1. PH 103 Dr. Cecilia Vogel Lecture 7

2. Review Outline  Lenses  ray diagrams  images  thin lens equation  Lenses  application to camera, eye, and corrective lenses  more thin lens equation

3. Camera and Eye  Know image is:  behind the lens, real  closer to lens, so |m|<1, so smaller  Therefore:  converging lens  inverted image  real image, so must be Case I

4.  Eye:  change focal length of eye  relaxed eye, focal length longest, view distant object  tensed eye, focal length shortest, view nearby object  Camera:  move lens between object and image points  like lab, demos How to focus Image

5. Vision Problems  Near Point -- nearest distance your eye can focus clearly  Find yours  problems if near point is > about 25 cm  farsightedness or hyperopia  Far Point -- farthest distance your eye can focus clearly  Do you know yours?  problems if far point is < many meters  nearsightedness or myopia

6. Correcting Nearsightedness Want: Object far away to have an image at farpoint  Know image corrective lens makes is:  upright!  closer, so smaller  Must be Case III  Therefore:  diverging lens  image is virtual, in front  image is indeed on the side of lens that the light comes from

7. Correcting Nearsightedness Use lens equation with  d o = very large # - x  1/d o = 0 approx  d i = - (far point - x)  negative d i, because virtual!  ex: farpoint = 2m, glasses 2 cm from eye x Far point Very far

8. Correcting Farsightedness Want: Object at 25 cm (comfortable for reading, etc) to have an image at nearpoint  Know image is:  upright  farther from lens, therefore bigger  Must be Case II  Therefore:  converging lens  image in front, virtual  image is indeed on the side of lens that the light comes from

9. Correcting Farsightedness Use lens equation with  d o = 25 cm - x  d i = - (near point - x)  negative image distance, because virtual! x 25 cm Near point Example: glasses 2cm from eye, near point is 45cm