A dark room,
a bright hole.
Black out a room, make one hole, and the world outside paints itself upside down on the far wall. Set how deep the room is and how big that wall is; everything else — the size of the hole, how bright the picture will be, and how long your eyes need in the dark — falls out of those two numbers. Drag the screen wall in the drawing.
Fine print
550 nm is the green the eye is most sensitive to — the right choice for a room you look at. There is rarely a reason to move it.
| Conditions | Brightness | Eye | Phone |
|---|
Brightness is how much light the wall gives back; the eye column says how the picture will read once your eyes have adapted; the phone column says what it takes to photograph — an ordinary snap, Night mode, a propped phone, or a several-minute astro stack. Eyes, walls and phones all vary — treat every verdict as the middle of a range.
Making the hole — and the dark
The hole is the easy half: round, clean-edged, in something thin, mounted over a bigger port so you can swap sizes. The hard half is the darkness — a camera obscura is only as good as its blackout.
Cover every window with flattened cardboard or black polyethylene, taped at the edges — light leaks at corners matter more than the material. Kill standby LEDs and glowing switches; they look like nothing until your eyes adapt. Cut the hole's port in the blackout over the window with the best view, and make the aperture a separate thin plate taped over it, so changing hole sizes takes seconds. Then give your eyes time: the picture is at its best fifteen minutes after you think it has finished appearing.
Hole gauge
Measure the 50 mm bar with a real ruler first. If it comes out at 50 mm, every circle on this sheet is life-size — trace your aperture onto the plate, or check a drilled hole against its circle.
Or try a zone plate
Concentric rings sized so what gets through arrives in phase. Against a small sharp hole it passes several times the light — at the price of a soft, dreamy veil over the picture; against a big viewing hole it mostly offers the glow. At room depths the rings are big enough to laser-print directly.
How do I actually make this?
Room-scale plates print directly. At a few metres of depth the narrowest ring is a fifth of a millimetre or more — a 1200 dpi laser renders it cleanly on transparency film. One caveat: single-pass toner is not truly opaque and leaks light through the black. Print the card twice and sandwich the two copies in register, or use a pigment inkjet on film, which blocks far better.
Box-scale plates don't. Under about a metre of depth the rings shrink past what any office printer resolves. Print at 4× or 10× and photograph the card down onto litho film, or send the pattern to a PCB photoplotting service — they make film masks with 0.025 mm features cheaply, and their film is properly opaque.
Know what you're getting. The plate brightens the room severalfold, but most of the extra light arrives as a soft, unfocused veil over the picture — large shapes keep their contrast, fine detail goes gentle and glowing. Artists use zone plates in obscuras precisely for that look; if you want maximum crispness, stay with the hole.
| Zone | True radius | Drawn radius | Ring |
|---|
Zone plate — cut out and mount
Measure the 50 mm bar with a real ruler first. If it comes out at 50 mm, the plate below is drawn at exactly the scale stated — at 1×, print two copies on transparency, sandwich them in register, and mount over the port; at 4× or 10×, photograph it down onto litho film.
See it, then photograph it
The room is built and dark. Two acts remain: choosing what the wall looks at, and taking the picture home on a phone. The live verdict on step 01 names the mode your current wall needs.
Depth. The picture is honest perspective: things ten metres and further away land sharp and layered; a fence right outside the hole is just one blurry surface filling the wall.
Sun. The sun should light your scene, never shine into the hole — sun in the hole washes the whole wall grey. A window facing away from the sun's path gives soft, even pictures all day; a sunlit street works best with the sun behind or beside your wall.
Subject. Lit buildings, trees and passing traffic beat open sky — and remember the flip: the sky lands on your floor and the ground on your ceiling, so a view with interest low down puts it high on the wall.
Photograph the collision, not the wall. Step back until a bed or a chair sits in the bottom of the frame — the picture is the world falling on your furniture, not the wall alone.
Hunt the fold. Aim into a corner, or up where wall meets ceiling — the world bending around the room is the shot no ordinary photo can fake.
Move the hole, not the furniture. The picture follows the hole, and the horizon always crosses the wall at the hole's exact height.
Shoot from beside the hole, back to the window — everything you face is a lit screen, and the blinding hole stays out of frame.
Put someone in it. Stand them where the picture falls and have them hold statue-still — the world paints itself across anyone who can freeze.
Make a series. Tape a mark where the phone stands and reshoot at morning, noon and dusk — the room is a camera that never moves, so the frames line themselves up.
Give them fifteen minutes of honest darkness — the picture is at its best well after you think it has finished appearing. And keep the phone face-down until the end: one glance at a lit screen undoes twenty minutes of adaptation. If the room still looks empty, hunt leaks first — adapt, then walk the room and look for glow at the blackout edges.
Wipe the lens. A phone that has lived in a pocket wears an invisible film of grease, and grease scatters faint light into fog — exactly what this wall cannot spare. Ten seconds with a shirt hem.
Two switches first. Flash off — not Auto, off: in a room this dark Auto means it fires, and one flash torches the picture and everyone's night vision at once. Then Live Photo off. Either one quietly disables Night mode entirely, and you get an instant black frame instead of the long exposure the verdict promised.
Silence it, dim it. Airplane mode, screen brightness all the way down. One notification mid-exposure buzzes your propped phone and lights the room — in here the screen is the brightest lamp there is.
Prop it, use the main 1× lens. The wide and zoom lenses gather less light. Something solid, facing the wall — a propped, dead-still phone is what unlocks the longest exposures. Fire with the 3-second timer, or from a distance: a wired earbud's volume button is a shutter release, and a watch can run the camera remotely.
Keep it dark on purpose. Night modes are built to turn night into day, and they will happily wash your dim wall into grey noon. Press and hold on the picture until the phone says AE/AF LOCK — focus stops hunting too — then drag the little sun downward until the wall on screen looks like the wall in the room: dim, deep, believable.
Ask for the whole exposure. The phone chooses how long to bank light, and on Auto it often settles for a few seconds. iPhone: tap the arrow above the frame, tap the Night moon, drag the slider to Max — the full half-minute appears only once the phone is propped. Pixel: open Night Sight and set the phone down; when the shutter's moon turns to stars, the astro stack is armed.
Let the world move. Over half a minute, clouds pull into streaks and passing cars erase themselves — that smear is the picture's clock. The one thing that must not move is a person: anyone in frame holds statue-still, or becomes a ghost.
Afterwards. Don't mount the phone upside down to fix the flip — it notices gravity and rights the file anyway. Rotate the finished photo 180° in the edit screen: two taps. And if your phone offers a raw file (ProRAW, Expert RAW), keep it — the wall is painted in real daylight, and raw lets you say so when the phone guesses amber.
An ordinary snap only works on the brightest walls — big hole, full sun.
Night mode, handheld banks a few seconds of light; good for the clear-picture range.
Night mode, propped stretches to its longest exposure, about half a minute — most well-designed rooms in sun.
An astro stack (Pixel astrophotography, Expert RAW) banks minutes and reaches walls your eye calls faint. Beyond that, brighten the room instead.
The master of this exact act is Abelardo Morell, photographing room camera obscuras since 1991 — Manhattan spread upside down across a hotel bed, Venice pouring over a ceiling — and later projecting landscapes onto the ground itself with a tent camera. His digital-era exposures run two to four minutes: the astro rung above, exactly. The pictures are worth the visit.