Stop down
Glossary Terms
To stop down a lens is to reduce the aperture, or increase the f-stop number - reducing the amount of light passing into the camera through by the lens.
This is done:
- to reduce the exposure (or compensate for changing to a slower shutter speed, keeping the exposure constant),
- to increase the depth-of-field, or,
- in an SLR camera, to switch from the aperture fully open (for viewing/focusing) to the taking aperture (for depth-of-field preview, metering, or taking the photo).