Depth of Field
The range of distances in front of and behind the plane of focus that appears acceptably sharp in the final image.
Formula / rule
DoF ≈ 2u²Nc / f²
Measured in
m
In depth
Depth of field is not a physical boundary but a perceptual judgement, defined by how large a blur circle a viewer will accept. It shrinks with wider apertures, longer focal lengths and closer subjects, and it is distributed roughly one-third in front of the focus point and two-thirds behind at moderate distances — a ratio that approaches even at close range and diverges toward infinity.
Examples in practice
A 50 mm lens focused at 3 m gives about 1.6 m of depth at f/8 but only 25 cm at f/1.4.