Pinhole photography and camera obscura

Historical context

A camera obscura is a dark chamber with a small hole in one wall. Light passing through the hole projects an inverted, left-to-right reversed image of the scene on the opposite surface. Wikipedia's account of its history cites the Chinese Mozi (4th century BC) as one of the earliest written records, a passage in the Aristotelian Problems asking why sunlight through gaps forms round spots, Ibn al-Haytham's analysis of the phenomenon (965 to about 1040), and Johannes Kepler, who first used the term camera obscura in 1604. The Wikipedia pinhole camera page gives the first known description of pinhole photography as David Brewster's 1856 book The Stereoscope. We have not found a source naming one inventor of the pinhole camera, so no inventor or year is given.

A camera obscura can be a box, a tent or a whole room. Lenses were added from the late 16th century and the device became a drawing aid. Early 19th-century photographers, including Niépce, Daguerre and Fox Talbot, adapted box cameras to hold light-sensitive material.

What it is and how it differs

• No lens. A pinhole camera is a light-tight container with a tiny aperture. Eastman Museum notes that it tends to give long exposures and softer images than a lens camera.
• Great depth of field. The tiny aperture gives a very large depth of field, so objects at different distances are in equal focus.
• Curved film planes. If you use a round tin, straight lines appear curved because the image is projected onto a curved surface (Eastman Museum).
• Any light-sensitive material. Eastman's instructions use RC black and white photo paper, which makes a paper negative that is then contact printed. Film also works.

Camera-less relatives include the photogram. To calculate pinhole size and f-number for your own camera, use the pinhole calculator.

Materials and chemistry

Eastman Museum's materials list for a paper-negative camera:

Wikipedia gives the optimum pinhole diameter d for a pinhole-to-film distance f and wavelength λ as d = 2√(fλ) (Rayleigh, 1891), d = √(2fλ) (Petzval, 1857) or d ≈ 1.562√(fλ) (Young, 1971). At λ = 550 nm with both lengths in millimetres, Young's value simplifies to d ≈ 0.0366√f; for f = 50 mm that is about 0.259 mm, around f/193. The f-number is the pinhole-to-film distance divided by the pinhole diameter: 50 mm with a 0.5 mm hole gives f/100. The formulas disagree by tens of per cent, so treat them as starting points. A smaller hole is sharper but dimmer, until diffraction blurs the picture again.

Procedure

Steps follow Eastman Museum's guide, which says it is for use with adult supervision.

1. Seal gaps in the box with tape and paint the inside black.
2. Cut a small hole at one end of the box. With a tin, press a small hole into the metal and sand the inside smooth.
3. Make the pinhole by pricking a hole in foil with a pushpin, then tape the foil over the opening. The smaller the hole, the sharper the image. Wikipedia adds that the best pinholes are round and made in very thin material.
4. Make a shutter from a flap of foil or board.
5. Load paper in the darkroom under safelights, taped across from the pinhole. Close the shutter and camera before leaving the darkroom.
6. Expose by opening and closing the shutter, using the table below as a starting point.
7. Process the paper negative as the paper's instructions say.
8. Contact print the dry negative, image side against unexposed paper under glass or in a frame. Make a test strip first.

Practical tips

• Use a light-tight container and paint the inside black to cut stray reflections (Wikipedia).
• Pierce thin aluminium foil or brass with a sewing needle, then tape it behind a hole in the box.
• A cardboard flap works as a shutter.
• Depth of field is effectively unlimited, but blur still depends on the aperture size, wavelength, subject motion and haze.

Starting exposures (paper negative)

Add time if the negative is too light and take some away if it is too dark. Wikipedia notes that reciprocity failure sets in after about 1 second for film and about 30 seconds for paper, so long exposures need extra compensation.

Camera obscura and changing the view

A camera obscura can be scaled up from a box to a tent or a room with a small hole, with the view projected on an interior wall (Wikipedia). In a pinhole camera, the distance from pinhole to film sets the view. A shorter distance gives a wider view and a shorter exposure; a longer distance gives a narrower view and a longer exposure. A sliding film holder lets you change it. Wikipedia also lists artists who have worked with the camera obscura, including James Turrell, Abelardo Morell and Vera Lutter.

Troubleshooting

Safety

The camera itself is simple, but the printing stage uses darkroom chemicals, which we have not covered here because the paper's own instructions govern them. Read the SDS for your paper developer and fixer, and wear gloves and eye protection.

Further reading

Christopher James, The Book of Alternative Photographic Processes. Chapter 1 covers pinhole photography.

Sources

• Instructions for making a pinhole camera, George Eastman Museum
• Pinhole camera, Wikipedia
• Camera obscura, Wikipedia