Pinhole Camera Experiment: An Image Without a Lens

A hole can take a photograph. Not a metaphorical hole: an actual 0.6 mm pinprick in kitchen foil, which projects a complete, upside-down, full-colour image of your garden onto a piece of tracing paper. No glass, no lens, no focusing. The pinhole camera experiment is the cleanest demonstration in all of optics of what an image actually is, and the moment a child sees a recognisable upside-down version of the window appear on the paper, the abstract claim that light travels in straight lines becomes something they have witnessed. One rule governs everything below, and it is not negotiable: a pinhole camera is for projecting an image. You never point it at the sun and look through it.

Key Takeaways

• You make a small hole in foil at one end of a 20 cm tube and a translucent screen 5 cm from the other end, then look in from the open end with your head under a dark cloth.
• The image is upside down and left-right reversed, in full colour, and dim. The dimness is the main reason home attempts fail.
• Hole size matters and has an optimum: roughly 0.6 mm for a 20 cm tube. Too small is blurry from diffraction, too large is blurry from geometry.
• Never look through any pinhole device at the sun. To see the sun, you project its image onto a card and look at the card with your back to the sun.
• Best for ages 8 to 14, with an adult doing the cutting.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Rigid cardboard tube, 20–25 cm	1	A crisp tube with a metal base is ideal	Roll stiff black card into a tube and tape it; a long shoebox also works
Kitchen foil	A 10 cm square	n/a	Black card with a needle hole, though foil takes a cleaner hole
Tracing paper or greaseproof paper	A 10 cm square	Stationery or supermarket	Thin white paper, which is dimmer, or a frosted sandwich bag
Sewing needle, size 7 or 8	1	Sewing kit	A pin. Avoid a thick darning needle; the hole will be too big
Craft knife and cutting mat	1	n/a	Adult only. Scissors will do if your tube is card rather than metal-based
Black electrical or gaffer tape	1 roll	n/a	Any opaque tape. Light leaks ruin this experiment
Dark cloth, jacket or towel	1	n/a	Needed as a hood. Without it you will probably see nothing
Ruler	1	n/a	n/a

Time: prep 25 min, experiment 20 min, cleanup 5 min Cost: everything is probably in the house Mess level: low, though cutting the tube makes cardboard dust

Do the Experiment: The Pinhole Camera Experiment

Step 1 - Cut the tube and make the screen

An adult cuts cleanly around the tube 5 cm from the closed end, giving a short piece with the base and a long open piece. If the base is metal, tape over the cut rim immediately; cut tin is genuinely sharp. Tape tracing paper tightly across the open end of the short piece, flat and without wrinkles.

Step 2 - Make the hole the right size

Tape a square of foil over the closed base, or pierce the base directly if it is card. Rest the foil on a soft surface and push the needle through just until the tip emerges, then rotate it a quarter turn and withdraw. Hold it to a light: the hole should be a barely visible pinprick, about 0.5 to 0.7 mm. That is the optimum for a 20 cm tube, for reasons in the mechanism section.

Step 3 - Reassemble and seal every light leak

Slide the long tube over the short piece so the tracing-paper screen sits inside, about 20 cm from the hole. Tape the joint all the way round with opaque tape. Any stray light entering the tube between hole and screen will wash out the image, and this step is where careful work pays off.

Step 4 - Predict, then look

Before looking, ask: “Will the picture be the right way up, upside down, or mirrored? And will it be in colour?” Nearly everyone gets at least one of those wrong. Write the prediction down. Then point the hole at a bright window or a sunlit street, put the open end to your face, and drape the cloth over your head and the tube.

What you should see: Nothing, for about twenty seconds, while your eyes dark-adapt. Then a faint, soft, full-colour image on the paper, upside down and left-right reversed. Bright windows, car headlights and sunlit walls appear first; shadowed detail may never appear at all. Do not expect a phone-screen image. Expect a ghost.

Step 5 - Measure the magnification

Point it at something whose size you know, such as a doorway 3 m away, and estimate the image height on the screen with a ruler held against the paper.

What you should see: The image height divided by the object height should equal the screen distance divided by the object distance: 0.20 m ÷ 3 m, or about 1/15. A 2 m doorway should give a 13 cm image, which will not fit on the screen, so use the bottom half of the door and check that instead.

Step 6 - Change the hole and watch the trade-off

Make a second foil square with a deliberately large hole, about 3 mm, and swap it in.

What you should see: A much brighter image that is noticeably blurrier. Then try a third foil with a hole as small as you can make it, which gives a dimmer image that is also blurry, this time from diffraction. The middle size wins, which is the whole point of Step 2.

Step 7 - Scale it up to a whole room

Cover a window with cardboard and black plastic, leaving one hole about 3 mm across, in a room with a white wall 3 to 4 m away. Make the room as dark as you can and wait two or three minutes.

