Light & Optics

Shoebox Camera Obscura

Turn a shoebox into a working camera with one pinhole and no lens, then find out why a smaller hole gives you a sharper picture and a dimmer one.

Medium · 1 hour

Introduction

Before there were lenses, before there was film, there was a dark room with a small hole in one wall. The picture that lands on the opposite wall is upside down, in full color, and completely real.

A shoebox is a dark room. You need one hole, one piece of tracing paper, and about an hour.

The Why

Light travels in straight lines. A single point on a bright tree outside is throwing rays in every direction, but only the ones aimed at your tiny hole get through, and those carry straight on to land on one spot inside the box. Rays from the top of the tree end up at the bottom of your picture and rays from the bottom end up at the top, which is why the image arrives upside down. This is also what the back of your eye receives, and your brain quietly flips it for you.

Step-by-Step Instructions

1
Cut a square hole about 3 cm across in the middle of one end of the box, and a larger viewing window in the opposite end.
2
Tape tracing paper tightly across the viewing window. This is your screen, and it has to be flat rather than baggy.
3
Paint or line the inside of the box black. Every bit of stray light bouncing around in there washes out the picture.
4
Tape a square of foil over the 3 cm hole, then push a pin straight through the center of the foil to make one clean pinhole. Do not wiggle it.
5
Seal every seam and corner with black tape, then take the box to a bright window or outside on a sunny day.
6
Put the cloth over your head and over the viewing end, and look at the tracing paper while the pinhole faces something bright. Give your eyes a full minute to adjust before you decide it is not working.
7
Make a second foil square with a noticeably bigger hole and a third with a smaller one. Swap them in turn and write down what happens to sharpness and to brightness each time.

Pinhole Comparison

One row per hole. Score sharpness and brightness from 1 to 5, always on the same view through the same window.

Hole	Roughly how wide	Sharpness 1-5	Brightness 1-5	What you could make out
Row 1, Hole	Row 1, Roughly how wide	Row 1, Sharpness 1-5	Row 1, Brightness 1-5	Row 1, What you could make out
Row 2, Hole	Row 2, Roughly how wide	Row 2, Sharpness 1-5	Row 2, Brightness 1-5	Row 2, What you could make out
Row 3, Hole	Row 3, Roughly how wide	Row 3, Sharpness 1-5	Row 3, Brightness 1-5	Row 3, What you could make out
Row 4, Hole	Row 4, Roughly how wide	Row 4, Sharpness 1-5	Row 4, Brightness 1-5	Row 4, What you could make out
Row 5, Hole	Row 5, Roughly how wide	Row 5, Sharpness 1-5	Row 5, Brightness 1-5	Row 5, What you could make out

Keep the subject and the light the same for every row. If the sun goes behind a cloud between two rows, the brightness column stops meaning anything.

Materials List

A shoebox with a lid, or any box you can seal light-tight
Aluminum foil
Tracing paper, baking parchment, or thin white paper
A pin or a needle
Black tape, and black paint or black paper for the inside
Scissors and a ruler
A dark cloth or towel to put over your head

Safety First!

Never point the box at the sun and never look toward the sun through it, not even on tracing paper. Get adult help with the scissors and with cutting the box. If you spray paint the inside, do that outdoors with an adult.

Challenge Mode

Find the best hole. Going smaller makes the picture sharper, but only up to a point: below about half a millimeter it starts to blur again, because light passing through a very small opening spreads out instead of continuing straight. That spreading is called diffraction, and it is the same effect that puts stripes on the wall in the double slit project. Find the hole size where your box is sharpest, and record what happens on either side of it.