It is a transparent body with two spherical faces or a spherical face and a flat face.
There are two types of lenses: converging and diverging. Quite simply, it is possible to differentiate spherical lenses: just make light rays focus on them and check the direction taken by them. Therefore, the lens will be divergent when the refracted rays diverge; and convergent, when the rays converge to a single point.
Optical center of a spherical lens
It is possible to find different lenses in our daily lives, such as those used in eye correction glasses and those found inside supermarkets or public transport buses. In both cases they have specific purposes. It is possible to verify in a lens that its vertices are in places very close to each other; in biconcave lenses the vertices almost coincide.
The midpoint (O) of the segment V 1 and V 2 is called the geometric center of the lens. When we define the thin spherical lens, we impose the condition that it has negligible thickness, that is, its vertices V 1 and V 2 theoretically coincide. Consequently, the geometric center is also coincident with V 1 and V 2 .
If we make a ray of light pass through any lens through its geometric center, we will see that the river will undergo a small deflection, called lateral deflection. However, if this lens is thin (negligible thickness in relation to the radius of curvature), the lateral deviation suffered by the light ray will be so small that we will neglect it.
Therefore, we can conclude that every ray of light that falls on a thin lens, passing exactly over its optical center O (geometric center), is able to cross it without suffering any deviation.