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) Converging lens (aka Convex 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.

Lens Terminology PA = principle axis F = focal point O = optical center F’ = secondary focus 2F’ or 2F = focus length from mirror x 2 PA F O F’ 2F 2F’

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 Lenses Mirrors Sensor Viewfinder Shutter BEFORE THE SHOT AFTER THE SHOT 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.

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

Which eye is your dominant eye? 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? To find out which of your eyes is dominant, form a circle with your thumb and index finger. Hold that position and place your hand in front of you. With both eyes, look at an object through the circle. Continue to hold that position and close one eye then open it. Close the other eye, open it. The eye that you could still see the object with is your dominant eye. 13

5. Movie Projector - film has images inverted so they appear upright on screen

Telescopes Lens #1 Lens #2 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.

Locating Images in Lenses Do as activity