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Image formation - Thin lenses

Thin converging and diverging lenses

1) What is a thin lens ?

A lens is made ​​of a transparent material (glass or plastic)
A lens always has two sides, with at least one of them that is not flat.
Lenses are present in most of optical devices such as telescopes, microscopes, camera lenses, binoculars etc..
Some lenses are called "thin" when their thickness is much less than their diameter.

2) Differences between converging and diverging lenses

There are two kind of lenses: converging lenses and diverging lenses.
- A converging lens is wider at its middle than at its edges: it is convex
- A diverging lens is thinner at its middle than at its edges: it is concave

3) Characteristics of converging and diverging lenses

Each lens owns an axis of symetry called principal axis.
The point that belongs to the principal axis and to the center of the lens is denoted by O and called optical center.

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