1. Lenses and Vision
Topic #4

2. Types of Lenses A lens is a curved piece of transparent material
Light refracts as it passes through the lens, causing rays to bend
Lenses are generally made of plastic or glass

3. Types of Lenses (cont.)
A double concave lens is thinner and flatter in the middle than around the edges – causes light rays to diverge

4. Types of Lenses (cont.)
A double convex lens is thicker in the middle than around the edges – causes light rays to come together or converge

5. So where do we use lenses?

6. So where do we use lenses?
Eyeglasses

7. So where do we use lenses?
Eyeglasses
Overhead projectors

8. So where do we use lenses?
Eyeglasses
Overhead projectors
Movie projectors

9. So where do we use lenses?
Eyeglasses
Overhead projectors
Movie projectors
Telescopes

10. So where do we use lenses?
Eyeglasses
Overhead projectors
Movie projectors
Telescopes
Cameras

11. So where do we use lenses?
Eyeglasses
Overhead projectors
Movie projectors
Telescopes
Cameras
Microscopes

12. So where do we use lenses?
Eyeglasses
Overhead projectors
Movie projectors
Telescopes
Cameras
Microscopes
Your eyeball!!!

13. Your Eyeball The lens in the human eye is a double convex lens
It takes light rays from objects and by refraction, focuses the light at a certain point
In a normal eye, the light is focused to the back of the eyeball
on a light-sensitive area
called the retina

14. Eye Problems
Some people have eyes that are too long or lenses that aren’t properly shaped
The image forms in front of the retina
These people are near-sighted – they have problems seeing distant objects

15. Eye Problems (cont.)
Some people have eyes that are too short or lenses that aren’t working
Therefore, the image has not formed by the time it reaches the retina
These people are far-sighted – they have problems seeing close objects

16. Mr. Churchill’s problem
Astigmatism occurs when the cornea or lens (or both) are not perfectly symmetrical
Astigmatism is the loss of focus (or Refractive error) caused by this irregular shape.

17. Camera vs Eye
In your eye, your eyelids open and close to limit the amount of light reaching your eye
In a camera, the shutter does the same thing

18. Camera vs Eye
In your eye, the iris expands or contracts to limit the amount of light hitting the lens and retina
In a camera, the diaphragm does the same

19. Camera vs Eye
In your eye, the iris expands or contracts to make the pupil bigger or smaller
In a camera, the aperture is the same

20. Camera vs Eye Both in an eyeball and a camera, there is a lens
However, in some cameras, lenses can be changed or added to give you a greater magnification

21. Camera vs Eye
In your eye, the retina receives the images from the lens and then sends that to your brain via the optic nerve
In a camera, film or the image sensor captures the image from the lens. The image is either printed or sent via a memory card or cable to a computer, similar to an optic nerve