13.5
Lens Applications
OVERALL EXPECTATIONS
• evaluate the effectiveness of technological devices and procedures designed to
make use of light, and assess their social benefits
• demonstrate an understanding of various characteristics and properties of
light, particularly with respect to reflection in mirrors and reflection and
refraction in lenses
SPECIFIC EXPECTATIONS
Time
45–60 min
Other Program Resources
BLM 13.5-1 Try This: Creating
a Pinhole Camera
Science Perspectives 10
website www.nelson.com
/sciencepersectives/10
Relating Science to Technology, Society, and the Environment
• analyze a technological device that uses the properties of light, and explain
how it has enhanced society
Understanding Basic Concepts
• explain the conditions required for partial reflection/refraction and for total
internal reflection in lenses, and describe the reflection/refraction using
labelled ray diagrams
• describe the characteristics and positions of images formed by converging
lenses, with the aid of ray diagrams
• identify ways in which the properties of mirrors and lenses (both converging
and diverging) determine their use in optical instruments
Related Resources
Gizmos: Refraction;
Ray Tracing (Lenses)
Berry, Richard. Build Your
Own Telescope. Charles
Scribner and Sons, 1985.
Rogers, Kirsteen. The
Complete Book of the
Microscope. Usborn
Publishing, 2006.
Stefoff, Rebecca. The
Camera. Marshall
Cavendish, Benchmark,
2008.
KEY CONCEPTS
• Both ray diagrams and algebraic equations can be used to determine the
characteristics of an image in a lens.
• Lenses have many technological uses that benefit humans.
Science Perspectives 10
ExamView® Test Bank
EVIDENCE OF LEARNING
Science Perspectives 10
Teacher eSource SUITE
Upgrade
Science Perspectives 10
website www.nelson.com
/sciencepersectives/10
Look for evidence that students can
• explain the function of a camera, movie projector, microscope, telescope, and
magnifying glass
• explain how the lenses used in a camera, movie projector, microscope, telescope,
and magnifying glass form real and virtual images
• understand how these optical devices compensate for inverted images
• realize that a charge-coupled device has replaced film in many devices that use lenses
SCIENCE BACKGROUND
Cameras
that lets light enter. Because light
travels in straight lines, a small
inverted image of an object gets
projected on the back wall of camera
obscura as shown in the diagram on
the next page.
▼
• The first camera was a camera
obscura, built by Iraqi scientist Ibn
al-Haytham and described in his Book
of Optics. A camera obscura is simply
a darkened chamber with a pinhole
▼
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Image
Aperture
Object
Darkened Room
• People used camera obscuras to create
images by tracing the image inside
of the chamber. Some art historians
suspect that Dutch master painters
such as Johannes Vermeer actually used
a camera obscura to generate images.
• Eventually, a lens replaced the pinhole
in the camera obscura. Now a focused
image would appear on the back wall
of the chamber.
• Frenchman Joseph Niépce in 1814 used
a mixture of silver and chalk spread
over paper to capture an image.
The method worked, but the image
faded as the silver-chalk mixture
continued to darken with time. Later,
Niépce used a pewter plate coated with
bitumen in his chamber. The bitumen
hardened where light struck it. The
rest of the bitumen could be dissolved
away, leaving a permanent image.
• Niépce and his partner Louis Daguerre
improved on Niépce’s camera greatly
in 1836, inventing the daguerrotype.
The daguerrotype image was truly
permanent—daguerrotype images
made in the 1830s are still viewable
today. With the development of the
daguerrotype, modern photography
had begun.
Other Applications of Lenses
• Movie projectors in their current form
were first developed in the 1890s. The
first commercially successful projector
was produced by Thomas Edison
in 1896. Film movie projectors for
commercial movies are gradually being
replaced by digital film projectors that
make use of DVDs or hard drives rather
than film.
• The magnifying glass was described
in Book of Optics by Ibn al-Haytham
in the year 1021. The device is simple,
yet powerful. The first observations of
bacteria and blood cells were made
by Antonie van Leeuwenhoek with
simple microscopes, another name for
magnifying glasses.
