Building a Periscope

All you need to make a periscope is two mirrors and something on which to mount them. Then you can see around and over barriers, spy above walls, and study animals without disturbing them. Periscopes are used in submarines to see above the water; but with special materials and some effort you can build a periscope to see down into the water. Adding lenses to your periscope in the right combination can improve the viewing experience.

Be sure to read this activity in its entirety before you begin (as you should with all activities). There are several variations on design, and the one you choose will determine your approach and materials.

Materials

For mirrors, you can use dental mirrors. Have an adult use a jeweler's saw to saw off each handle near the mirror, leaving the mirror in the plastic mount.

For Plexiglas Periscope

For Plywood Periscope

• 60-by-90-by-O.3-cm sheet of Plexiglas or plywood (available at hardware stores)
• meterstick
• black spray paint
• silicone aquarium or bathroom sealant (optional)
• 2 small mirrors
• 2 weak convex lenses (from an old pair of eyeglasses or available from science suppliers, such as Edmund Scientific—optional)
• epoxy (if using lenses)
• Plexiglas cutter (a scorer that cuts a small groove to enable you to break the Plexiglas cleanly—requires adult help)
• plastic glue
• duct tape and scissors
• table saw (requires adult help)
• waterproof paint (optional)
• finishing nails and hammer
• Plexiglas to cover openings (optional)

Procedure

You can widen the field of view in your periscope by adding a weak convex lens next to each mirror, positioned parallel to each other and to the ends of the periscope. Use epoxy to affix the lenses. Things will look smaller than they do in real life. but you will be able to see more.

1. Build the body of your periscope from Plexiglas or plywood.

   

   1. Design and build a long four-sided chamber with openings at opposite sides of each end, as shown. The dimensions of the side walls are up to you—a good size to start with is 70 by 4 cm. Your device will operate best if you paint the inside walls black before assembling.
   2. If using Plexiglas, have an adult cut the walls of the periscope and join them with plastic glue. Allow the glue to dry.
   3. If using plywood, have an adult use a table saw to cut out the walls.
   4. If you intend to use your periscope in the water, join all edges with aquarium sealant. You will want to treat the plywood with an undercoat of a couple coats of waterproof paint after applying the sealant.
   5. In some cases, it may be useful to reinforce your periscope with thin strips of duct tape (for Plexiglas) or small finishing nails (for plywood).
2. Lay your periscope flat on a table and position the mirrors parallel to each other, at each opening, with the reflective surfaces facing each other. Adjust them so that when you look in one opening (the eyehole), you can see distant objects through the other opening (the viewer). When the mirrors are lined up properly (calibrated), glue them to the sides with aquarium sealant.
3. When your periscope is dry, practice viewing through it. Look over a wall, under a table, around a corner, and down a hole.

To Make an Underwater Periscope

If you have made your periscope with waterproof walls, you may want to take the mirror near the eyehole out so you can look straight down into the periscope. This will be more comfortable when you are leaning over a dock. The only remaining openings should be at the eyehole and the viewer, where the light travels in and out. Cover the openings with slightly larger pieces of Plexiglas, and glue them in place with sealant. Allow the pieces to dry overnight, and inspect carefully for leaks. If you have a good seal, you can dip the lower end into a pond and start using your viewing instrument to study underwater ecology.

References

Experiments with Light and Mirrors (Getting Started in Science series) by Robert Gardner (Berkeley Heights. N.J.: Enslow. 1995).

Making Light Work: The Science of Optics (Xperiment! series) by David Darling (parsippany. N.J.: Silver Burdette. 1991).

The Optics Book: Fun Experiments with Light. Vision and Color by Sharon Levine and Leslie Johnstone (New York: Sterling. 1998).

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