth of Field

There is only one plane of focus in any photograph. On either side of this plane, the image becomes less and less sharp. The depth-of-field effect refers to the apparent distance in which details appear sharp both in front of and behind the plane of focus. This apparent distance can be long or short, depending on how the photographer manipulates a photographic system.

Aperture Selection

    The size of the f-stop has the greatest effect on depth of field in a photograph. Simply, the wider the aperture, the shorter the depth of field. Using a wide aperture such as f1.4 or f2.8 gives a shallow depth of field. A narrow opening such as f16 or f22 has a much wider depth of field, where all other factors remain constant.

Distance to Subject

    The depth-of-field effect extends approximately 1/3 of its distance in front of the plane of focus and 2/3 behind. When a subject is close to the lens, shooting a flower, for example, the total distance of the depth-of-field effect may be only a few inches, while focusing on a mountain in a landscape the depth may be miles, even if both photos were taken using the same aperture.

Degree of Enlargement

    Points in a photograph become what are called "circles of confusion," increasingly larger as subjects move away from the plane of focus. Depth of field defines at what size these circles of confusion become visible to the eye, and that is the point where depth of field ends. This is why a photograph in a 4-inch x 6-inch size looks sharp, but is less sharp when enlarged to an 8-inch x 10-inch print. In digital photography, circles of confusion become more obvious with fewer pixels per inch in a print.

Viewing Distance

    This is related to degree of enlargement. When printing photographs, the photo itself is evaluated at arm's length, yet when framed and mounted on a wall, over a couch for instance, the viewer may be at two or three times that distance. Therefore, circles of confusion that are distinguishable at one viewing distance may not be at a longer distance. A rule of thumb for optimal viewing distance for a print is twice the longest side of the print. A 4-inch x 6-inch print then prefers 1 foot and an 8-inch x 10-inch is best viewed at 20 inches, or about 2 feet.



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