DIY Periscope from Cardboard and Mirrors

A periscope uses two mirrors angled at 45° to redirect your line of sight around corners or over obstacles. Submarines use the same principle. This cardboard version costs almost nothing to build and clearly demonstrates the law of reflection.

What You’ll Need

• Long cardboard tube or rectangular cardboard box (at least 30 cm tall)
• 2 small flat mirrors (approx. 5 × 5 cm) — available from craft stores
• Ruler, pencil, and craft knife or scissors
• Strong adhesive tape or hot glue gun
• Black paint (optional, reduces internal reflections)

Step-by-Step Instructions

1. Cut the tube: If using a flat cardboard sheet, roll it into a rectangular tube about 5 × 5 cm in cross-section and tape the seam. Cut the tube to your desired length (30–50 cm works well).
2. Mark mirror slots: At the bottom of the tube, mark a slot at 45° angle to the tube’s axis. Repeat at the top, rotated 90° around the tube so the two mirrors face opposite directions.
3. Cut viewing holes: At the bottom, cut a rectangular hole on the front face so you can look in. At the top, cut a corresponding hole on the opposite face so light can enter.
4. Install mirrors: Slide each mirror into its 45° slot, reflective face pointing toward the opposite hole. Secure with hot glue or tape on the edges.
5. Test and adjust: Look through the bottom hole — you should see what is directly above the top hole. Adjust mirror angles slightly if the image is off-centre.

Safety Notes

• Use care when cutting with a craft knife — always cut away from your body and use a cutting mat.
• Broken mirror edges are sharp; handle with care and dispose of broken pieces safely.

Tips & Troubleshooting

• Paint the inside of the tube black to reduce stray light and improve image clarity.
• For a longer periscope, join two tubes together and ensure the mirrors are aligned before gluing.
• Acrylic mirrors (available cheaply online) are safer than glass mirrors for kids’ projects.