Lenses

• • A lens  is a transparent object with at least one curved side that causes light to refract. The shape of the lens impacts the images observed through them because of how light refracts through the lens
• Converging (convex) Lenses

  • Thickest in the middle and thinnest at the edge
  • At least one convex surface
  • Causes parallel light rays to converge (meet at a common point) at the principle focus
  • Secondary principal focuses are first
• Diverging (concave) Lenses

  • Thinnest in the middle and thickest at the edge
  • At least one concave surface
  • Causes parallel light rays to diverge (spread out) as if they had an originated from a virtual focus
  • Principal focus first
• Refracted: light ray that leaves a lens after refraction
• Principle Axis: line that goes through the optical centre of the lens and is perpendicular (90 degrees) to the centre line of the lens
• Optical Centre: centre of the lens
• Principal Focal Point: point on the principal axis of a lens where light rays run parallel to the principal axis
• Secondary Principal Focus: focus that is on the same side of the lens relative to the incident rays
• 2F’: means double the distance from the principal focus (F) to the secondary principal focus (F’)
• Converging lens

  Rule 1: a ray parallel to the principal axis is refracted through the principal focus (F)

  Rule 2: a ray through the secondary principal focus (F’) is refracted parallel to the principal axis

  Rule 3: A ray through the optical centre (O) continues straight through, without being refracted
• Diverging lens

  Rule 1: a ray parallel to the principal axis is refracted as if it had come through the principal focus (F)

  Rule 2: a ray that appears to pass through the second principal focus (F’) is refracted parallel to the principal focus

  Rule 3: a ray through the optical centre (O) continues straight through on its path