Principle of a pinhole camera. Light rays from an object pass through a small hole to form an image.

Holes in the leaf canopy project images of a solar eclipse on the ground.

A home-made pinhole camera (on the left), wrapped in black plastic to prevent light leaks, and related developing supplies.

A pinhole camera is a camera without a lens. An extremely small hole takes its place, which should be in very thin material. An image's light from a scene passes through this single point, the image on the light-sensitive material will be upside-down, and clear at all distances from the pinhole. The smaller the hole, the sharper the image, but the more exposure will be required. Also, in order to produce a reasonably clear image, the ratio of the pinhole, or aperture, size to the distance between it and the screen should be 1/100 or less. The shutter of a pinhole camera is usually manually operated because of the lengthy times, and consists of a flap of some light-proof material to cover and uncover the pinhole. Typical exposure times range from 5 seconds to hours and sometimes days.

A common use of a pinhole camera is to capture the movement of sunlight over a long period of time. This type of photography is called Solargraphy.

The image may be projected on a translucent screen for real-time viewing (popular for viewing solar eclipses; see also camera obscura), or can expose film or a charge coupled device (CCD). Pinhole cameras with CCDs are sometimes used for surveillance work because of their small size.

Invention of pinhole camera

As far back as the 4th century BC, Greeks such as Aristotle and Euclid wrote on naturally-occurring rudimentary pinhole cameras. For example, light may travel through the slits of wicker baskets or the crossing of tree leaves ^[1] The ancient Greeks, however, believed that vision is enabled by rays emitted from the eye. The discovery that vision results from rays entering the eye rather than being emitted by it enabled a much better understanding of the pinhole camera effect. It was the 10th-century Muslim physicist, astronomer and mathematician, Ibn al-Haytham (Alhazen), who published this idea in the Book of Optics in 1021 AD. He also invented the first pinhole camera after noticing the way light was streaming through a hole in a window shutter. He improved on the camera after realizing that the smaller the pinhole, the sharper the image (though the less light). He designed the first camera obscura (Lat. dark chamber). As a side benefit of his invention, he was credited with being first man to shift physics from a philosophical to an experimental basis.^[2]

In the 5th century BC, the Mohist philosopher Mo Jing (??) in ancient China mentioned the effect of an "image forming through a pinhole". Along with experimenting with the pinhole camera and the burning mirror of the ancient Mohists, the Song Dynasty (960-1279 AD) Chinese scientist Shen Kuo (1031-1095) experimented with camera obscura and was the first to establish geometrical and quantitative attributes for it. In the 13th century , Robert Grosseteste and Roger Bacon commented on the pinhole camera. Between 1000 and 1600, men such as Ibn al-Haytham, Gemma Frisius, and Giambattista della Porta wrote on the pinhole camera, explaining why the images are upside down. Pinhole devices provide safety in viewing solar eclipses because the observer views the diminished intensity of the pinhole image rather than the full light of the eclipse itself.

Selection of pinhole size

Generally, a smaller pinhole will result in better image resolution (sharper picture) as the projected circle of confusion is smaller at the image plane. An extremely small hole, however, can produce significant diffraction effects which will result in a less clear image due to the wave properties of light. Additionally, as the diameter of the hole approaches the thickness of the material in which it is punched, significant vignetting at the edges of the image will result, as less light will reach these areas. This is due to the shading effect of the sides of the hole for light coming in at other than a 90 degree angle.

The best pinhole is perfectly round (to minimise any higher-order diffraction effects off irregularites), and in an extremely thin piece of material. Industrially produced pinholes benefit from laser etching, but a hobbyist can still produce pinholes of sufficiently high quality for photographic work.

A photograph taken with a pinhole camera using an exposure time of 2 seconds

Some examples of photographs taken using a pinhole camera.

A method of calculating the optimal pinhole diameter was first attempted by Jozef Petzval. The formula was improved upon by Lord Rayleigh into the form used today:

d=1.9\sqrt{f \lambda}

Where d is diameter, f is focus length (distance from hole to photographic film) and ? is the wavelength of light, all given in metres.

For standard black and white film, a wavelength of light corresponding to yellow-green (550 nm) should yield optimum results. (For a pinhole to film distance of , this works out to a pinhole .22mm in diameterhttp://www.google.com/search?q=1.9+sqrt(1inch*550nm)=. For 5 cm it's .32mm http://www.google.com/search?q=1.9+sqrt(5cm*550nm)=.)

The depth of field is basically infinite, but this does not mean that no optical blurring occurs. The infinite depth of field means that image blur does not depend on scene distance, but it does depend on other factors, such as the distance from the aperture to the film plane, the aperture size, and the wavelength(s) of the illumination.

