# Spherical Lenses (continued)

### Biconcave lens

It is concave on both sides and has a thicker periphery than the central region. Notice in the picture below their elements, which are:

• • • • • • •  ### Flat-concave lens It is flat on one side and concave on the other, has a thicker periphery than the central region, its elements are:

• • • • • • ### Convex-concave lens It has one convex and one concave face, has a thicker periphery than the central region. Its elements are:

• • • • • • • ## Lens Nomenclature

To follow a pattern in lens nomenclature, it is common to use the first name of the face with the largest radius of curvature followed by the smallest radius, since the same lens may have one concave and one convex side.

## Optical behavior

As for the behavior of a beam of light when it falls on a lens, we can characterize them as divergent or convergent, depending mainly on the refractive indices of the lens and the medium. The study of convergent and divergent lenses will be seen in the next two sections.

## Optical center

For a fundamental lens study consider that the presented lens have negligible thickness compared to the radius of curvature, in this case, when representing a lens we can use only one line perpendicular to the main axis showing the lens behavior at the tips of the segment. The point where the lens representation crosses the main axis is called the optical center of the lens (O).

The representation used for the lens is:

• For converging lenses: • For divergent lenses:  