Lenses and the human eye

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Lenses and the human eye

  1. 1. Lenses and the Human Eye
  2. 2. Types of Lenses: double convex lens single convex lens concavo-convex lens convexo-concave lens single concave lens double concave lens
  3. 3. Thin Lens Equation: d 0 = distance of object from lens d i = distance of image from lens f = focal length of the lens
  4. 4. Remember Your Signs: <ul><li>A concave lens will have a negative focal length </li></ul><ul><li>A convex lens will have a positive focal length </li></ul>
  5. 5. Remember Your Signs: <ul><li>Image distance (d i ) is positive if the image is real and negative if the image is virtual </li></ul>
  6. 7. The Eye
  7. 8. The Eye
  8. 9. Rods and Cones <ul><li>2 types of light-sensitive cells in the retina: </li></ul><ul><ul><li>120 million rod cells - act as low-light sensors </li></ul></ul><ul><ul><li>7 million cone cells - able to detect colour </li></ul></ul><ul><ul><ul><li>- 3 types of cone cells, each sensitive to one of the three primary additive colours: red , green , and blue </li></ul></ul></ul>
  9. 11. contracted pupil dilated pupil
  10. 12. How the Eye Works <ul><li>By changing the shape of the lens , a healthy eye is able to keep close objects in focus . </li></ul><ul><li>Light rays from distant objects enter the eye parallel to one another; those from close objects diverge . </li></ul>
  11. 14. Video: How the Human Eye Works http://www.youtube.com/watch?v=JadaWSDxBYk
  12. 15. Vision Problem: Myopia A nearsighted (myopic) eye focuses the light rays to a point in front of the retina Myopia can be corrected with diverging lenses
  13. 16. Vision Problem: Hyperopia A farsighted (hyperopic) eye focuses the light rays to a point behind the retina Hyperopia can be corrected with converging lenses
  14. 17. Vision Problem: Astigmatism Astigmatism is a vision problem that results from a cornea that has an irregular shape
  15. 18. Video: Laser Eye Surgery http://www.youtube.com/watch?v=0V4I2xzwGd4
  16. 19. Optical Technology Read p. 487-489 Answer questions 1-5

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