Depth of Field Math


  • DOF = depth of field This is the range of acceptable focus in the object space. Don’t confuse this with depth of focus, which is in the sensor space and is fairly useless.
  • WD = working distance, from the lens principle point of the lens (usually in the lens) to the object. For our purposes this is the distance from the lens to the object.
  • f# = f number of the lens indicating aperture opening. For example f5.6. The f number is the focal length divided by the aperture size.
  • c = circle of confusion, believe it or not, this is what engineers call it. It is not a circle drawn around your chair. You can consider this the pixel size in the sensor plane.
  • F = focal length of the lens. For example, a 50mm lens

This is an approximation, but it should give you a good idea. Note that there is not a perfect definition of when something is in or out of focus.

So for example:
With a working distance of WD=2500 mm A 50mm lens with aperture set to f5.6, and a camera pixel size of 40 microns,

This DOF is large because your working distance is large and aperture is small!