LESSON 66
Pinhole
A camera with no lens at all.
IN THIS LESSON
- A box with a hole
- How big the hole should be
- Uses
- In practice: make one
A box with a hole
A pinhole camera has no lens, only a tiny opening: in effect a light-tight box with a small hole in one side. Light from the scene passes through the hole and projects an upside-down image on the opposite wall, the same effect as a camera obscura. The image grows as the wall moves further from the hole. The effect itself is ancient. Early descriptions appear in the Chinese Mozi writings of around 500 BCE, and Ibn al-Haytham described it in the eleventh century. The term pin-hole in optics appears in James Ferguson's book of 1764, and the first known description of pinhole photography is in David Brewster's book The Stereoscope of 1856.
How big the hole should be
A bigger hole lets in more light but blurs the image; a smaller one sharpens it until diffraction takes over and blurs it again. So there is a best size for each distance between hole and film. Joseph Petzval first published a way to calculate it in 1857: the diameter equals 1.41 times the square root of that distance times the wavelength of light. Lord Rayleigh applied wave theory in 1891 and arrived at a hole about 41 percent bigger. The table uses Petzval's formula with green light at 550 nanometres, our choice, and shows the resulting f-number and how many stops darker that is than f/16. The figures are computed here.
Uses
Pinhole images are soft, have nearly unlimited depth of field and need long exposures, which gives them a quiet, dreamy look. The source names several uses: art, teaching the basics of photography, and solarigraphy, in which a pinhole camera left in place for weeks or months records the path of the sun across the sky. Pinhole projection is also a safe way to watch a solar eclipse. A Worldwide Pinhole Photography Day is held on the last Sunday of April each year. Manufactured pinholes can be fitted to digital cameras in place of a lens, which makes trial and error cheap.
In practice: make one
This section is working practice, built on the source's description. Use a light-tight tin or box, painted matte black inside. Pierce a piece of thin aluminium from a drinks can with a fine needle, sand the burr, and check the hole under a loupe; tape it behind a larger hole in the box. A flap of card and tape makes the shutter. Load photographic paper in the dark as the negative, expose for anything from seconds in bright sun to minutes in shade, develop the paper, and contact print it to get a positive. Or tape a pinhole over a body cap on a digital camera and check exposure on the screen.
| Pinhole to film | Best diameter | f-number | Stops darker than f/16 |
|---|---|---|---|
| 25 mm | 0.17 mm | f/151 | 6.5 |
| 50 mm | 0.23 mm | f/214 | 7.5 |
| 100 mm | 0.33 mm | f/302 | 8.5 |
| 150 mm | 0.40 mm | f/370 | 9.1 |
Try it today
- 01Drill a small hole in a spare body cap and tape a pinhole in thin metal over it.
- 02Fit it to your camera, set ISO 400 and a tripod.
- 03Use the table to estimate the f-number and the exposure from a normal meter reading.
- 04Shoot a bright scene with a close object in front and note the deep focus.
- 05Try a long exposure of people walking past and see them vanish.