What you should see: The street outside, upside down, across the wall, in colour, with moving cars. This is a camera obscura and it is the single most memorable version of the experiment. It needs patience and genuinely good blackout.

What’s Actually Going On

Every point on an object scatters light in all directions. That is why you can see a chair from anywhere in the room. It is also why a bare screen held up in daylight shows no image: light from every point on the scene arrives at every point on the screen, and the result averages to a uniform grey.

A pinhole fixes that by discarding almost everything. From any given point on the object, only the narrow pencil of rays aimed at the hole gets through, and that pencil lands on one small patch of the screen. Points above the hole’s axis project below it, and points to the left project to the right, because the rays cross at the hole. So the image is inverted in both directions. The mapping is one-to-one, which is the definition of an image, and no lens is required to create it; a lens only gathers more light from each point and brings it back to a focus.

Magnification follows from similar triangles: image size divided by object size equals screen distance divided by object distance. One consequence is worth knowing before you point the thing at the sky. The sun and the moon both subtend about 0.5°, so a pinhole produces an image of either whose diameter is roughly the screen distance divided by 108. With a 20 cm tube, that is 1.8 mm, far too small to show anything. In a 4 m room it becomes 3.7 cm, which is why solar projection needs a long throw.

Sharpness is a fight between two effects. Geometric blur is set by the hole itself: a hole of diameter d smears each point into a patch roughly d across, so smaller is sharper. Diffraction works the other way: light passing through an aperture spreads by an angle of about 1.22λ/d, which at the screen gives a blur of roughly 2.44λf/d, so smaller is blurrier. Adding the two and minimising gives an optimum near d ≈ 1.9√(λf), the result usually attributed to Rayleigh. For green light at 550 nm and f = 200 mm, that is 0.63 mm. Matt Young’s 1971 treatment in Applied Optics and Ian Stephenson’s 2009 paper in The Imaging Science Journal both work through pinhole resolution and diffraction limiting in detail if you want the full derivation.

Two things people get wrong. The first is expecting a focused image: a pinhole camera has no focus at all, no distance at which it becomes sharp, which is also why it has effectively infinite depth of field. The second is thinking the hole must be round. It helps, but a ragged hole still forms an image, just with a larger blur patch.

How to Explain It to Your Kid

Ages 5–8: The hole only lets one straight line of light through from each place

Hold a torch and show them that light goes in straight lines by blocking it with your hand. Then say the hole is so small that from each spot on the tree outside, only one thin straight line of light can get in, so each spot lands in one place on the paper and the picture builds itself. Let them look as long as they want under the cloth, and let them find the upside-down bit on their own rather than telling them.

Ages 9–12: Similar triangles and a real measurement

Draw the two triangles: object to hole, hole to screen. Then do the magnification measurement in Step 5 and check the prediction against the ruler. The ratio of the sides is the whole story, and it is the same mathematics used in how a digital camera sensor turns light into pixels, minus the lens. Then let them calculate how big a 4 m room would make the moon look.

Ages 13+: Optimise the hole and justify it

Give them the two blur terms, d for geometry and 2.44λf/d for diffraction, and have them plot both against d on the same axes for f = 200 mm. The crossing point is the optimum, and deriving 0.6 mm themselves is far better than being told. Then extend: how would the optimum change for a 1 m tube, and what does that say about why large-format pinhole photographers use holes near a millimetre?

The question to ask: “If I made a second hole in the foil, 1 cm away from the first, what would appear on the screen? One picture, two pictures, or a blur? Decide before we do it.”

Why Teaching This Early Pays Off

Image formation is one of the genuinely hard ideas in school physics, and the difficulty is specific: students learn ray diagrams for lenses before they accept that an image is a point-to-point correspondence rather than a thing that travels. Galili and Hazan’s 2000 study in the International Journal of Science Education documented how often learners treat the image as an object that moves from the lens to the screen. A pinhole removes the lens entirely, which strips the concept back to the geometry and makes the correspondence visible.

It also pre-loads a surprising amount of later material. Depth of field, aperture and exposure in photography; the inverse-square dimming of a projected image; the resolution limit of a telescope; why your own pupil constricts in bright light at a cost in sharpness. All of these are the same two competing blur terms in different clothes.

One honest note on expectations. This is a patience experiment, not a spectacle. Roughly half of families who try it see nothing on the first attempt because the room was too bright or they did not wait for dark adaptation. If you treat the first failure as part of the procedure rather than a disappointment, you will probably get there on the second try, and the thing a child remembers is the image, not the wait.

