Aperture



One effect by altering the size of the opening is that it control the depth of field and in flash photography it controls the amount of light from the flash i contrast to the ambient light. The aperture is measured by the size of it's opening (f-stop)

The f-numbers are letting double the amount of light in for each stop The numbers are not random, f2,8 i twice of f1,4 and f5,6 is twice of 2,8, 1,2,4,8,16 follow the same path. Just remember that f2 let's twice as much light in as f1,4 and that one stop of light.

Some cameras can be adjusted to have half a stop and 1/3 a stop

Also see

 * Aperture priority