1. Topic 4: Lenses and Vision

2. Essential Learning Outcome
I can explain the use of concave and convex lenses in objects such as microscopes, eye glasses, cameras, binoculars and telescopes.

3. Types of Lenses
Lens – a curved piece of transparent material such as glass or plastic
Concave lens - thinner and flatter in the middle than around the edges causes light to spread out, or diverge
Convex lens - thicker in the middle than around the edges causes light to come together, or converge sometimes cause images to be inverted (upside-down)

4. A double concave lens is thinner and flatter in the middle than the edges. 
Light passing through the thicker more curved areas of the lens will bend more than light passing through the thinner areas, causing the light to spread out or diverge.

5. A double convex lens is thicker in the middle than around the edges. 
This causes the light to come together at a focal point, or converge.

6. Lenses and Mirrors
Lenses are useful optical devices.  Eyeglasses, have been made from lenses since the thirteenth century. 
A convex lens refracts the light rays from an object so they can be focused. 
Different size lenses can converge the light rays at different distances, enabling corrections to be made to focal points.

7. Image Projection
light from the left portion of the object is directed to the right and the light from the top is directed to the bottom.  This inverts the image.  Overhead projectors and film projectors do this

8. http://www. sumanasinc

9. Human Eye
The lens in the human eye is a convex lens. It takes light rays and focuses them on the retina, which allows us to see images.
Far-sighted vision (short eye)
image falls behind retina
trouble seeing near objects
corrected with convex lens
Near-sighted vision (long eye)
image falls short of retina
trouble seeing distant objects
corrected with concave lens

11. Nearsighted eye cannot focus on objects far away (further than the far point < infinity) If their eye is too long, the image forms in front of the retina - this is a condition called Myopic, or near-sightedness

12. Correcting Nearsightedness
Nearsighted vision can be corrected by using a diverging lens ( making the light less convergent).

13. Farsighted eye cannot focus on an object at the near point of a normal eye. If their eye is too short, the image forms behind the retina, making object that are close to them difficult to see.  This condition is called far-sightedness.

14. Correcting Farsightedness
The light is made to converge more by using a
converging lens.

16. http://webphysics. davidson

17. Image focuses ____ the retina Light must _____ to reach the retina
Short eyeball
Long eyeball
?-sighted
Image focuses ____ the retina
Light must _____ to reach the retina
Eyeglass lens used?
Far-sighted
Near-sighted
In front
behind
Converge
Diverge
Convex
Concave

19. Eye The human eye controls the amount of light using:
the iris functions like a diaphragm in dim light, the iris increases the size of the eye’s opening (the pupil)
Iris reflex – the natural adjustment in the size of the pupil
The eye is focused by changing
the flatness of the lens, in a process called accommodation.

20. Comparing the Eye and the Camera
A camera controls the amount of light using:
diaphragm controls the aperture (the opening) of a lens or optical system
a shutter limits the passage of light
The human eye controls the amount of light using:
iris functions like a diaphragm in dim light,
the iris increases the size of the eye’s opening (the pupil)
Iris reflex – the natural adjustment in the size of the pupil

21. Camera Lens refracts light
Film (or light detector) near focal point of the lens
Focusing by movement of the lens detector distance.
Aperture changes the light intensity level of the image.

22. Similarities Function Human Eye Camera
Controls amount of light entering
Iris
Shutter
Opens to the inside
Pupil
Aperture
Opens and closes to let in light
Eyelid
Diaphragm
Focus the image
Cornea & lens
Lens
Light sensitive screen that retains the image
Retina
Film

23. Differences Eye Camera Flexible eyeball Filled with fluids
Rigid camera body
Light proof box
Flexible lens
Controlled by muscles
Solid lens
Not flexible
Rods & Cones
Specialized cells which send images to brain
Silver compound in film
Retains image

24. Seeing the Image
Cells in the retina detect light and send electrical impulses to the brain through the optic nerve.
The point where the optic nerve enters the retina is called the blind spot.

25. lens - a curved piece of transparent material; light refracts as it passes through a lens, causing the light to bend
concave lens - a lens that is thinner and flatter in the middle than around the edges; causes rays to spread out or diverge
convex lens -  a lens that is thicker in the middle than around the edges; causes rays to come together or converge
retina - light sensitive area at the back of the eye; the images you see are formed on the retina
near-sighted - have trouble seeing distant objects; the eyes are too long causing the image to form in front of the retina
far-sighted - have trouble seeing near objects; the eyes are too short, causing the image to be formed behind the retina
accommodation - changing the shape of the lens to adjust for different distances of objects
near point (of the eye) - the shorter distance at which an object is in focus
far point (of the eye) -  the longest distance at which the object is in focus
diaphragm - the device that controls the aperture of a camera
aperture - the opening of camera 
shutter - limits the passage of light into the camera
iris - The colored part of the eye which helps regulate the amount of light entering the eye; it works like the diaphragm of a camera
pupil - in the eye, the colored ring that adjusts size for the amount of light available; like the aperture in the camera
iris reflex - the natural adjustment in the size of the pupils optic nerve - the nerve that connects the eye to the brain blind spot - the point where the optic nerve enters the retina; there are no light sensing cells at this point