# Lenses - PowerPoint PPT Presentation

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Lenses. Lenses are transparent objects that are used to refract light to help form an image There are two types of lenses:. Converging lens (aka Convex Lens). DO NOT COPY. Diverging lens (aka Concave Lens). Go experiment with shooting more than one

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Lenses

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### Lenses

• Lenses are transparent objects that are used to refract light to help form an image

• There are two types of lenses:

### Converging lens (aka Convex Lens)

DO NOT COPY

Diverging lens (aka Concave Lens)

Go experiment with shooting more than one

light ray through the different lenses in your

ray box kits

what does a converging lens do to light?

What does a diverging lens do to light?

What happens when you shine light through one lens, and then the other?

Which lens is like the one in your eye? Glasses?

Find the F and mark. What happens when you shoot a ray through the F? Shoot a ray parallel to PA? Shoot a ray through O?

### 1. Converging lens (aka Convex Lens)

• Thicker in the center than at edges

• causes parallel light rays to converge (come together) to a single focus point after refraction.

### 2. Diverging lens (aka Concave Lens)

• Thicker in the edges than at center

• causes parallel light rays to diverge (spread out) after refraction.

O

PA

2F’

F’

F

2F

O

PA

2F

F

F’

2F’

### Lens Terminology

PA = principle axis

F = focal point

O = optical center

F’ = secondary focus

2F’ or 2F = focus length from mirror x 2

### Light Ray Rules

• A ray shone parallel to axis is refracted through the F.

• A ray shone through F’ is refracted parallel to PA.

• A ray shone through O does not refract and goes straight through

### Locating Images in Converging Lenses:

Case 1: An object outside 2F’

Case 2: An object between 2F’ and F’

Case 3: An object on F’

Case 4: An object between F’ and Mirror

Try Worksheet – Converging lenses ONLY

### Applications of Converging Lenses:

1. Magnifying Glass

- image is enlarged

- object must be between focal length and lens

2. Camera’s

- the mirror goes up and stops reflecting image to the viewfinder.

- The shutter opens and the film or sensor is exposed to form inverted image

### Cameras

BEFORE THE SHOT

AFTER THE SHOT

Mirrors

Viewfinder

Lenses

Sensor

When the person is ready to take the photo, the mirror goes up and stops reflecting image to the viewfinder.

The shutter opens and the film or sensor is exposed – information is collected to create the negative or digital image.

Shutter

3. Eyes

- lens focus and inverts image to back of eye (retina)

- Your brain is what really flips the image.

4. Glasses

- far sighted = can’t see near because eye converges beyond retina.

- Converging lens refocuses light onto retina

• The sheep eye has 4 external attached muscles which control the eye movement. The human eye has six. The additional muscles allow humans the ability to “roll” and move their eyes in all directions.

• Although the muscles of each eye work collectively as a team, the eyes themselves do not focus or work together until months after birth. Most people have one dominant eye.

• Which eye is your dominant eye?

5. Movie Projector

- film has images inverted so they appear upright on screen

### Telescopes

• Uses two converging lens to project an upright, real image into eye.

• The first converging lens, projects image, but it is inverted.

• The second converging lens takes image and projects it as upright into the users eye.

Lens #1

Lens #2