Larry Grayam

Depth of field (DOF) refers to that part of a photograph that appears to be in focus. It exists within a plane perpendicular to the axis of the cameras viewpoint. The photographer chooses which affect of depth of field to choose. Narrow DOF tends to separate the subject from an out of focus background, in this image notice how a line of sharpness moves through this photograph of a tray of sewing bobbins.

While greater DOF incorporates the background as an essential element in the photo. Increasing the light allowes for a stopped down aperture and a greater depth of field.

A photographer has three tools to manage the DOF, choice of lens, aperture and focal point. The focal length of a lens affects one element of the DOF available from that lens. Generally speaking the shorter the focal length of the lens, the greater the DOF. When set at the same aperture and focal point a longer lens will always have a shallower DOF then a wide angle lens will. A focus point 2 feet from the camera will have less DOF than a focus point of 10 or 100 feet. Aperture selection is the third tool. When a lens is stopped down to, let’s say f22 it will always have greater DOF then if shot wide open at f2.8.
An example of a depth of field chart illustrates the concepts of managing DOF. The cells give two distances the first is the closest distance to the camera that the subject will be in acceptable focus. The later number is the furthest distance from the camera that the subject will be in acceptable focus.

Hyperfocal distance is a focus point that will give the greatest range of DOF keeping acceptable focus only to infinity but not beyond.
Example
24mm lens aperture of f11, focused to 9’ gives a DOF of 4’4”/infinity
200mm lens aperture of f11, focused to 550’ gives a depth of field of 282’6”/infinity
So as the chart points out if you were shooting with a 200mm lens at f11 and the main subject is 290’ from the camera focusing on infinity would put the prime subject out of focus. But focusing to 550’ moves your DOF forward so the subject and background will be sharply focused.
So have fun and happy shooting-Larry

“Revisiting On Depth of Field” was featured in TUTORIALS 11/05/09