PH 103

1
PH 103

• Dr. Cecilia Vogel
• Lecture 6

2
Review

• Lenses
• ray diagrams
• images
• thin lens equation

Outline

• Lenses
• More ray diagrams
• application to camera, eye, and corrective lenses
• more thin lens equation

3
Another Ray Diagram

• Example on board
• f -25 cm, do 55 cm, di -17.2 cm, m 0.3125
• Java applet

4
View Images

• Case I converging lens, object close, forms
  image
• virtual/in front, upright, larger
• f gt0, do lt f, di lt 0, M gt 0, M gt 1 hi gt ho.
• Case II converging lens, object mid
  distance,image
• real/behind, inverted, larger
• f gt0, f lt dolt 2f, di gt 0, M lt 0, M gt 1 hi
  gt ho.
• Case III converging lens, object far forms
  image
• real/behind, inverted, smaller
• f gt0, do gt 2f, di gt 0, M lt 0, M lt 1 hi lt
  ho.
• Case IV diverging lens, forms image
• virtual/in front, upright, smaller
• f lt0, di lt 0, M gt 0, M lt 1 hi lt ho.

5
Camera and Eye

• Know image is
• behind the lens, real
• closer to lens, so mlt1, so smaller

• Must be Case III

• Therefore
• converging lens
• inverted image

6
How to focus Image

• Camera
• move lens between object and image points
• demo

• Eye
• change focal length of eye
• relaxed eye, focal length longest, view distant
  object
• tensed eye, focal length shortest, view nearby
  object

7
Vision Problems

• Near Point -- nearest distance your eye can focus
  
• Find yours
• problems if near point is gt 25 cm
• farsightedness
• Far Point -- farthest distance your eye can focus
  
• Do you know yours?
• problems if far point is lt many meters
• nearsightedness