You’re stuck in the back of a crowd. Maybe you’re trying to see over a fence or you're just playing a high-stakes game of hide-and-seek with the kids. Your first instinct is to grab your phone and hold it up high, right? But there is something visceral and tactile about using mirrors to bend light. It’s physics in your hands. Honestly, learning how to make a periscope is one of those "aha!" moments where science stops being a textbook chapter and starts being a superpower.
It’s about line of sight. Basically, a periscope is just a tube with mirrors at both ends, set at specific angles so you can see things that are otherwise out of view. It’s the same tech—though way more primitive—that submariners used for decades before high-tech photonics masts took over.
The Weird History of Seeing Around Corners
We usually think of submarines when we talk about periscopes. However, the history goes way back. Johannes Gutenberg—yeah, the printing press guy—actually sold periscopes in the 1430s. He marketed them to pilgrims so they could see over the heads of crowds at religious festivals. He called them Spiegel (mirrors).
Fast forward to the trenches of World War I. Soldiers couldn't poke their heads up without getting shot, so they used "trench periscopes." These weren't fancy. Often, they were just two mirrors strapped to a stick. It was life or death DIY. When you’re making one today, you’re basically tapping into 600 years of "I need to see what's over there without being seen."
Gathering Your Supplies
Don’t overthink this. You don't need a lab. You need trash, mostly.
- A long box: A milk carton (quart or half-gallon) is the classic choice because it’s sturdy and waterproof. Two cereal boxes taped together work if you want more height. A PVC pipe is the "pro" version, but it's harder to cut.
- Two small mirrors: These need to be flat (plane mirrors). Don’t use curved ones unless you want a funhouse effect. You can find these at craft stores or even pry them out of old makeup compacts.
- Tape or Glue: Duct tape is ugly but reliable. A hot glue gun is better for positioning.
- A craft knife: To cut the box. Be careful. Seriously.
- A protractor: If you want to be precise. If not, you can eyeball it, but your "image" might be a bit wonky.
How to Make a Periscope That Actually Works
First, if you're using a milk carton, wash it. Nobody wants a periscope that smells like spoiled dairy. Cut off the peaked top so you have a flat-ended rectangular prism.
Setting the Angles
This is where people mess up. The mirrors must be at a 45-degree angle. If they aren't, you'll end up looking at the inside wall of your box instead of the horizon.
Place your first mirror near the top of the box. You’ll need to cut a hole (a window) on one side of the box that is slightly smaller than your mirror. Face the mirror toward that hole, tilted down at 45 degrees.
Now, go to the bottom. Cut another window, but on the opposite side of the box. This is crucial. If the windows are on the same side, you’ll just be looking at the back of your own head. Place the second mirror at the bottom window, tilted up at 45 degrees.
The Law of Reflection
Why 45 degrees? It’s the law of reflection. In physics, the angle of incidence equals the angle of reflection ($\theta_i = \theta_r$). When light hits the top mirror at 45 degrees, it reflects down at 45 degrees, traveling straight down the tube. It hits the bottom mirror and does the same thing, bouncing straight out into your eye.
Common Mistakes People Make
Most DIY guides make this sound foolproof. It isn't.
The Double-Image Ghost: If you use mirrors that are too thick, or if they are "second-surface" mirrors (where the silvering is behind a thick layer of glass), you might see a faint ghost image. This happens because light reflects off both the glass surface and the silvering. For a toy, it doesn’t matter. For a "spy" tool, it’s annoying.
The Wobbly Mirror: If your mirror shifts even half a degree, your view will be crooked. Use a lot of tape. Or better yet, build a little cardboard "shelf" inside the box at a 45-degree angle to rest the mirror on.
Tunnel Vision: If your tube is too long and your mirrors are too small, you'll feel like you're looking through a straw. Keep the tube wide or the mirrors large to maximize your field of view.
Why This Matters in 2026
We live in a world of 4K cameras and drones. Why bother with cardboard and glass?
Because it’s analog. It doesn't need a battery. It doesn't have a lag. It doesn't get hacked. Understanding how to make a periscope teaches you about the behavior of light in a way a YouTube video never can. You're manipulating photons.
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Plus, there’s the "Stealth" factor. If you’re a bird watcher, a periscope lets you look over a bush without scaring away a nesting warbler. If you're a parent, it's the cheapest way to keep a kid occupied for three hours. They’ll start investigating the "hidden worlds" under the sofa or over the kitchen counter.
Advanced Modifications
Once you've mastered the basic box, try these:
- The Rotating Head: Instead of one long box, use two tubes—one slightly smaller than the other. Slide the smaller one into the larger one. Now you can rotate the top mirror 360 degrees while the bottom mirror stays fixed at your eye.
- Magnification: If you're feeling brave, try taping a magnifying glass over the "objective" (top) window. It gets tricky because you have to manage focal lengths, but it's possible.
- The PVC "Peripro": Use 2-inch PVC pipe and two 90-degree elbow joints. You can pop the mirrors into the elbows. It’s indestructible and looks way cooler than a Cheerios box.
Actionable Steps to Build Yours Today
Don't just read about it. Go to the kitchen.
- Find a box. Any box.
- Measure the width of your mirrors before you cut your windows.
- Use a protractor to mark that 45-degree line on the side of the box. Precision here pays off in image clarity later.
- Secure the mirrors with more adhesive than you think you need. Vibrations or accidental drops will knock them out of alignment.
- Test it out. Go to a door, stay behind it, and use the periscope to see who is in the hallway.
The beauty of this project is its simplicity. It's a bridge between the physical world and our perception of it. You're literally bending the path of light to suit your needs. That's not just a craft project; it's basic engineering that has remained unchanged for centuries because, frankly, you can't improve on the laws of physics.