1. Lenses and Our Eyes

2. Lenses convex lens – thicker in middle, thinner at edge
concave lens – thinner in middle, thicker at edge

4. Lenses
light passing through a convex lens gets closer together or CONVERGES to a single FOCAL POINT
light passing through a concave lens spreads out or DIVERGES

5. The Eye your eyes are lenses light enters through the pupil
the cornea is a protective covering over the pupil

6. the iris is a muscle around the pupil that contracts and relaxes to allow different amounts of light through
the iris is the part of your eye with colour

7. behind the pupil is the lens of your eye
its flexible like rubber
convex in shape
and small… about the size of your small fingernail
the ciliary muscles can work to slightly change the shape of the lens to help you focus
the eye is filled with vitreous humour – a liquid that keeps the eyeball from collapsing

8. Images
images come into the eye through the lens and are projected onto the retina UPSIDE DOWN
your brain then knows to process the image right side up

9. Where’s your blind spot?
complete the activity
Figure 3.37
page 217
of your text book

10. Blind Spot
when the retina senses light, small electrical impulses are produced
these impulses travel along the optic nerve from the eye to the brain
the point where the optic nerve enters the retina does not have any light-sensing cells… and this point is known as the blind spot

11. Your eye is like a camera
the aperture or opening of the camera is like the pupil of the eye
the diaphragm of the camera opens and closes the aperture like the iris of the eye
the lens focuses the image onto the film of a camera… like the lens focuses an image onto the retina of the eye

12. What happens when the lens does not focus properly?
distant objects hard to see
close objects hard to see

13. if your lens is a bit to convex it focuses images before the retina
you are near sighted and can only see things clearly if they are close up
the solution is glasses with a concave lens
if your lens is not convex enough then it focuses images farther than the retina
you are far sighted and can only see things clearly if they are far away
the solution is glasses with a convex lens

14. Test Your Vision

15. What about other eyes
dogs
dinosaurs

16. fish have rounded eyes that bulge out so they can see in practically every direction
birds have better eyesight that humans because they are sensitive to more light wavelengths
hawks can see 8 times better than us
nocturnal animals (like owls) have huge pupils to let in lots of light… so they can see at night
insects have compound eyes, with lots of lenses, so they can easily spot movement