lenses

• all lenses refract light
• The light ray bends towards the normal when it passes into the lens and then away from the normal when it passes out of the lens

  
• The diagram below shows parallel rays of light passing through a convex lens. The central ray passes through the lens without being refracted. Because the ray is passing directly along the normal, it is said that this ray is passing along the principal axis (the centre of the lens). All of the other rays refract and are focused on a point (the principal focus)