In photography, a stop refers to the setting of an aperture on a camera or enlarging lens that controls the amount of light reaching the film or digital sensor. Each stop either doubles or halves the amount of light compared to the previous setting, allowing photographers to adjust exposure precisely. Stops are commonly represented by f-numbers (such as f/2.8, f/4, f/5.6), where smaller numbers indicate a larger aperture and more light, and larger numbers indicate a smaller aperture and less light.
Understanding stops is crucial for managing exposure, depth of field, and motion blur. Adjusting the aperture by one stop affects not only brightness but also the sharpness and background separation in an image. In both camera and darkroom work, the concept of stops provides a standardised way to measure and control light, making it a fundamental principle of photography.