Aperture (F) is the term that indicates the size of aperture on objective, which is directly associated with the amount of light that is going to fall on sensor. Bigger aperture brings more light in same time unit. Aperture is one of the most basic characteristics of objective, which tells us alot of it's value and purpose. Aperture is designated with number F so that smaller number matches bigger aperture size. That way, for objective that has F2.8 we say it is faster from the one that has maximum of F4, because it can catch more light in the same time unit. In this case - twice as much. F values are: 0.7, 1, 1.4, 2, 2.8, 4, 5.6, 8. 11, 16, 22, 32, 45, 64. Every next, greater value F, means that twice less light leaks through in the same time unit then previous, with smaller value F. So for example F5.6 flows through twice as much light on sensor then F8, but also twice less then F4, which again has 4 times more flow of light then F8. Not to complicate too much, here goes the conclusion: the greater the F number is, the lesser the flow is, and vice versa. Besides these real apertures that are specified, cameras also have amid aperture, which exist so we could have greater manipulation possibilities trying to determine exposition.