Unit C Lesson C7 The Many Uses of Lenses
Completion requirements
Lesson C7: The Many Uses of Lenses
Video Lesson
Lenses can bend light to change the size of images. For this reason, lenses are used in many optical technologies. Watch this video to learn more about the many uses of lenses.
Lesson C7: The Many Uses of Lenses
Figure C.2.7.1 – Projectors create large images of digital media.
Figure C.2.7.2– Some images from lenses can be projected on a screen.
Figure C.2.7.3– Before digital cameras, film reels of movie images were quickly rolled past a light and lens to project an image onto a screen.
Reading and Materials
for This Lesson
Science in Action 8
Reading: Pages 204–210
Materials:
Smartphone, cardboard box with flaps, magnifying glass, duct tape, pencil, utility Knife (X-Acto™ knife), scissors, white wall or screen.
Up On The Big Screen
Many people like to watch movies on the big screen because it makes the story more dramatic and exciting. Watching movies on a large theatre screen is possible because of the lenses in a movie projector. To project a large image, light from the original picture passes through a convex lens, which enlarges and projects the image onto a screen. The white screen reflects light from the image back to the viewer’s eye.
Movie projectors have changed over time. Old movie projectors used film reels. Film is a transparent plastic material that records images. Movie film reels quickly rolled between a bright light and the convex lens. Light rays travelled through the film and then the lens, producing a large real image to project on the movie screen.
Modern projectors work on the same principle of using a lens to make a large image. Instead of film, light travels through a liquid crystal display (LCD) screen of tiny pixels to create an image.
Many people like to watch movies on the big screen because it makes the story more dramatic and exciting. Watching movies on a large theatre screen is possible because of the lenses in a movie projector. To project a large image, light from the original picture passes through a convex lens, which enlarges and projects the image onto a screen. The white screen reflects light from the image back to the viewer’s eye.
Movie projectors have changed over time. Old movie projectors used film reels. Film is a transparent plastic material that records images. Movie film reels quickly rolled between a bright light and the convex lens. Light rays travelled through the film and then the lens, producing a large real image to project on the movie screen.
Modern projectors work on the same principle of using a lens to make a large image. Instead of film, light travels through a liquid crystal display (LCD) screen of tiny pixels to create an image.
Watch More
High Definition Digital Projectors
Watch this video to see how high-definition digital movie projectors work.
Watch this video to see how high-definition digital movie projectors work.
Watch this video to see how Canada’s IMAX now has laser digital projectors.
Try It!
Make a Smartphone Projector
Try this simple experiment to project images onto the wall with your smartphone.
Materials:
Try this simple experiment to project images onto the wall with your smartphone.
Materials:
- Smartphone
- Cardboard box with flaps
- Magnifying glass
- Duct tape
- Pencil
- Utility knife (X-Acto™ knife)
- Scissors
- White wall or screen
Safety Warning
This
activity must be completed with the supervision
of an adult. DO NOT attempt this activity by yourself.
Take care with sharp knives; don't cut yourself or anyone else!
Take care with sharp knives; don't cut yourself or anyone else!
Instructions:
- Place the magnifying glass on one short side of the cardboard box, near the bottom of the box. Use the pencil to trace around the circular part of the magnifying glass.
- Have an adult help you cut out the circle with the utility knife.
- Place the magnifying glass over the circular hole. Tape the edges of the magnifying glass to the cardboard box with duct tape.
- Have an adult help you cut off the flap from one short side of the box, with the utility knife.
- Fold this cardboard flap in half to form a stand for the smartphone.
- Place the folded cardboard flap in the bottom of the box, so that a flat face of the stand faces the magnifying glass. Tape the smartphone stand in place so that it can hold the smartphone upright.
- Change the smartphone’s settings so that the screen image stays fixed in a horizontal position.
- Load up a video or photo on the smartphone screen.
- Place the smartphone inside the box, on the stand, with the image upside-down.
- Close the flaps on the box and tape them shut so that light from the smartphone cannot exit the box.
- Place your projector at the opposite end of a room from a white wall or screen. Aim your projector at the wall and turn off the lights.
- Adjust the phone’s position in the box, or move the box projector closer to the wall, until you see a large, clear image.
- Watch this video to see a version of this experiment and its results:
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
The magnifying glass is a convex lens because it creates a real image that can be projected onto the wall.
Convex lenses form real images with an opposite orientation. You had to place the smartphone upside-down in the box in order to make an image appear right-side-up on the screen.
Lesson Activity
Problem:
Try this online simulation to explore how lenses form images.
Instructions:
- Click here to open the lens simulation.
- Play with the simulation to see what happens when you change different parts of the simulation. Drag the object back and forth. Drag the focus and height sliders back and forth. Click the “converging” and “diverging” buttons.
- Click on the “converging” button to use a convex lens. Move the candle to create the following situations and observe what happens to the image.
- Place the candle at 2f.
- What do you notice about the candle’s image?
- Change the height of the candle. What happens to the image?
- Drag the focus point closer and farther away from the lens. Drag the object onto 2f. What happens to the image?
- Place the candle beyond 2f. Repeat the steps in Part A.
- Place the candle between f and 2f. Repeat the steps in Part A.
- Place the candle at f, the focal point. Repeat the steps in Part A.
- Place the candle between the lens and f. Repeat the steps in Part A.
- Click on the “diverging” button to use a concave lens. Move the candle to create the same situations for the converging lens, as in Step 3.
Analysis Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
When an object is located very far away from a converging lens, the lens creates an upside-down image on the opposite side of the lens. The image is smaller than the original object, and is located between the focal point (f) and twice the focal
point (2f).
