The depth of field (DOF) is the part of a scene with an acceptable sharpness. Although a lens can focus precisely at only one distance, the decrease in sharpness is gradual on either side of the focal length, so that within the DOF range, the imperfect sharpness is imperceptible under normal viewing conditions.

The Demonstration illustrates the fact that the DOF is much smaller in front than behind the subject and that DOF becomes more critical at smaller -numbers (larger lens openings), larger focal lengths, and at shorter subject distances.

Hyperfocal distance , near distance of acceptable sharpness , and far distance of acceptable sharpness are calculated using:

.

Drag the red lamp locator (the subject) left or right to change the focus.