A periscope is a device that lets you see over or around an obstacle, where you don’t have a direct line-of-sight view. Submarines use periscopes for scanning the air and water surface above them. Periscopes also offer views over walls and around corners. Periscopes are useful, fun, and a great way of learning about light and optics. Here is a simple project for making a periscope. The basic project is perfect for grade school students, while using improved materials and optics challenges more experienced explorers.
How a Periscope Works
The simplest periscope consists of a tube with mirrors at either end that are set parallel to each other and at a 45° angle. Alternatively, prisms in the place of mirrors also work. More advanced instruments use a series of prisms and lenses.
If the mirrors are not exactly parallel or at a 45° angle, the periscope still works, but this reduces its field of view. The basic principle is that light strikes the surface of the mirror or prism. According to the law of reflection, light bounces off perpendicular or at a 90° angle. This directs it to the second mirror or prism, where the same process occurs.
There are many ways of making a periscope. Choose materials according to availability and age-appropriateness. For example, a simple cardboard periscope using hand mirrors only requires scissors. A sturdy periscope using PVC tubes and cut mirrors requires a saw and may introduce sharp glass edges.
- Long tube
- 2 Mirrors
Good options for the tube include a paper towel or wrapping paper roll or a long box. Good mirror choices include basic hand mirrors. If these are unavailable, sheets of aluminum foil or Mylar are also reflective, although their image won’t be as clear. Make sure the mirror is a bit wider than the tube. Stick the mirror to the tube using tape, glue, putty, or adhesive stickers. There are a few ways of measuring the 45° angle. You can print a protractor (best) or just eyeballing it using a rubber band (good). Remember, 45° is half of a right angle.
How to Make a Periscope
- Measure the 45° angles or else place rubber bands at both ends of the tube and slide them so they appear parallel to each other. Either mark the angle with a pen or pencil or else leave the rubber bands in place.
- Cut both ends of the tube. The slanted ends are where the mirrors sit. But, before you secure the mirrors, you need openings on either end of the tube for viewing. These openings go down from the pointed sides of the tube. Go ahead and cut them.
- Place the mirrors and tape or glue them in place. Look through the openings and adjust their size and shape as needed.
That’s it! It’s simple. Here’s a video showing exactly what you do:
More Advanced Options
A paper and foil or mirror periscope works great, but it’s not particularly sturdy or weatherproof. Make a better instrument using a PVC pipe and two elbow joints. Attach the mirrors inside the elbow joints and fit the joints onto the tube. The PVC design also offers the advantage of letting you swivel the periscope view. If you use two PVC tubes, where one slides into the other, you also get a periscope that you can raise or lower.
- Lekner, John (1987). Theory of Reflection of Electromagnetic and Particle Waves. Springer. ISBN 9789024734184.
- Walker, Bruce H. (2000). Optical Design for Visual Systems. SPIE Press. ISBN 978-0-8194-3886-7.