Stopping down refers to the process of reducing the size of a camera lens aperture, which limits the amount of light passing through the lens to the film or sensor. This is typically done by selecting a higher f-number, such as f/8 or f/16, compared to a wider aperture like f/2.8. By decreasing the aperture size, photographers can achieve a greater depth of field, making more of the scene appear in sharp focus from foreground to background.
While stopping down improves image sharpness across the frame, it also reduces the amount of light reaching the sensor, which may require slower shutter speeds or higher ISO settings to maintain correct exposure. This technique is essential in landscape, architectural, and macro photography, where controlling focus and maintaining detail throughout the scene are critical. It also helps reduce certain lens aberrations and vignetting, contributing to cleaner, more precise images.