Depth of field

Input

Focal length

f

F value

F

Circle of confusion

c

Subject distance

WD

Near depth of field

D_n

Far depth of field

D_f

Depth of field

D

Hyperfocal distance

H

An approximation that assumes the working distance is much greater than the focal length ( $WD \gg f$ ). It does not hold for macro work at or near 1:1.
The circle of confusion $c$ is the diameter up to which a blurred point still reads as a point. Around 0.03 mm is usual for 35 mm format; smaller sensors take smaller values, and two to three times the pixel pitch is another common guide.
Depth of field is not symmetrical about the subject: it reaches further behind than in front.
Focus at the hyperfocal distance $H$ and everything from $H/2$ , half of it, out to infinity falls within the depth of field. Once the working distance reaches $H$ , the far limit is at infinity, so neither the rear depth of field nor the total depth of field can be given.