Pinhole camera
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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.
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[edit] Invention of pinhole camera
Very early in history (as far back as 500 B.C.), Greeks such as Aristotle and Euclid wrote on naturally-occurring rudimentary pinhole cameras, for example through the slits of wicker baskets and the crossing of leaves, which can leave very small spaces through which light may travel. At the same time, the Chinese( Mo Ti and Chuang Chou, for example) were experimenting with and writing on the phenomenon. The aperture (pinhole) for instance, was referred to by Mo Ti in ca. 420 B.C. as the "collecting place". Robert Grosseteste and Roger Bacon during the 13th century commented on the pinhole camera. Men like Gemma-Frisius, Alhazen, and Porta between 1000 and 1600 wrote on the pinhole camera and began to explain in more details why the images were upside down. Pinhole images allowed the safe viewing of eclipses because the viewer was seeing the pinhole image and not the eclipse itself.
[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.
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:
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[1]. For 5cm it's .32mm [2].)
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
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] An example of a pinhole photographer
Wolf Howard is a member of the Stuckism Photography group and is a dedicated user of the pinhole camera. His approach provides an example of philosophy, equipment and working methods common to many in the genre.
He uses a light-proof wooden box 4" square with a fixed-size pinhole in the front. Photographic paper is placed at the back of the box. There is no lens and no viewfinder, so he estimates the aim of the camera. A wooden slider allows light into the box for an exposure which is between 40 seconds and 5 minutes. The camera is placed inside a light-proof bag to replace the photographic paper. He develops a negative print (in his bathroom) and makes the final positive print by placing another sheet of photographic paper under the negative with a 5 second exposure under a light bulb. The whole process requires estimation throughout and he "faces many disappointments in his darkroom. The hard work will eventually pay off."
He describes his fascination with the process:
| “ | There is something special about a pinhole camera. There is a beauty in its simplicity and rawness that technology has not been able to better. There is a timeless quality that can make the most uncomplicated subject seem full of poetry.
In each pinhole picture I take I hope to capture the joy and excitement that the early pioneering photographers (Fox Talbot and friends) must have felt when they took and developed photographs for the very first time.[1] |
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[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.
[edit] See also
[edit] Notes and references
- ^ "Stuckism: Wolf Howard" stuckism.com. Accessed April 21, 2006
