In the study of lenses we saw that they are a set of three transparent and homogeneous media separated by two spherical surfaces, that is, non-planar surfaces. We can find spherical lenses in various equipment, such as, for example, in cameras, telescopes, telescopes and especially in glasses, used to correct any visual defect.
By definition we have seen that lenses are called convergent or divergent. We call it lens convergent the lens that makes the ray of light that falls parallel to the main axis to be directed towards a single point; and we call it lens divergent the lens that causes the light ray, when incident parallel to the main axis, to be refracted, changing its propagation direction. In the case of the diverging lens, the light rays move away from the main axis.
The study of the lens is of fundamental importance for Physics, as a spherical lens has a certain capacity to converge or diverge light rays that penetrate its surface. In physics we call this capacity vergence or convergence.
In Physics we represent the convergence of a spherical lens through the letter (V). Mathematically we define the convergence of a spherical lens as:
Where: V is the convergence of the lens and f is the focal length of the spherical lens.
We can see that the verge of a spherical lens is defined as the inverse of the focal length. As we always do for a physical quantity, the unit of measurement for the convergence of a spherical lens is m.-1, as the focal length measurement unit is given in meters (m).
The unit of measurement for the convergence of a spherical lens is also known as diopter and its symbol is di. Diopter is nothing more than the degree of a lens. Thus, according to the equation that represents the convergence of a spherical lens, we can say that the focal length of the lens is the spherical lens convergence are inversely proportional, so the longer the focal length of the lens, the greater the convergence of that lens.
By Domitiano Marques
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/fisica/convergencia-uma-lente-esferica.htm