Definitions for "Stopping Down"
Changing the lens aperture to a smaller opening; for example, from f/8 to f/11. Some lenses, like PC lens or attachment with a none dedicated bellow on macro photography, stop down exposure metering is required for correct reading.
Reducing aperture size - for example, from Æ’/16 to Æ’/22.
In photography, this is the process used to decrease the size of aperture in a lens.