The relationship between depth of field and depth of focus in industrial vision lenses

We know that in industrial vision lenses, when focusing manually to capture a subject, you might notice that after achieving focus on a plane, slight adjustments of the focus ring might still yield a sharp image within a certain range. However, exceeding this range can cause the image's sharpness to decrease. This introduces two terms: depth of field (DOF) and depth of focus. Let's explore their differences.

Industrial Vision Lens

Difference between Depth of Field (DOF) and Depth of Focus

1. Different Definitions:

   • Depth of field refers to the range of distances within a scene that can produce a relatively sharp image.
   • Depth of focus is the range within which the image plane can move and still maintain a sharp image.

2. Impact of Camera Distance:

   • When the camera-to-subject distance decreases, DOF decreases, but depth of focus increases.
   • Conversely, when the camera-to-subject distance increases, DOF increases, and depth of focus decreases.

3. Impact of Magnification:

   • If the magnification of the subject increases (such as when using a long focal length lens or reducing the camera-to-subject distance), DOF decreases, but depth of focus increases.
   • If the magnification of the subject decreases (such as when using a shorter focal length lens or increasing the camera-to-subject distance), DOF increases, and depth of focus decreases.

4. Impact of Aperture:

   • Reducing the aperture size increases both DOF and depth of focus.
   • Increasing the aperture size decreases both DOF and depth of focus.

5. Impact of Sharpness Requirement:

   • Lowering the requirement for image sharpness increases both DOF and depth of focus.
   • Raising the requirement for image sharpness decreases both DOF and depth of focus.

6. Relationship to Camera Manufacturing:

   • Depth of focus is largely influenced by the construction of the camera.
   • Depth of field is mostly related to the reproduction of the subject.

These factors explain why minor adjustments in focus might still produce sharp images within a certain range and why exceeding that range leads to a loss in sharpness. It demonstrates the balance between DOF and depth of focus and how various elements influence these aspects.