Optics for Kids - Concave vs. Convex Lenses

What Are Lenses?

What are Lenses?

Lenses bend light in useful ways. Most devices that control light have one or more lenses in them (some use only mirrors, which can do most of the same things that lenses can do).

There are TWO basic simple lens types


CONVEX or POSITIVE lenses will CONVERGE or FOCUS light and can form an IMAGE

Convex Lenses


CONCAVE or NEGATIVE lenses will DIVERGE (spread out) light rays

Concave Lens

You can have mixed lens shapes too:

mixed lens shapes

See a demonstration (opens a new window) of what happens to the light path when you combine several convex or concave lenses.

convex and concave lenses, convex vs concave, combined lenses

Perfectly straight, until something bends it. The straight paths of light are called LIGHT RAYS.

Simple or Complex Lenses?

Simple or Complex?
Simple lenses can't form very sharp images, so lens designers or optical engineers figure out how to combine the simple types to make complex lenses that work better. We use special computer programs to help us do this because it can take BILLIONS and BILLIONS of calculations.

These two devices use these types of lenses. Can you guess what they are? (Click on it to see the answer.)

lenses lenses

Magnifying Glass: A Simple Optical Device

This diagram (click it to see a bigger version) shows how a magnifying glass bends light rays to make things look bigger than they are. Many optical devices use the same basic idea of bending the light to fool your eye and brain so light LOOKS like it came from a different (usually larger or closer) object.

[Click image to see a larger image]

See a cool Flash demonstration of simple magnification from the Molecular Expressions website (opens a new window, requires a Java plug-in). Move the magnifying glass up and down.

Lenses are everywhere and have a purpose. See if you can figure out what lens is used to...

  Question Answer
1. Show a big picture on a screen?
2. See things that are far away?
3. See very small things?
4. See in the dark?
5. Capture images of things to see later?
6. Correct poor vision?

Activity Quiz

Optics in Astronomy and Space Exploration

Optics has a long history when it comes to astronomy and space exploration. Galileo (1564-1642) was one of the first to use a small telescope to look at the Moon and other objects in the night sky (the first to report his observations anyway).

He discovered...

  • That the Moon has mountain-like features
  • That Jupiter has its own moons.
  • Sunspots and that the planets were disks, not points of light like stars.

Better ground based telescopes and special optical instruments such as spectrometers enabled people to discover many secrets of the universe, and ground based telescopes and scientific optical instruments continue to be used and improved even today.

But since 1957, optics has also been an important part of the Space Age, starting with ground-based telescopes used to track rockets and satellites. Soon after there were Earth satellites with cameras, telescopes, and other optical instruments, many to look back at Earth, and many more to look at the stars and planets. A little later the US and the then Soviet Union also started to send spacecraft out of Earth orbit to visit the Moon, Venus, Mars, and eventually all the planets except Pluto (a NASA probe is on its way to Pluto now, due to arrive in 2015).

The Hubble Space Telescope is perhaps the most famous space-based optical system, and several engineers at ORA actually worked on the design and other aspects of the repair optics. We even won a NASA Public Service Group Achievement for this and other space-related work). See this diagram for how the Hubble works.