The fact that light refracts can be used to create a lens. Glass can be used to make images which can be magnified- either smaller or larger depending on the use case.
The two classic lens types are converging and diverging lenses.
| Converging | Diverging |
|---|---|
| Light bends towards axis | Light bends away from Axis |
| Can produce real or virtual images | Produces only virtual images |
The surface shape of most lenses resembles a section of a sphere. A thin lens has two main characteristics:
- its thickness is negligible compared to its radius of curvature
- its overall size is negligible compared to its radius of curvature
These properties are conducive to a sharp image, since the rays converge better. The shape is also easier to geometrically analyse.
You can easily show that if the second side is curved, the relationship becomes:
Where ( R_1 ) is for the surface toward the object, and ( R_2 ) the opposite side.
We define ( R ) to be positive if it is convex toward the object, and negative if it is concave toward the object. For a converging lens, ( f ) is positive, and for a diverging lens, ( f ) is negative.