19.3 Optical Instruments This telescope, located on the summit of Hawaii’s dormant Mauna Kea volcano, is one of the largest telescopes in the United States

19.3 Optical Instruments

This telescope, located on the summit of Hawaii’s dormant Mauna Kea volcano, is one of the largest telescopes in the United States.


Telescopes, microscopes, and cameras are all examples of optical instruments that enhance your ability to see.

These optical instruments all use lenses or mirrors, or a combination of the two, to reflect and refract light.


What are the two main types of telescopes?

Telescopes

There are two main types of telescopes, reflecting telescopes and refracting telescopes.


A telescope is an instrument that uses lenses or mirrors to collect and focus light from distant objects.

Telescopes


Reflecting Telescopes

The reflecting telescope uses mirrors and convex lenses to collect and focus light.

• Light strikes a large concave mirror and is brought to a focus.

• This focused light is reflected in a mirror and forms a real image.

• A convex lens magnifies the image.

Telescopes


Refracting Telescopes

The refracting telescope uses convex lenses to collect and focus light.

• Light from a distant object enters the telescope through a convex lens called the objective lens.

• The convex lens forms a real image inside the telescope.

• A convex lens magnifies this real image.

Telescopes


A. The reflecting telescope uses a large concave mirror to focus the incoming light rays.

Telescopes


B. The refracting telescope uses a series of lenses to focus light from distant objects.

Telescopes


How does a camera form an image on film?

A camera is an optical instrument that records an image of an object.

Cameras

Light rays enter a camera through an opening, are focused by the opening or lens, and form an image that is recorded on film or by a sensor.


Pinhole Camera

A simple pinhole camera can consist of a cardboard box with a small hole in one side.

• Light rays from the top and bottom of an object pass through the pinhole and cross paths.

• The rays form an upside-down, real image on the back wall of the box.

Cameras


Modern Film Camera

In a modern film camera, the lens elements focus the incoming light rays, which pass through the diaphragm that controls the amount of light.

• The lens must move toward or away from the film to focus an object.

• The shutter opens and the focused rays strike the film.

Cameras


The focused light reacts with a light-sensitive chemical coating on the film that records the real image. The image is upside down and smaller than the object.

Cameras


In a single lens reflex (SLR) camera, the mirror reflects the image through the viewfinder. When the shutter release button is pushed, the mirror flips up. The focused light rays pass through the lens system to the film.

Cameras

Film

Shutter

Shutter release button

ViewfinderPrism

MirrorLens elements

Diaphragm

Incoming light


What type of lenses does a compound microscope use to form an image?

Microscopes

The compound microscope uses two convex lenses to magnify small objects.


A microscope is an optical instrument that uses lenses to provide enlarged images of very small, near objects. A compound microscope has two convex lenses.

• Light rays from below pass up through the object and then pass through a convex lens called the objective.

• The lens produces an enlarged, upside-down, real image.

• The eyepiece enlarges the image.

Microscopes


This compound microscope uses a mirror to reflect light up and into the microscope.

Microscopes

Mirror

Slide with specimen

Objective lens

Eyepiece lens


Assessment Questions

1. A refracting telescope collects and focuses light from distant stars with a a. convex lens.

b. concave lens.

c. convex mirror.

d. concave mirror.



1. A refracting telescope collects and focuses light from distant stars with a a. convex lens.

b. concave lens.

c. convex mirror.

d. concave mirror.

ANS: A



2. How is a camera brought into focus? a. The type of film or sensor is matched to the amount of

light.b. Lenses are moved closer to or farther from the film or

sensor.c. Lenses are moved closer to or farther from other

lenses.d. The mirror changes the length of the light path in the

camera.



2. How is a camera brought into focus? a. The type of film or sensor is matched to the amount of

light.b. Lenses are moved closer to or farther from the film or

sensor.c. Lenses are moved closer to or farther from other

lenses.d. The mirror changes the length of the light path in the

camera.

ANS: B

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19.3 Optical Instruments This telescope, located on the summit of Hawaii’s dormant Mauna Kea volcano, is one of the largest telescopes in the United States