Lenses

1. Physics 139 - Physics for Optometrists Lenses • Lenses have a different optical density to the atmosphere. • Due to this and the shape of the lens, light is converged/diverged to/from a point.

2. Physics 139 - Physics for Optometrists Types of Lenses • Lenses have two surfaces off which to refract. • The combination of both surfaces causes light to either converge or diverge Converging Diverging

3. Physics 139 - Physics for Optometrists Lens Geometry Lens Plane Lens Centre Optical Axis Focal Point Focal Plane

4. Physics 139 - Physics for Optometrists Lenses • Lenses have a different optical density to the atmosphere. • Due to this and the shape of the lens, light is converged/diverged to/from a point. Optical Axis f > 0 Converging Lens

5. Physics 139 - Physics for Optometrists Lenses Optical Axis F < 0 Diverging Lens

6. Physics 139 - Physics for Optometrists Lens

7. Physics 139 - Physics for Optometrists Thin Lenses • When f >> thickness we can make some assumptions • There is just one refracting surface located at the lens plane • The combined refraction of both surfaces is created at the lens plane

8. Physics 139 - Physics for Optometrists Image Formation • Consider a convex thin lens. Optical Axis

9. Physics 139 - Physics for Optometrists Image Formation • Consider a convex thin lens. Optical Axis

10. Physics 139 - Physics for Optometrists Image Formation • Consider a convex thin lens. Optical Axis

11. Physics 139 - Physics for Optometrists Image Formation

12. Physics 139 - Physics for Optometrists Diverging Lens Optical Axis

13. Physics 139 - Physics for Optometrists Diverging Lens Optical Axis

14. Physics 139 - Physics for Optometrists Diverging Lens Optical Axis

15. Physics 139 - Physics for Optometrists Image Formation

16. Physics 139 - Physics for Optometrists Image Formation Overview • Images are formed by Mirrors and Lenses • Image positions?

17. Physics 139 - Physics for Optometrists Imaging Equations - Lenses • Imaging equations for lenses are the same as those for mirrors:

18. Physics 139 - Physics for Optometrists Images: Question • A movie camera with a lens of focal length 75 mm takes a picture of a 180 cm high person standing 27 m away. What is the height of the image of the person on the film?

19. Physics 139 - Physics for Optometrists Images: Question • An illuminated object is placed 44 cm from a screen. How far from the object should a lens of focal length 11 cm be placed in order to form an image of the screen? 22 cm

20. Physics 139 - Physics for Optometrists Images: Question • An image is formed ¾ times from a lens as compared to the distance of the object from the lens 1. • When lens 1 is replaced by lens 2 with focal length 4 cm, a real image is formed 5.33 cm away from the lens. • Completely characterize lens 1.

21. Physics 139 - Physics for Optometrists Power of a Lens • The Power of the lens is measured by the amount of convergence/divergence it creates. • Therefore it is inversely proportional to the magnitude of the focal length. • What does this mean about the shape of the lens? (Unit: diopter)

22. Physics 139 - Physics for Optometrists Problem: Lenses • Using lens has a power, P = -0.75 diopter we need to create an image 30 cm away from the lens. • Describe the shape of the lens. • What type of image will be formed? • Where should the object be placed? • What is the magnification of the image?