• A lens is a piece of equipment that forms an image by?refracting?light
• There are two types of lens:
  • Convex
  • Concave

   

Convex Lenses

• In a convex lens, parallel rays of light are brought to a focus by refraction
  • This point is called the?principal focus

   

• This lens is sometimes referred to as a?converging?lens
• The distance from the lens to the principal focus is called the?focal length
  • This depends on how?curved?the lens is
  • The?more?curved the lens, the?shorter?the focal length

The focal length is the distance from the lens to the principal focus

Concave Lenses

• In a concave lens, parallel rays of light are made to diverge (spread out) from a point
  • This lens is sometimes referred to as a?diverging?lens

   

• The principal focus is now the point from which the rays appear to diverge from

Parallel rays from a concave lens appear to come from the principal focus