• The compound microscope, which uses
multiple lenses, was invented before
the simple microscope. Several designs
were produced from about 1600 to
1655.
• The compound telescope was invented
in the early 1600’s by Hans Lippershey,
a Dutch eyeglass maker and was used
by Galileo for observation and discovery
of the features of the surface of Jupiter
and Jupiter’s moons.
TEACHING NOTES
Engage
• Engage students by asking them to name all of the devices they can think of
that use some kind of photographic or optical image. Devices may include
film cameras, digital cameras, microscopes, telescopes, magnifying lenses,
eyeglasses, video cameras, and so on. Point out that all optical devices use a
lens and the principles developed in this chapter to function. Tell students
that they will be learning how some of these devices work in this section.
Explore and Explain
• Refer students to Figure 1 on page 567 of the Student Book and discuss how
the camera works. Because cameras are common and most students will have
one in some form (or have access to one), an understanding of how a camera
works will be more practical to students than some of the other devices
explained in this section.
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•
•
•
•
•
•
•
•
Ask, •Where is the object typically located, relative to F´ and 2F´? (beyond 2F´)
Now have students go to Figure 3 in Section 13.3. If the object is beyond 2F´,
where will the image appear? (between F and 2F) Where does the image appear
on the camera? (between F and 2F) How can the camera user get the image to
focus exactly on the film? (move the lens)
Still referring to Figure 1, ask, Why won’t you need to focus the camera if the
object is placed exactly at 2F´? (The image will appear exactly at 2F.) What will
happen to the image if the object is between 2F´ and F´? (The camera will not be
able to focus because the image will be beyond 2F.)
Distribute •BLM 13.5-1 Try This: Creating a Pinhole Camera. This BLM will
guide students through the process of creating a pinhole camera and using it
to take photographs.
Go over the other optical devices discussed in the section, spending extra time
on the lens arrangement and how the device functions, with a particular focus
on how it produces the image that humans want it to produce. Help students
compare each device to others and draw parallels or differences among them.
Explain that a movie projector does the opposite of a camera in that it
produces a large, inverted, real image from a small object. Because the
projector produces an inverted image, the film has to be run through
the projector upside down. An overhead projector functions in the same way
as a movie projector.
Explain that a magnifying glass is a simple converging lens. The human brain
extends the diverging rays backward to produce an enlarged virtual image.
Because a magnifying glass is small and can be made of light plastic, it would
be helpful to pass one or more of these around to students. Even though they
are probably familiar with a magnifying glass, it would likely be helpful to use
one now, having learned how it works.
Point out that Ibn al-Haytham was not only the first person to describe
the magnifying glass, as stated in the Did You Know? margin feature on
page 568 of the Student Book, he was also the first to describe a camera—
the simple pinhole camera called a camera obscura described in the Science
Background section.
Use a discussion with students to explain how the compound microscope is
able to create a magnified virtual image. Go over the process using a diagram
of Figure 6 (page 569 of the Student Book) on the board. Begin by drawing
just the object, objective lens, and real image. Ask, Why is the real image
slightly larger than the object? (The object is between F´ and 2F´.)
Next, add the eyepiece lens and observer to the drawing. Ask, What serves as
the “object” for the eyepiece lens? (the real image from the objective lens)
Why is the image now virtual and larger than the “object?” (The “object” is
closer than F´.) How is the compound microscope able to create such a magnified
image? (It enlarges the image twice—first creating a real image inside of the
microscope. Then a second magnification occurs in the eyepiece working like
a magnifying glass.)
Point out the similarities between the compound microscope and refracting
telescope. Both devices do similar things: they create a real image, then use
that real image as an object for a second eyepiece lens.
Extend and Assess
• Review each of the devices discussed in this section: the camera, the movie
projector, the magnifying glass, the compound microscope, and the refracting
telescope. Ask students to explain how each of the devices works. Encourage
them to state as many characteristics or features of each device as possible.