When an object is placed between twice the focal length (2f) and the lens, it forms a larger image.
An objects that is very close to a converging lens forms a larger virtual image on the same side of the lens.
A diverging lens forms smaller virtual images on the same side of lens as the object.
Figure C.2.7.4– Camera lenses focus light.
Figure C.2.7.5– Different camera lenses collect different amounts of light.
Figure C.2.7.6– Lenses that magnify far images have long focal lengths.
Camera Lenses
Different camera lenses have different focal lengths. The focal length is the distance from the camera lens to the focused image.
Camera lenses with longer focal lengths can magnify far-away objects. These are known as telephoto lenses. Some common focal lengths of telephoto lenses are 85 mm, 135 mm, or 200 mm. Lenses with longer focal lengths require longer lens barrels. That’s why telephoto lenses, like ones used to photograph wildlife, are long and heavy.
Camera lenses with shorter focal lengths can capture a large field of view to make wide-angle images. Wide-angle lenses have focal lengths of 18 mm or 35 mm and are shorter in length.
Many modern camera lenses are zoom lenses. A lens inside a zoom lens camera barrel moves back and forth, changing the focal length. As a result, a zoom lens can act like both a wide-angle and telephoto lens.
Different camera lenses have different focal lengths. The focal length is the distance from the camera lens to the focused image.
Camera lenses with longer focal lengths can magnify far-away objects. These are known as telephoto lenses. Some common focal lengths of telephoto lenses are 85 mm, 135 mm, or 200 mm. Lenses with longer focal lengths require longer lens barrels. That’s why telephoto lenses, like ones used to photograph wildlife, are long and heavy.
Camera lenses with shorter focal lengths can capture a large field of view to make wide-angle images. Wide-angle lenses have focal lengths of 18 mm or 35 mm and are shorter in length.
Many modern camera lenses are zoom lenses. A lens inside a zoom lens camera barrel moves back and forth, changing the focal length. As a result, a zoom lens can act like both a wide-angle and telephoto lens.
Figure C.2.7.7– Purple fringing up close.
Chromatic Aberration
A situation called chromatic aberration can sometimes occur on photographs. Chromatic aberration is colour fringing around the edge of objects in photographs. A faint green or purple line can be seen around the edge of an object in the photograph, which isn’t there in real life. Chromatic aberration is more likely to occur around dark objects on a light background. For example, it might occur in a picture of a person against a white wall.
Camera lenses cause chromatic aberration. Different colours of light refract slightly different amounts when passing through a lens. Purple light bends more than red light. All the coloured light rays don’t focus at exactly the same spot, which causes the appearance of a purple or green line surrounding an object.
A situation called chromatic aberration can sometimes occur on photographs. Chromatic aberration is colour fringing around the edge of objects in photographs. A faint green or purple line can be seen around the edge of an object in the photograph, which isn’t there in real life. Chromatic aberration is more likely to occur around dark objects on a light background. For example, it might occur in a picture of a person against a white wall.
Camera lenses cause chromatic aberration. Different colours of light refract slightly different amounts when passing through a lens. Purple light bends more than red light. All the coloured light rays don’t focus at exactly the same spot, which causes the appearance of a purple or green line surrounding an object.
Figure C.2.7.8– Camera lenses refract light colours at different angles, which causes chromatic aberration.
Figure C.2.7.9– Chromatic aberration is seen as purple lines around objects.
Connections
Figure C.2.7.10– Liquid lenses can be found in nature, if you know where to look.
Figure C.2.7.11– Certain liquids can be shaped by electrical currents to form lenses.
Connections – Technology
>> Liquid Lenses
One drawback to the use of lenses in optical technologies is that lenses are often made of glass, which makes them fragile. Lenses must be handled with care, or they can break and be scratched easily.
To avoid the fragility of glass lenses, some scientists are developing new liquid lenses. Electricity is used to change the shape of these lenses, to make them focus in response to an object.
>> Liquid Lenses
One drawback to the use of lenses in optical technologies is that lenses are often made of glass, which makes them fragile. Lenses must be handled with care, or they can break and be scratched easily.
To avoid the fragility of glass lenses, some scientists are developing new liquid lenses. Electricity is used to change the shape of these lenses, to make them focus in response to an object.
Figure C.2.7.12– In a process called electrowetting, an electric current is run through a droplet of a substance like mercury to form a liquid lens.
Watch More
Liquid Lenses
Watch this video to find out more about the invention of liquid lenses.
Watch this video to find out more about the invention of liquid lenses.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit C Lesson 7 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Be a Self-Check
Superhero!
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
Digital movie pictures need to be positioned close to the lens, just beyond the focal point, in order to create a large real image on the other side of the lens. This large real image can be projected on a theatre screen.
When light from a digital image passes through the projector’s convex lens, the image’s orientation is reversed. In order to make images appear right-side-up on a screen, the original image must be upside-down in the projector.
Convex lenses are able to make light rays converge into a real image on the opposite side of the lens, which can be projected on a screen. Concave lenses make light rays spread apart, or diverge, which creates a virtual image on the same side
of the lens. Virtual images can be seen by looking into the lens, but cannot be projected onto a screen.
In order to focus an image inside the telescope barrel, the lens closest to the sky must be a converging convex lens. A diverging concave lens would not work, it would spread light rays outward, and the light rays need to be directed inward.
To illuminate a large area, a concave or diverging lens should be placed in front of the light. A diverging lens will spread out light rays over a large area.