Focusing

Light can be focused so that it appears to meet at a single point. Focusing is important for getting clear images in our eye or in photographs. Images that are not focused appear blurred.

The pinhole camera

A pinhole camera consists of a box or tube with a translucent screen at one end and a tiny hole (the pinhole) made in the other end. Light enters the box through the pinhole and is focused by the pinhole onto the translucent screen. The image is upside down and smaller than the object.

Light enters a box through the pinhole and is focused onto the screen, with the image upside-down and smaller than the object.A ray diagram to show focusing in a pinhole camera

The convex lens

A convex lens is made from a transparent material that bulges outwards in the middle on both sides. It can focus light so that appears to meet at a single point, called the focal point. Light is refracted as it passes into, then out of, the lens.

Light is refracted as it passes into, and then out of, the convex lens.A ray diagram to show how a convex lens can focus light

Convex lenses are found in:

  • magnifying glasses
  • spectacles for people with long-sight (who can see distant objects clearly but not nearby ones)
  • telescopes