Thin lens
Intermediate
Converging and diverging lenses.
Converging (convex) lenses bring parallel rays to a focus; diverging (concave) lenses spread them. Their power is measured in dioptres.
A magnifying glass is a convex lens.
Thick lenses need more care.
In more detail
A thin lens is one whose thickness is negligible compared with its focal length. Converging lenses focus parallel light, while diverging lenses spread it out.
Real-world uses
- Magnifying glasses use converging lenses.
- Spectacles correct vision with thin lenses.
- Cameras, glasses and projectors all use converging or diverging lenses to form images.
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Frequently asked questions
What is the difference between convex and concave?
Convex lenses are thicker in the middle and converge light, and concave lenses are thinner and diverge it.
Are real lenses thin?
Many are thin enough that the thin lens formula gives accurate results.
How do I tell a converging lens from a diverging one?
A converging lens is thicker at the middle and brings parallel rays to a focus, while a diverging lens is thinner at the middle.
Related topics in Optics
Scattering of light · Mirage · Refraction at a spherical surface · Lens formula · Lens maker's formula · Power of a lens