Before You Start: What Parents Should Know

Best age	8 to 14. Younger children can look through one an adult has built
Supervision	Adult required for cutting, and adult present for any use outdoors
Real hazards	Solar viewing. Looking at the sun through any pinhole device can cause solar retinopathy, which may be permanent and is often painless as it happens. NASA states that the only safe direct view of the sun is through certified ISO 12312-2 eclipse glasses or a purpose-made solar filter. Sunglasses, several pairs stacked, exposed photographic film, smoked glass, a CD, a space blanket and welding glass below shade 12 are all unsafe. A cut metal tube rim is sharp; tape it. Craft knives are for adults
Don’t	Don’t use this as a “solar viewer” by looking through it. To see the sun or an eclipse, stand with your back to the sun, hold the pinhole card up and let the image fall on a second card held below it, then look at that card

When It Doesn’t Work

• You see nothing at all. Most common by far, and usually three things at once: the room is too bright, you have not waited 20 to 30 seconds for dark adaptation, and the cloth is not sealing out side light. Point at the brightest thing available, cover your head properly, and wait.
• A bright blur instead of an image. The hole is too big. Make a fresh foil square with a finer needle. If you can see the hole clearly without holding it to a light, it is too big.
• A dim blur instead of an image. The hole is too small, or torn and ragged. Diffraction dominates below about 0.3 mm on a 20 cm tube.
• Grey fog on the screen. Light is leaking into the tube between the hole and the screen. Tape every seam with opaque tape and check for pinpricks by looking into the open end in a dark room with the hole covered.

Take It Further

• Make it a camera that records. Replace the tracing-paper screen with a piece of photographic paper or a sheet of sun-print paper in total darkness, expose for seconds to minutes depending on the material, then develop or rinse. The same ultraviolet chemistry appears in sun prints, which are photography without a camera.
• Measure the resolution limit. Print a page of lines at decreasing spacing, stand the camera 2 m away, and record the finest line pair that stays separable through each of three hole sizes. Plot resolved spacing against hole diameter; the U-shaped curve with a minimum is the theory made visible.

What to Watch For Over the Next 3 Months

• Week 4: They notice pinhole images in the wild: the dappled patches under a tree in sunlight are actually overlapping images of the sun, which is why they go crescent-shaped during a partial eclipse.
• Month 2: They connect aperture to depth of field when using a phone camera’s portrait mode, or ask why a small aperture makes everything sharp.
• Month 3: If they ask why a lens is better than a hole, the answer, that a lens collects a wide cone from each point rather than a thin pencil and so is far brighter at the same sharpness, will land properly.

Frequently Asked Questions

Can I use a pinhole camera to look at a solar eclipse?

Not by looking through it. Use it as a projector: with your back to the sun, let the light pass through the hole onto a card held below, and look at the card. Direct viewing of the sun through any pinhole device risks permanent retinal damage, and no household filter makes it safe.

Why is the image upside down?

Because rays from the top of the scene travel downward through the hole and land low on the screen, while rays from the bottom travel upward and land high. The rays cross at the hole. The image is also reversed left to right for the same reason.

How big should the hole be?

About 0.6 mm for a 20 cm tube, from the optimum d ≈ 1.9√(λf). Scale it with the square root of the tube length: a 50 cm tube wants about 1 mm, and a 4 m room wants about 2.8 mm. Larger holes are brighter and blurrier.

Why can I see a lens-based image on my phone screen but this is so faint?

Because a hole of 0.6 mm has an area about 20,000 times smaller than a typical phone lens aperture, so it gathers that much less light from each point in the scene. A lens trades complexity for brightness. That is the entire reason lenses exist.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Young, M. (1971). “Pinhole Optics.” Applied Optics, 10(12), 2763. https://doi.org/10.1364/AO.10.002763
2. Stephenson, I. (2009). “Simulating diffraction limiting in a pinhole camera.” The Imaging Science Journal, 57(3), 162–166. https://doi.org/10.1179/174313109x442498
3. Matsutani, A. (2022). “Observation of libration and change in apparent diameter of the Moon with a pinhole camera.” Physics Education, 57, 055011. https://doi.org/10.1088/1361-6552/ac7b03
4. NASA Science. “Eclipse Viewing Safety.” https://science.nasa.gov/eclipses/safety/
5. American Academy of Ophthalmology. “Solar Eclipse Eye Safety.” https://www.aao.org/eye-health/tips-prevention/solar-eclipse-eye-safety
6. Exploratorium. “Pinhole Magnifier.” Science Snacks. https://www.exploratorium.edu/snacks/pinhole-magnifier
7. Galili, I., & Hazan, A. (2000). “Learners’ knowledge in optics: interpretation, structure and analysis.” International Journal of Science Education, 22(1), 57–88. https://doi.org/10.1080/095006900290000
8. National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. https://doi.org/10.17226/13165