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Writing Tip
Writing a Critical Analysis
Encourage students to
present both sides of an
issue or the pros and cons
of any position when they
are writing. Point out that
being critical requires
examining all aspects of
the topic of their writing.
Unit Task Bookmark
The illustrations in this
section can be useful
to students as they
complete their optical
devices. By using these
diagrams in conjunction
with technical drawings
of primitive telescopes or
microscopes, they should
be able to understand the
principles at work.
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You may wish to do this as a small group activity by assigning each group one
of the devices. Each group should explain to the class how the device works.
• As an STSE extension, have students research the objective lenses used in
a telescope and the challenges involved in producing them. For example,
explain that such a lens could be a little more than a metre in diameter yet
be at the limits of its size due to sagging under the forces of gravity. Have
students research how it is possible that a disc of hard glass that has to be
quite thick could sag at all, much less enough to affect the performance of a
telescope. Have students prepare a brief report of their findings in a format of
their choice.
• Have students complete the Check Your Learning questions on page 570 of
the Student Book.
CHECK
YOUR LEARNING
Suggested Answers
1. Focusing moves the lens closer to or farther from the camera’s sensor to make the lens-to-sensor distance equal to
the image distance.
2. The first photographs were taken on glass plates coated with light-sensitive chemicals. Flexible rolls of film were
used next, followed in recent times by cameras equipped with digital sensors.
3. (a) A movie projector casts enlarged images on a screen, and if the film is beyond 2F´, the image will not be
enlarged.
(b) The film must be located between 2F´ and F´ to produce an enlarged image on a screen.
4. The film is oriented upside down in the projector.
5. Only in this location can the lens produce diverging rays that the observer’s brain can trace back to an enlarged
virtual image.
6. In each instrument, a real image is formed, but it lies inside the instrument’s body or tube.
7.
similarities
differences
use two converging lenses
refracting telescope is used for distant objects;
microscope is used for very close objects
objective lens makes a real image and eyepiece lens
makes a virtual image
refracting telescope is used to view very large objects;
microscope is used to view very small objects
observer sees an enlarged, virtual image
real image in a refracting telescope is smaller than life,
real image in a microscope is larger than life
8. (a) A refracting telescope produces an inverted image that makes the view seem upside down and thus confusing.
(b) In a terrestrial telescope, a third converging lens is added that corrects the view to appear right side up.
DIFFERENTIATED INSTRUCTION
• All students, particularly visual/spatial learners, should benefit from drawing
the diagrams in this section in their notebooks. Encourage students to
include labels and notes on their diagrams. Make sure that all diagrams are
related back to the basic optical relationships shown in Figure 3 and Figure 5
of Section 13.3. For example, ask, Why does the magnifying glass show an
enlarged, upright, virtual image? Students should recognize that the image
in the magnifying glass is virtual, upright, and larger than the object itself
because the object is located between the lens and F´.
• Repeat the process above for other devices in the section: camera, movie
projector, compound microscope, and refracting telescope.
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• Verbal/linguistic learners can explain the mechanism of each device in the
section by referring to Table 1 in Section 13.3. For example, ask, Why does
the movie projector show an enlarged, inverted, real image? Students should
recognize that the image in the projector is real, inverted compared to the
original, and larger than the object itself because the object is located between
the 2F´ and F´.
ENGLISH LANGUAGE LEARNERS
• Beginning with the word eyepiece, focus on compound words. Point out
first that eyepiece consists of two words put together: eye 1 piece. Give other
examples from the section and elsewhere: upgrade, shortcoming, eyeglasses,
weekend, baseball, sunlight, sandpaper, footprint, newspaper, fingernail. Have
students break down each compound word, define its components, and
define the word itself. Tell students to record the words in their notebooks.
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Computer Studies
Connection
Explain to students that
the detachable lenses that
are used on professional
cameras are actually a
combination of several
lenses and that these
lenses are designed
using computers.
Encourage students to
research the skills and
training necessary to
design camera lenses,
considering both the
computer knowledge and
the knowledge of optics.
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