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

A pinhole camera is a very simple camera with no lens and a single very small aperture. Simply explained, it is a light-proof box with a small hole in one side. Light from a scene passes through this single point and projects an inverted image on the opposite side of the box. Cameras using small apertures and the human eye in bright light both act like a pinhole camera.

The smaller the hole, the sharper the image, but the dimmer the projected image. Optimally, the size of the aperture should be 1/100 or less of the distance between it and the screen.

A pinhole camera's shutter is usually manually operated because of the lengthy exposure times, and consists of a flap of some light-proof material to cover and uncover the pinhole. Typical exposures range from 5 seconds to hours and sometimes days.

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

The image may be projected onto a translucent screen for real-time viewing (popular for observing solar eclipses; see also camera obscura), or can expose film or a charge coupled device (CCD). Pinhole cameras with CCDs are often used for surveillance because they are difficult to detect.

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.

It was the 10th-century Arab physicist, astronomer and mathematician, Ibn al-Haytham (Alhazen), who published this idea in the Book of Optics in 1021 AD. When Ibn al-Haytham began experimenting with the camera obscura , he himself stated, Et nos non inventimus ita, "we did not invent this". He improved on the camera after realizing that the smaller the pinhole, the sharper the image (though the less light). He provides the first clear description for construction of a 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.

In the 5th century BC, the Mohist philosopher Mo Jing (墨經) in ancient China mentioned the effect of an inverted image forming through a pinhole. The image of an inverted Chinese pagoda is mentioned in Duan Chengshi's (d. 863) book Miscellaneous Morsels from Youyang written during the Tang Dynasty (618–907). 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 for the eyes when viewing solar eclipses because the event is observed indirectly, the diminished intensity of the pinhole image being harmless compared with the full glare of the Sun itself.

Around 1600, Giambattista della Porta add a lens to the pinhole camera. It was not until 1850 that a Scottish scientist by the name of Sir David Brewster actually took the first actual photograph with a pinhole camera. Up until recently It was believed that Brewster himself coined the term "Pinhole" in "The Stereoscope". The earliest reference to the term "Pinhole has been traced back to almost a century before Brewster to James Ferguson's Lectures on select Subjects. Sir William Crookes and William de Wiveleslie Abney were other early photographers to try the pinhole technique.

Selection of pinhole size

Generally, a smaller pinhole (with a thinner surface that the hole goes through) will result in sharper image resolution as the projected circle of confusion is smaller at the image plane. The thinner and smaller, the more resolution. This is why a lot of pinhole instructions tell you to sand the surface the hole is in. An extremely small hole, however, can produce significant diffraction effects and 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 occurs, as less light reaches the edges of the image. This is due to the sides of the hole shading the light coming in at anything other than 90 degrees.

The best pinhole is perfectly round (since irregularities cause higher-order diffraction effects), 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.

An example of a 20 minute exposure taken with a pinhole camera

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

Some examples of photographs taken using a pinhole camera.
One often quoted method is to start with a sheet of brass shim or metal reclaimed from an aluminium drinks can or tin foil/aluminum foil, use fine sand paper to reduce the thickness of the centre of the material to the minimum, before carefully creating a pinhole with a suitably sized needle – sanding away the burrs on either side & rotating the pin as it glides in and out in order to produce a smooth circular hole.

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

d=1.9\sqrt{f\lambda}where d is diameter, f is focal length (distance from pinhole to focal plane) and λ is the wavelength of light.

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 0.22 mm in diameter. For 5 cm, the appropriate diameter is 0.32 mm.

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 depends not on object distance, but on other factors, such as the distance from the aperture to the film plane, the aperture size, and the wavelength(s) of the light source.

Pinhole camera construction

Pinhole cameras are usually handmade by the photographer for a particular purpose. In its simplest form, the photographic pinhole camera consists of a light-tight box with a pinhole in one end, and a piece of film or photographic paper wedged or taped into the other end.A flap of cardboard with a tape hinge can be used as a shutter.The pinhole is usually punched or drilled using a sewing needle or small diameter bit through a piece of tinfoil or thin aluminum or brass sheet.This piece is then taped to the inside of the light tight box behind a hole cut through the box. An oatmeal box can be made into an excellent pinhole camera.

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 and focusing assembly has been damaged can be reused as pinhole cameras—maintaining the use of the shutter and film winding mechanisms. As a result of the enormous increase in f-number while maintaining the same exposure time, one must use a fast film in direct sunshine.

Pinholes (homemade or commercial) can be used in place of the lens on an SLR. Use with a digital SLR allows metering and composition by trial and error, and is effectively free, so is a popular way to try pinhole photography.

Calculating the f-number & required exposure

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.

The f-number of the camera may be calculated by dividing the distance from the pinhole to the imaging plane (the focal length) by the diameter of the pinhole. 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-number of 2/0.02 (50/0.5), or 100 (f/100 in conventional notation).

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.

NASAmarker (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 Toromarker fighter base in Irvine, Californiamarker, a team of six photographer artists and an army of assistants created the world's largest pinhole camera, using 1½ miles of wide black Gorilla Tape and of black spray paint to make the hangar light-tight. The aim was to make a black-and-white negative print of the Marine Corps air station with its control tower and runways, with the San Joaquin Hillsmarker in the background. 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, as well as 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 litres of gelatin silver halide. and it was hung from the ceiling at a distance of about from a pinhole, just under in diameter, situated above ground level in the wall. The distance between the pinhole and the cloth was determined 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 of traditional developer and 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.

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