In photography, “depth of field” (DOF) is the depth of the sharp area in the image, both in front of and behind the main subject of the image, the subject on which the focus was made.
Here is a diagram illustrating the concept:
Click to enlarge: Diagram illustrating the effect of the diaphragm’s aperture size, left, on the depth of field. © Charles Martel 2015
One (or two) picture is worth a thousand words, here are examples of depth of field:
Telephoto (zoom) Image with low depth of field: The picture’s background, behind the main subject, is completely blurred:
Click to enlarge: Butterfly with Shallow DOF. © Charles Martel 2015
Wide-angle image with large depth of field: The image’s foreground, center and background are in focus:
Click to enlarge: Lake, Montreal Botanical Garden, © Charles Martel 2015
Factors governing DOF:
The depth of field of an image depends on many factors, the main ones being:
The lens aperture
The larger the lens aperture, the shallower (smaller) the depth of field.
The len’s focal length
The longer the focal length, the shallower (smaller) the depth of field.
The focusing distance
The greater the distance of focus, the greater (deeper) the depth of field.
The size of the sensor
The larger the sensor, the shallower (smaller) the depth of field.
It is the combination of these factors that determines the final depth of field.
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© Charles Martel 2015