What does the f of F2.8 mean? Take pictures of ...

The aperture stop of the lens is called f number (aperture f number or aperture f system). F2.8 is the diaphragm of an aperture with an aperture value of 2.8. The amount of light passing through the lens at each position is changed by 2 times, that is, the light passing through it is either doubled or halved. Because the light passes through the area of the effective aperture, not just its diameter, the F number itself is not doubled or halved in each gear, but varies by a multiple of 1.4(√2). The international series of f numbers are: 1, 1.4, 2, 2.8, 4, 5.6, 8, l l L, 16, 22, 32, 45, 64, 90 and so on. Each higher number is 0.4 times of 65438+ the previous number (occasionally an integer, for example, instead of l l.2), representing the proportion of light passing through half. In other words, the larger the number, the smaller the aperture, blocking twice as much light as the previous aperture. According to the principle that f numbers represent the proportional change of area rather than the diameter, they are multiplied by every other number in the series. The speed of the lens is the f number of its maximum effective diameter-that is, the aperture is fully open. On some lenses, this number is between two f numbers in the standard sequence, because the maximum diameter of the lens is the limiting factor. In this case, the aperture number immediately marked on the lens is the closest complete F number, and the standard series begins. View original post >>