To make a camera obscura, blacken the inside of a deep box, prick a hole with a needle in a square of aluminium stuck over one end, stretch a sheet of tracing paper across the opposite end, then point the hole at a bright scene to see the image appear on the tracing paper.
Watching the outside world draw itself upside down on a sheet of tracing paper, moving and in colour, from a simple box with a hole in it: that is what a camera obscura lets you do, and making one takes less equipment than you might think. The aim here is to observe the image as it forms, directly with your own eyes.
In short, in 6 steps:
- Gather a deep box, a sheet of tracing paper, a square of thin aluminium, a needle, matt black paint and black tape
- Blacken the inside of the box with matt black paint or black card
- Cut a window of one to two centimetres in one end and stick the aluminium square over it
- Prick the hole with the needle, about one millimetre across
- Stretch the tracing paper perfectly flat across the opposite end
- Point the hole at a very bright scene and look at the tracing paper, blocking out the ambient light with your hands
You are not trying to record the image on sensitive paper, you are trying to look at it. If the mechanics of the camera obscura principle interest you before you start making things, remember that it comes down to a single idea: light travels in straight lines. This principle is also the starting point for all pinhole photography.
What sets the camera obscura apart from the camera
An observation camera obscura and a pinhole camera share exactly the same core, a black enclosure with a single hole. What separates them is what you place at the back, where the image forms.
In the camera obscura we are going to build, the back is a translucent screen, a sheet of tracing paper or baking paper, on which the image appears and is viewed live. Nothing is fixed: the image lives for as long as you watch it, then disappears as soon as you put the box away.
The moment you want to keep this image, you have to replace the tracing-paper screen with a photosensitive surface and move on to chemistry: you are then making a pinhole camera. Here, you observe; you record nothing.
The Sténoflex kit provides this ready-made dark chamber with its paper and chemicals, for anyone who wants to take that step after observing the projected image.
Materials for a box camera obscura
Everything comes from ordinary objects, and most of the care goes into the blackness and the hole.
- A fairly deep cardboard box, such as a shoebox, or a long packing box.
- A sheet of tracing paper or baking paper for the screen.
- A small square of thin aluminium, cut from a drinks can, to make a clean hole.
- A fine needle and matt black paint or black card for the inside.
- Opaque black tape to seal light leaks.
It is the same requirement as for any pinhole camera, with one nuance: for observing, the box does not have to be completely light-tight, since there is no paper to fog.
Making the hole and fitting the screen
The hole is made in the aluminium, never in the thick cardboard, which would give a rough edge and a muddled image. Cut a window of one to two centimetres in one end of the box, stick the aluminium square over it with black tape, then prick the hole with the needle, turning it gently.
At the opposite end, stretch the tracing paper perfectly flat: this is what receives the image. The longer the box, the larger but dimmer the projected image, whereas a short box makes it smaller and brighter.
What hole size to see the image clearly
For simple observation, a hole of about one millimetre offers a good compromise between sharpness and brightness. Too small, and the image becomes dark and hard to make out with the eye, whereas a photographic pinhole aims instead for fineness at the expense of brightness.
For a sharper image, make the hole in the aluminium rather than in thick cardboard, which would give a rough edge and a muddled image, and keep it perfectly round, with no burr.
Watching the image projected upside down
Place the box facing a very bright scene, a sunny window or a landscape in broad daylight, with the hole pointing towards the light. Bring your eye close to the tracing-paper screen, cupping your hands around it to block out the ambient light, and give your eyes a few seconds to adjust.
The image then appears, soft, in colour and reversed top to bottom and left to right, because light rays travel in straight lines and cross as they pass through the hole; it is by making the box that you truly grasp why the image ends up upside down. This is precisely the phenomenon that the camera obscura shows better than any diagram.
Turning a room into a camera obscura
The principle works perfectly well without a box, and all you need to experience it on a large scale is a room that can be plunged into darkness. It was in this form, as a room that people entered to see the outside world projected onto the wall, that the camera obscura was first observed, long before photography, by the long line of observers who described this phenomenon from Antiquity to Ibn al-Haytham.
Choose a room with a single window looking onto a sunny scene. Black it out with cardboard or an opaque tarpaulin until it is as dark as you can make it, then make a hole of one to two centimetres in this screen and let your eyes adjust for a good minute.
On the opposite wall, the landscape outside then appears in full, inverted, in a muted light. The image is faint and calls for patience, but the effect is striking and brings to life a phenomenon that is several centuries old.
If you are running the activity with children, have them observe this image before moving on to taking pictures.
From the observed image to the recorded image
Making a camera obscura is a very direct way to understand, with your own eyes, what happens in every pinhole camera: a hole, darkness, a reversed image at the back. As long as you stick with the tracing-paper screen or the wall, you observe without keeping anything.
To record this image instead of watching it disappear, you have to replace the tracing-paper screen with a sensitive surface and move on to chemistry, which marks the boundary between observation and photography.
Éric Marais — Photographer, author of two books on pinhole photography (published by Pearson) and creator of the Sténoflex. He has run introductory workshops in pinhole photography and analogue developing from the very beginning.