The f-stop number is a dimensionless series of numbers that indicates the opening of the aperture and is based on the human perception of brightness. This subjectively perceived brightness
is according to a logarithmic function. The normalized aperture series consists of the numbers 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 and 32 and is derived from the ratio of the focal length of a lens to its effective aperture. Between two f-numbers or f-values, there is always the ratio root 2. The first value is the quotient of root 1, i.e. 1. The second value is that of root 2, i.e. 1.4. The third value is that of root 4, i.e. 2, and so on. A small f-number means a large aperture, a large f-number means a small aperture. Large apertures mean shallow depth of field, small apertures mean large depth of field.