Just as in a conventional glass lens, the image is inverted, as shown in the diagram above.

Pinhole camera construction

A pinhole camera made from an oatmeal box. The pinhole is in the centre. The black plastic which normally surrounds this camera (see picture above) has been removed.

Pinhole cameras are often constructed with a sliding film holder or back so that the distance between the film and the pinhole can be adjusted. This allows the angle of view of the camera to be changed and also the effective f-stop ratio of the camera. Moving the film closer to the pinhole will result in a wide angle field of view and a shorter exposure time. Moving the film farther away from the pinhole will result in a telephoto or narrow angle view and a longer exposure time.

Pinhole cameras can also be constructed by replacing the lens assembly in a conventional camera with a pinhole. In particular, compact 35 mm cameras whose lens & focusing assembly has been damaged (smashed lens, dropped in sand etc.) can be reused as pinholes - maintaining the use of the shutter & film wind on mechanics. As a result of the enormous increase in f-stop while maintaining the same exposure time, one must use a fast film in direct sunshine.

Calculating the f-stop & required exposure

A fire hydrant photographed by a pinhole camera made from a shoe box, exposed on photographic paper (top). The length of the exposure was 40 seconds. There is noticeable flaring in the bottom-right corner of the image, likely due to extraneous light entering the camera box.

The f-stop of the camera may be calculated by dividing the diameter of the pinhole by the distance from the pinhole to the imaging plane (the focal length). For example, a camera with a 0.02 inch (0.5 mm) diameter pinhole, and a 2 inch (50 mm) focal length would have an f-stop of 2/0.02 (50/0.5), or 100.

Due to the large f-number of a pinhole camera, exposures will often encounter reciprocity failure. Once exposure time has exceeded about 1 second for film or 30 seconds for paper, one must compensate for the breakdown in linear response of the film/paper to intensity of illumination by using longer exposures.

Other special features can be built into pinhole cameras such as the ability to take double images, by using multiple pinholes, or the ability to take pictures in cylindrical or spherical perspective by curving the film plane.

These characteristics could be used for creative purposes. Once considered as an obsolete technique from the early days of photography, pinhole photography is from time to time a trend in artistic photography.

Related cameras, image forming devices, or developments from it include Franke's widefield pinhole camera, the pinspeck camera, and the pinhead mirror.

NASA (via the NASA Institute for Advanced Concepts) has funded initial research into the New Worlds Mission project, which proposes to use a pinhole camera with a diameter of 10 m and focus length of 200,000 km to image earth sized planets in other star systems.

World's largest pinhole camera

In an abandoned F-18 hangar at the closed El Toro fighter base in Irvine, California, a team of six photographer artists and an army of assistants created the world's largest pinhole camera, using 1½ miles of 2" wide black gorilla tape and 40 gallons of black spray paint to make it light-tight. The subject was the Marine Corps air station with its control tower and runways, against a background of the San Joaquin Hills, to make a black and white finished print in negative appearance. The purpose was to subscribe to the Legacy Project, a photographic compilation and record of the airfield's history before it is transformed into a giant urban park. And also to demonstrate to the digital world the value of print making the 168-year-old way.

A huge piece of muslin cloth was made light sensitive by coating it with 80 liters of gelatin silver halide. and it was hung from the ceiling at a distance of about from the wall where a just under ¼ inch pinhole was made above ground level. The distance between the pinhole and the cloth was decided to be for best coverage, and the exposure time was calculated at 35 minutes. The opaque negative image print was developed in an Olympic-swimming-pool-size tray with 600 gallons of traditional developer and 1200 gallons of fixer, and was washed using fire hoses attached to two fire hydrants. The resulting finished print was nearly . wide and . high and was exhibited for the first time at the Art Center College of Design in Pasadena, California, on September 6, 2007. ^{[3] [4]}.

See also

• Camera obscura
• Pinhole glasses
• New Worlds Mission
• Spatial filter
• Zone plate
• Dirkon
• Fox Talbot
• Wolf Howard
• Billy Childish
• Jesse Richards
• Pinhole camera model
• Nautilus (its lens-less eye functions as a pinhole camera)

Notes and references

1. ↑ "Light Through the Ages".
2. ↑ "How Islamic inventors changed the world", The Independent. Accessed April 6, 2007
3. ↑
4. ↑ The Legacy Project press release, dated June 8, 2007

External links

• Worldwide Pinhole Photography Day website
• Pinhole Photography and Camera Design Calculators
• Illustrated history of cinematography
• Plans to build the world's biggest camera

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