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Optics: An Educator’s Guide With Activities in Science and Mathematics EG-2000-10-64-MSFC 53
Level: Grades (9–12)
Activity: 15
Building a Telescope
Theory
A
B
Objective
Science and Mathematics Standards
Materials
In a telescope, the lens held next to your eye is called the eyepiece and is usually a short focal length lens or a combination of lenses. The lens at the other end of the telescope is called the objective lens. Light from a distant object is focused by the objective lens to form an image in front of the eyepiece. The eyepiece acts as a magnifier and enlarges that image. The magnification of the telescope can be found by dividing the focal length of the objective by the focal length of the eyepiece.
- 2 converging lenses (convex lenses)
- telescoping tubes (mailing tubes)
- manila file folder
- scissors
- knife or saw
- glue
- 1 white poster board
- red and black tape
The student will construct a simple refracting telescope and calculate the magnification.
Science Standards Science as Inquiry Physical Science
Mathematics Standards Problem Solving Communication Connection Computation/Estimation Measurement
Lenses, Refraction
Light, Color, and Their Uses
Optics: An Educator’s Guide With Activities in Science and Mathematics EG-2000-10-64-MSFC
A B C D
Procedures
This telescope will be constructed using the same lenses that were used in the experiment named, “Focusing Light With a Lens,” page 49.
- The mailing tubes will be the body of the telescope with the smaller one sliding inside the larger one. The length of the assembled telescope will be a little longer than the sum of the focal lengths of the two lenses. Add the value of the focal lengths of the short and long lens together. Divide that length by two and then add another inch. Cut both of the tubes to that length with a knife or saw.
- Use the scissors to cut out two circles from the manila paper that are the same size as the diameter of the mailing tube. These circle frames will mount and center the lenses on the tube. With a knife, cut out circles that are slightly smaller than the
diameter of the lenses in the center of the paper frame circle. Glue the lenses to the center of the frame. The shorter focal length lens will be the eyepiece. Glue that framed lens to the end of the smaller tube. Glue the other framed lens to the end of the larger tube.
- Slide the two cardboard tubes together. You have now assembled a simple refracting telescope. Look through the eyepiece of your telescope and focus it on a distant object. Slide the two cardboard tubes in and out until you have a clear image. What do you observe?
- Use the red and black tape to make stripes on the white posterboard (see illustration on page 55) to use as a chart.
Larger mailing tube
Lens with shortest focal length (eyepiece)
Manila frame
Lens with longest focal length (objective lens)
Manila frame
Light, Color, and Their Uses
Optics: An Educator’s Guide With Activities in Science and Mathematics EG-2000-10-64-MSFC
Converging lenses can be found in many of the everyday items we see in our homes. How many can you find? Here are a few examples: Paperweights, fish bowls with water in them, bottoms of soda bottles, etc.
Junior Home Scientist
Diagonal Mirror
Eyepiece
Parabolic Mirror
Newtonian Reflector Telescope
Lens
Lens
Eyepiece
Objective Lens
Refractor Telescope
Most astronomical telescopes are reflectors. Objective mirrors are easier to make than objective lenses. Large mirrors are structurally easier to design and less expensive to build than large lenses.
