In simple term, Depth of Field can be described as the area or 'zone' of a photograph that is in focus. The decrease in sharpness is gradual on either side of the focused area in the photograph.
Dept of Field is not fixed. There are three main factors that determines its extent. First is the lens aperture - the samller the aperture, the greater the depth of field. Hence, a wide aperture (eg:-f2) will have an inherently shallow depth of field than a small aperture (eg:- f6).
The Second factor affecting Depth of Field is the lens focal length. Wide angle lens produce an inherently greater Depth of Field than normal or telephoto lenses.
The Third factor affecting Depth of Field is the focus distance of the subject.The further away you focus the lens from the camera the greater the resulting depth of field. Therefore, a lens focused at 1m from the camera will produce a shallower depth of field than the same lens, set at the same aperture, focused at just 3m from the camera.
Exposure: 0.001 sec (1/1250)
Focal Length: 18 mm
ISO Speed: 100
Exposure Bias: -1 EV
YCbCr Positioning: Centered
Exposure Program: Aperture priority
Shutter Speed: 679936/65536
White Balance: Manual