Light intensity is controlled in one of two ways: regulating the amount of light falling on the sensor or regulating its duration on the sensor. The first method, aperture, requires an adjustable circular opening, regulating the area in which light passes through the lens.
Usually this is an iris diaphragm whose opening can be varied continuously. For reproducible settings, it has indents with tactile clicks when a defined position is reached. These are marked with numbers, such as 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32, which are called f-stops.