- A lens is any piece of transparent material with at least one curved surface.
- There are two types of lenses.
- A converging lens is any piece of transparent material that will converge parallel rays of light down to a point.
- Converging lenses are thicker in the middle than at the edges.
- A diverging lens is any piece of transparent material that will cause parallel rays of light to appear to diverge from a point.
- Diverging lenses are thicker at the edges than in the middle.
- The focal point or focus isthe point which rays of light initially parallel converge towards after emerging from a converging lens or diverge from after emerging from a diverging lens.
- In diagrams, the focus is indicated with the symbol F.
- The magnification formula.
- The thin lens formula (physicist form).
- The thin lens formula (optometrist form).
Sign conventions in geometric optics