12Concepts in PhotographyThe size of the aperture is represented by a value known as an“F-number.” The f-number represents the focal length divided by thediameter of the lens. For example, if a lens with a 50 mm focal lengthhas an f-number of F2, the diameter of the aperture is 25 mm. (50mm/25 mm=F2) The smaller the f-number, the greater the size of theaperture.The opening in the aperture is described as the Exposure Value (EV).Increasing the Exposure Value (+1 EV) means the amount of lightdoubles. Decreasing the Exposure Value (-1 EV) means the amount oflight halves. You can also use the exposure compensation feature tofine-tune the amount of light by subdividing exposure values into 1/2,1/3 EV, and so on.+1 EVF1.4 F2 F2.8 F4 F5.6 F8-1 EVExposure Value StepsAperture value and the depth of fieldYou can blur or sharpen the background of a photo by controlling theaperture. It is closely related to the depth of field (DOF), which can beexpressed as small or large.A photo with a large DOF A photo with a small DOFThe aperture housing contains several blades. These blades move togetherand control the amount of light passing through the center of the aperture.The number of blades also affects the shape of light when shooting nightscenes. If an aperture has an even number of blades, light divides into anequal number of sections. If the number of blades is odd, the number ofsections is double the number of blades.For example, an aperture with 8 blades divides light into 8 sections and anaperture with 7 blades into 14 sections.7 blades 8 blades
