The f-stop function on a camera changes the size of the camera's aperture, the opening that allows light to reach the camera's film or digital image sensor. This function allows the photographer to make an image lighter or darker.
What Does F-stop Mean?
An f-stop, or "f/stop," is the ratio of a camera's "f"ocal length divided by the diameter of its lens' aperture. The "f," the distance between lens and film, changes depending on your depth of field, or the distance from your camera that you choose to place in maximum focus.
Using an F-stop Function
Because the f-stop is a ratio, a higher f-stop number will result in a smaller aperture, less light reaching the film or sensor and a darker photograph. A lower f-stop ratio will result in a wider aperture, more light reaching the film or sensor, and a lighter photograph.
F-stop Settings
The values of f-stop numbers may appear to be a random sequence, but they have been standardized so that increasing the f-stop number by one step will halve the amount of light allowed into the camera's aperture. By the same rule, lowering your camera's f-stop by one step doubles the amount of light allowed into your camera.
Relationship to Shutter Speed Function
The shutter speed setting controls the speed at which the aperture of a camera closes. Shutter speed settings have been standardized to halve and double as they increase and decrease in the same way that f-stops have. So, for example, shutter speed can be halved as f-stop doubles to compensate for the increase in the amount of light reaching the film or sensor.
Digital Cameras
The digital cameras most commonly used by amateurs do not require as wide of a range of f-stops as manual and SLR digital cameras to achieve proper exposure. Some digital camera models use this advantage to simplify operation, which limits users' ability to modify the f-stop. Other models use settings placed in between the standard halving and doubling ratios to retain the photographer's artistic control.
