Pinhole camera

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== Image:PinholeCameraAndRelatedSupplies.jpg

A pinhole camera is a camera without a conventional glass lens. An extremely small hole in a very thin material can focus light by confining all rays from a scene through a single point. In order to produce a reasonably clear image, the aperture has to be a small pinhole on the order of 0.5 mm (0.02 inches) or less. The shutter of a pinhole camera usually consists of a hand operated flap of some light-proof material to cover and uncover the pinhole. Pinhole cameras require much longer exposure times than conventional cameras because of the small aperture; typical exposure times can range from 5 seconds to hours or days.

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.

In the arts, digital cameras encourage artistic experimentation due to the elimination of film and processing costs; as a result, some photographers have tried making their own pinhole lenses for digital camera bodies, usually using a body cap with an extremely tiny hole in the center. The results show significant optical aberrations, but can nonetheless be artistically pleasing. In addition, extensive post processing in image enhancement software such as photoshop can minimize much of the distortion, thus resulting in a surprisingly good image. However, in terms of quality and convenience, a pinhole lens is no match for a conventional optical lens.

1 Invention of Pinhole camera
2 Selection of pinhole size
3 Pinhole camera construction
4 Calculating the f-stop & required exposure
5 Worldwide Pinhole Photography Day
6 See also
7 Notes and references
8 External links

[edit] Invention of Pinhole camera

Ibn Al-Haytham (Alhazen), an Islamic mathematician, astronomer, and physicist invented the pinhole camera around 1000 Gregorian Calendar and explained why the image was upside down. Later around 1600, Della Porta reinvented the pinhole camera. Apparently he was the first European to publish any information on the pinhole camera and is sometimes incorrectly credited with its invention. [1]

[edit] 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. 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 have access to laser etching, but a hobbyist can still produce pinholes of sufficiently high quality for photographic work.

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, use fine sand paper to reduce the thickness of the material in the center to the bare 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 was improved upon by Lord Rayleigh into the form used today:

<math>d=1.9\sqrt{f \lambda}</math>

Where d is diameter, f is focus length (distance from hole to photographic film) 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 1 inch, this works out to a pinhole .22mm in diameter[2]. For 5cm it's .32mm [3].)

The depth of field is basically infinite, but this does not mean everything will definitely be in focus. Depending on the distance from the aperture to the film plane, the infinite depth of field means everything is either in or out of focus to the same degree.

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

[edit] Pinhole camera construction

Image:PinholeCameraCloseup.jpg 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 35mm 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.

[edit] Calculating the f-stop & required exposure

The f-stop of the camera may be calculated by dividing the diameter of the pinhole into the focal length of the camera. The diameter of the pinhole can be determined by knowing the diameter of the needle or drill used to make the hole. The focal length is the distance from the film to 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-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 for film has exceeded 1 second, or that of paper has exceeded 30s - one must compensate for the breakdown in linear response of the film 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 NAIC) has funded initial research into the New Worlds Imager 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.

[edit] Worldwide Pinhole Photography Day

On the last Sunday in April, also known as "World Pinhole Day", people all over the world take a single picture with a home made pinhole camera and submit it to the Worldwide Pinhole Photography Day website.