Glossary · Machine vision
Depth of field
Also known as: DOF (optics), Depth of focus
German: Schärfentiefe
In optics and machine vision, depth of field is the range of object distances within which the image is acceptably sharp for the task. It increases with a smaller aperture (higher f-number), a longer working distance and a larger acceptable blur.
- Machine vision
In one sentence
Depth of field is the distance range in which the image is sharp enough; it grows with smaller aperture and longer working distance.
Example
Closing the aperture from f/4 to f/8 doubled the depth of field so that labels on both flat and curved packages stay readable.
How it applies
- Engineering: A larger f-number increases depth of field but reduces light, requiring longer Exposure time or more light, and at high f-numbers diffraction limits sharpness.
- Commissioning: Focus and aperture are set for the actual range of part heights and positions; lenses with locking screws keep the settings from shifting.
- Documentation: The documentation team should record aperture and focus settings and state the height tolerance within which the inspection works, so that product changes outside that range are recognized.
Depth of field vs. depth of focus
Depth of field is on the object side: how far the object can move and stay sharp. Depth of focus is on the sensor side: how far the sensor can move relative to the lens. The terms are often confused.