A mechanical baffle, ring, or aperture placed at an image plane to sharply limit the extent of the image. It blocks off-axis rays that would otherwise cause flare or fall outside the detector's active area. Unlike an aperture stop, changing the field stop size alters how much of the scene is visible, not the brightness of the image.
Heard on the job
Insert a pinhole at the focal plane to act as a field stop and block that background scatter.
Do not mix it up with
- Aperture: An aperture stop controls image brightness and depth of focus, while a field stop controls the angular extent of the image.
Related terms
Field of view
The maximum angular or linear extent of the observable world seen through an optical system.
Aperture
A physical opening that limits the bundle of light rays passing through a system.
Field lens
A lens placed at or near an image plane to redirect peripheral rays into the next optical element.