Also known as the diaphragm or lens opening. The aperture controls the amount of light allowed onto the film. It also influences the depth of field . This is a very important factor to keep in mind and is therefore discussed separately.

A camera is equiped with a setting mechanism to control the size of the aperture. (On instant cameras the lens opening and shutter speed are fixed.)

The aperture is also reffered to as the F-stop or F-number. The F-stop indicates how many times the diameter of the lens opening can by divided into the focal length. In short this means that a smaller lens opening will have a higher F-number. If the photographer want to allow less light into the camera he must use a higher F-number. A higher F-numer (smaller aperture) will increase the depth of field.

A setting on the F-stop ring is also known as a STOP. Each stop allows exactly half or double the amount of light onto the film, depending on the side to which the setting is changed.

On automatic cameras the aperture can be set automatically according to the prevailing light conditions. This will then be dependent on the light conditions, the shutter speed setting and other settings available on the camera. For our purposes we will only look at the effect of the aperture setting, while the shutter speed is fixed.

The first photo shows the picture taken at optimum exposure settings. The second was taken with a smaller aperture(larger F-stop value). The third photograph was taken with a larger aperture (smaller F-stop value).

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