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Pinhole cameraIn a world of ever-increasing sophistication, and cameras loaded with microchips and automated functions, it is an interesting and arguably refreshing experience to go back to basics. David Brewster, a Scottish physicist, carried out numerous important experiments in the field of optics, and in the 1850's became the first person to create a working pinhole camera.

Basic pinhole cameras are easy to make using only the simplest of materials. Take any medium-sized cardboard box, perhaps a shoe box, and cut a rectangular hole about 8 cm x 12 cm in one end. Tape greaseproof paper firmly over the hole. Cut another hole at the other end of the box, and tape aluminium foil over it. Then use a needle to pierce a small, neat hole in the centre of the foil. Direct the foil end of the box towards a well-lit object and observe the inverted image projected onto the greaseproof paper. Move the box to see the image change. This is a basic pinhole camera.

The image on the paper screen is produced because light travels in straight lines. In the diagram, light from the top of the tree passes through the pinhole and strikes the screen at the rear of the box. Light from the roots of the tree passes through the pinhole in the same way but strikes the screen in a different location. The image is therefore inverted and reversed. The projected image on the screen may be difficult to discern unless an effective shade is placed around it, because very little light passes through the tiny pinhole. Enlarging the pinhole increases the amount of light reaching the screen and makes the image easier to see, but also renders it less sharp. This is because the image-forming rays are less well focused.

Having created a basic pinhole camera, the next step is to produce a photograph. A piece of film or photographic paper should be fixed inside the box over the large aperture in place of the greaseproof paper. This must be done in a completely dark room. One side of a flap of lightproof material, such as aluminium foil, should then be taped in position to cover the pinhole. This acts as a simple shutter, allowing light into the box only when the flap is raised perhaps by pulling on a further length of tape or thread. This simple mechanism provides basic control over the exposure period.

More robust and practical pinhole cameras can be made in any form that retains the basic principles of operation described above. Indeed pinhole cameras have been made from beautifully-decorated custom-made timber boxes, old refrigerators and even railway carriages. The images they produce have almost infinite depth of field but are less sharp than those produced by a simple lens. They are also absolutely rectilinear even when wide-angle images are produced. However, pinhole images suffer from greater chromatic aberration and typically require very long exposures.

The designs of pinhole cameras may differ in a number of ways. Focal length, pinhole diameter, the number of pinholes, image format, flat and curved film planes, and the type of light-sensitive material must all be considered.

Strictly speaking, pinhole cameras have no focal length and infinite depth of field. However, the term "focal length" is commonly used to define the distance between the pinhole and the light-sensitive material. Pinhole cameras may be designed to have almost any focal length, and hence vary from extremely wide-angle to long telephoto cameras. However, as the focal length increases, so the aperture decreases and exposure period increase. The f-stop is given by the relationship F = L/D, where F is the aperture, L is the distance from the pinhole to the film plane, and D is the diameter of the pinhole. Beginners are well advised to start by making a wide-angle camera. For any given focal length there is an optimal pinhole diameter which produces maximum image sharpness. A number of formulas and charts are available to determine the ideal dimensions. A small pinhole generally produces a sharper image than a large one, but if the pinhole gets too small image may become less sharp because of diffraction.

Basic pinhole cameras have just one pinhole, but multiple pinhole cameras can be used to produce overlapping and hence panoramic images. Beginners should certainly start with a camera with a single pinhole. They may also have very different image formats. Some are made by replacing the lens of a 35mm camera with a modified lens cap. Others are based upon cheap medium or large format cameras. However, most are created from a simple box or container, with a pinhole plate in one end and a simple mechanism for holding the paper or film in the other. The best results are arguably achieved by using medium or large format film, or photographic paper of a comparable size. The use of 120-size roll film is a good compromise starting point.

The film plane of a pinhole camera may be flat or curved. Light fall-off may be apparent at the corners of an image when wide-angle pinhole cameras use a flat film plane, and it may prove impossible to avoid images being overexposed at the centre and underexposed at the corners. Vignetting may also occur, although this can be exploited as an aesthetic effect. A curved film plane avoids light fall-off because every part of the film is virtually the same distance from the pinhole. Large biscuit tins are sometimes employed for this purpose. They are cut in half and the film is fixed to the inside of the semi-circular container wall.

With flat film planes a pinhole has a usable circular image of approx. 125 degrees. The image diameter is about 3 1/2 times of any focal length. The image will fade towards the edges because of the increasing focal distance. With curved film planes a pinhole camera may have a larger circle of coverage (approximately 160 degrees).

Pinhole images may be created using either film or photographic paper. Black-and-white and colour negative films have more exposure latitude than transparency film. Ilford XP-2 black-and-white film has very wide exposure latitude and may consequently be exposed at anything between ISO 50 and 800. Photographic paper for black-and-white work, such as Ilford Multigrade III RC, has a low ISO rating. Matt paper is generally recommended for curved image planes where reflected light may be more of a problem. Glossy paper may be practical in cameras with flat image planes where light will not likely to be reflected. Reciprocity failure must be taken into account when calculating long exposures for both for film and paper.

Useful links to websites related to pinhole photography include:

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