An aperture acts as a boundary that determines exactly how much light can travel through an optical path. It can be a fixed hole in a metal plate, an adjustable iris, or simply the clear edge of a lens mount. By intentionally restricting the beam, engineers control the amount of light, block stray reflections, and dictate the depth of focus.
Stop down the aperture on the spatial filter until you see a clean diffraction pattern.
In laser labs, clipping a high-power beam on an aperture edge can cause severe diffraction ripples or even melt the metal.
Also heard as
- clear aperture
Related terms
Angular aperture
The angle subtended by the edge of an optical element as measured from the focal point.
Field stop
A physical aperture that restricts the field of view in an optical system.
Clipping
A beam partly cut off by an aperture, mount or edge, causing power loss, diffraction rings and hot spots.