Table 1-1. The standard sequence of whole f/number

Photographic Filters and Techniques
Page Navigation
6

Figure 1-6.

Equal f/numbers produce equal intensities

b. When photography students first encounter the f/number sequence

engraved on a lens, they are usually a little put off because it looks more

complicated than it really is. Look at the f/number sequence beginning with

f/1 in Table 1-1.

Table 1-1.

The standard sequence of whole f/number

c. The standard sequence is one which every photographer must know by

heart. Each number represents a change in the intensity of the light by a

factor of 2. As the numbers increase, the amount of light passing through

the lens decreases to half that of the previous f/number. That is, if the

lens was initially set at f/5.6 and it is changed to f/8, the light passing

through has been reduced exactly in half; and if the setting is changed from

f/8 to f/11, the light is cut in half again, and from f/11 to f/16, in half

again. The reverse happens when changing from a large f/number to the next

smaller number.

For example, a lens setting changed from f/32 to f/22

exactly doubles the intensity of the light, and from f/22 to f/16 doubles

again. Remember, as the f/number increases, the light passing through the

lens decreases because the aperture is smaller.