Thin Converging Lens

• Principal focus: the point where rays parallel to the principal axis converge with a converging lens.
• Focal length: distance from principle focus and the optical center.
• Principal axis: line that goes through optical center, and the 2 foci.
• Optical center: the center of the lens
• Real: image can be caught on a screen
• Virtual: image cannot be caught on a screen
• Real image: when the object is further away from the optical centre than F' is

  
  

  A) A ray through centre of the lens passes straight through the lens.

  B) A ray parallel to the principal axis passes through the focus on the other side of the lens

  C) A ray through F’ will leave the lens parallel to the principal axis

  
• Virtual Image

  • When the object is closer to the optical centre than F’ is
  • Magnifying glass: when a convex lens is used like this - an object is closer to a convex (converging) lens than the principal focus (like the diagram above), the rays never converge.

  
• With a thin converging lens, the image can be:

  • Enlarged: The image is larger than the object.
  • Same size: The image is the same size as the object.
  • Diminished: The image is smaller than the object.
  • Upright: The image is in the same vertical orientation as the object.